1
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Wang LX, Beugeling W, Schmitt F, Lunczer L, Mayer JB, Buhmann H, Hankiewicz EM, Molenkamp LW. Spectral Asymmetry Induces a Re-Entrant Quantum Hall Effect in a Topological Insulator. Adv Sci (Weinh) 2024; 11:e2307447. [PMID: 38477036 DOI: 10.1002/advs.202307447] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2023] [Revised: 01/29/2024] [Indexed: 03/14/2024]
Abstract
The band inversion of topological materials in three spatial dimensions is intimately connected to the parity anomaly of 2D massless Dirac fermions, known from quantum field theory. At finite magnetic fields, the parity anomaly reveals itself as a non-zero spectral asymmetry, i.e., an imbalance between the number of conduction and valence band Landau levels, due to the unpaired zero Landau level. This work reports the realization of this 2D Dirac physics at a single surface of the 3D topological insulator (Hg,Mn)Te. An unconventional re-entrant sequence of quantized Hall plateaus in the measured Hall resistance can be directly related to the occurrence of spectral asymmetry in a single topological surface state. The effect should be observable in any topological insulator where the transport is dominated by a single Dirac surface state.
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Affiliation(s)
- Li-Xian Wang
- Institute for Topological Insulators, Am Hubland, 97074, Würzburg, Germany
- Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Wouter Beugeling
- Institute for Topological Insulators, Am Hubland, 97074, Würzburg, Germany
- Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Fabian Schmitt
- Institute for Topological Insulators, Am Hubland, 97074, Würzburg, Germany
- Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Lukas Lunczer
- Institute for Topological Insulators, Am Hubland, 97074, Würzburg, Germany
- Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Julian-Benedikt Mayer
- Institute for Theoretical Physics and Astrophysics (TP IV), Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Hartmut Buhmann
- Institute for Topological Insulators, Am Hubland, 97074, Würzburg, Germany
- Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Ewelina M Hankiewicz
- Institute for Theoretical Physics and Astrophysics (TP IV), Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Laurens W Molenkamp
- Institute for Topological Insulators, Am Hubland, 97074, Würzburg, Germany
- Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
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2
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Thenapparambil A, Dos Santos GE, Li CA, Abdelghany M, Beugeling W, Buhmann H, Gould C, Zhang SB, Trauzettel B, Molenkamp LW. Fluctuations in Planar Magnetotransport Due to Tilted Dirac Cones in Topological Materials. Nano Lett 2023; 23:6914-6919. [PMID: 37498076 DOI: 10.1021/acs.nanolett.3c01508] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/28/2023]
Abstract
Fluctuations in planar magnetotransport are ubiquitous in topological HgTe structures, in both tensile (topological insulator) and compressively strained layers (Weyl semimetal phase). We show that the common reason for the fluctuations is the presence of tilted Dirac cones combined with the formation of charge puddles. The origin of the tilted Dirac cones is the mix of the Zeeman term due to the in-plane magnetic field and quadratic contributions to the dispersion relation. We develop a network model that mimics the transport of tilted Dirac fermions in the landscape of charge puddles. The model captures the essential features of the experimental data. It should be relevant for the interpretation of planar magnetotransport in a variety of topological and small band gap materials.
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Affiliation(s)
- Arya Thenapparambil
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, D-01187 Dresden, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Graciely Elias Dos Santos
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Chang-An Li
- Faculty for Physics and Astronomy (TP4), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Mohamed Abdelghany
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Wouter Beugeling
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Hartmut Buhmann
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Charles Gould
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Song-Bo Zhang
- Department of Physics, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
| | - Björn Trauzettel
- Faculty for Physics and Astronomy (TP4), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Laurens W Molenkamp
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, D-01187 Dresden, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
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3
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Fijalkowski KM, Liu N, Mandal P, Schreyeck S, Brunner K, Gould C, Molenkamp LW. Macroscopic Quantum Tunneling of a Topological Ferromagnet. Adv Sci (Weinh) 2023:e2303165. [PMID: 37314152 PMCID: PMC10401085 DOI: 10.1002/advs.202303165] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Indexed: 06/15/2023]
Abstract
The recent advent of topological states of matter spawned many significant discoveries. The quantum anomalous Hall (QAH) effect is a prime example due to its potential for applications in quantum metrology, as well as its influence on fundamental research into the underlying topological and magnetic states and into axion electrodynamics. Here, electronic transport studies on a (V,Bi,Sb)2 Te3 ferromagnetic topological insulator nanostructure in the QAH regime are presented. This allows access to the dynamics of an individual ferromagnetic domain. The domain size is estimated to be in the 50-100 nm range. Telegraph noise resulting from the magnetization fluctuations of this domain is observed in the Hall signal. Careful analysis of the influence of temperature and external magnetic field on the domain switching statistics provides evidence for quantum tunneling (QT) of magnetization in a macrospin state. This ferromagnetic macrospin is not only the largest magnetic object in which QT is observed, but also the first observation of the effect in a topological state of matter.
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Affiliation(s)
- Kajetan M Fijalkowski
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074, Würzburg, Germany
| | - Nan Liu
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074, Würzburg, Germany
| | - Pankaj Mandal
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074, Würzburg, Germany
| | - Steffen Schreyeck
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074, Würzburg, Germany
| | - Karl Brunner
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074, Würzburg, Germany
| | - Charles Gould
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074, Würzburg, Germany
| | - Laurens W Molenkamp
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074, Würzburg, Germany
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4
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Shekhar P, Bendias K, Fürst L, Liang X, Gbordzoe MK, Borzenko T, Buhmann H, Kleinlein J, Molenkamp LW. Realization of smooth side profile using diffusion-controlled wet chemical etching for HgTe/(Hg,Cd)Te heterostructures. Nanotechnology 2023; 34:205302. [PMID: 36753756 DOI: 10.1088/1361-6528/acba1d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Accepted: 02/08/2023] [Indexed: 06/18/2023]
Abstract
We utilize a diffusion-controlled wet chemical etching technique to fabricate microstructures from two-dimensional HgTe/(Hg,Cd)Te-based topological insulators. For this purpose, we employ a KI: I2: HBr: H2O-based etchant. Investigation of the side profile of the etched heterostructure reveals that HgTe quantum wells protrude from the layer stack as a result of the different etch rates of the layers. This constraint poses challenges for the study of the transport properties of edge channels in HgTe quantum wells. In order to achieve a smoother side profile, we develop a novel approach to the etching process involving the incorporation of a sacrificial design element in the etch mask. This limits the flow of charge carriers to the ions in the electrolyte during the etching process. The simplicity of the method coupled with the promising results achieved thereby should make it possible for the new approach introduced here to be applied to other semiconductor heterostructures.
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Affiliation(s)
- Pragya Shekhar
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Kalle Bendias
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Lena Fürst
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Xianhu Liang
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Michael K Gbordzoe
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Tatiana Borzenko
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Hartmut Buhmann
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Johannes Kleinlein
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Laurens W Molenkamp
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
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5
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Tielrooij KJ, Principi A, Reig DS, Block A, Varghese S, Schreyeck S, Brunner K, Karczewski G, Ilyakov I, Ponomaryov O, de Oliveira TVAG, Chen M, Deinert JC, Carbonell CG, Valenzuela SO, Molenkamp LW, Kiessling T, Astakhov GV, Kovalev S. Milliwatt terahertz harmonic generation from topological insulator metamaterials. Light Sci Appl 2022; 11:315. [PMID: 36316317 PMCID: PMC9622918 DOI: 10.1038/s41377-022-01008-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Revised: 09/07/2022] [Accepted: 10/08/2022] [Indexed: 05/15/2023]
Abstract
Achieving efficient, high-power harmonic generation in the terahertz spectral domain has technological applications, for example, in sixth generation (6G) communication networks. Massless Dirac fermions possess extremely large terahertz nonlinear susceptibilities and harmonic conversion efficiencies. However, the observed maximum generated harmonic power is limited, because of saturation effects at increasing incident powers, as shown recently for graphene. Here, we demonstrate room-temperature terahertz harmonic generation in a Bi2Se3 topological insulator and topological-insulator-grating metamaterial structures with surface-selective terahertz field enhancement. We obtain a third-harmonic power approaching the milliwatt range for an incident power of 75 mW-an improvement by two orders of magnitude compared to a benchmarked graphene sample. We establish a framework in which this exceptional performance is the result of thermodynamic harmonic generation by the massless topological surface states, benefiting from ultrafast dissipation of electronic heat via surface-bulk Coulomb interactions. These results are an important step towards on-chip terahertz (opto)electronic applications.
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Affiliation(s)
- Klaas-Jan Tielrooij
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), BIST and CSIC, Campus UAB, Bellaterra, Barcelona, 08193, Spain.
- Department of Applied Physics, TU Eindhoven, Den Dolech 2, 5612 AZ, Eindhoven, The Netherlands.
| | - Alessandro Principi
- School of Physics and Astronomy, University of Manchester, M13 9PL, Manchester, UK
| | - David Saleta Reig
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), BIST and CSIC, Campus UAB, Bellaterra, Barcelona, 08193, Spain
| | - Alexander Block
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), BIST and CSIC, Campus UAB, Bellaterra, Barcelona, 08193, Spain
| | - Sebin Varghese
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), BIST and CSIC, Campus UAB, Bellaterra, Barcelona, 08193, Spain
| | - Steffen Schreyeck
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Karl Brunner
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Grzegorz Karczewski
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
- Institute of Physics, Polish Academy of Science, Al. Lotnikow 32/46, PL-02668, Warsaw, Poland
| | - Igor Ilyakov
- Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany
| | - Oleksiy Ponomaryov
- Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany
| | | | - Min Chen
- Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany
| | - Jan-Christoph Deinert
- Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany
| | - Carmen Gomez Carbonell
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), BIST and CSIC, Campus UAB, Bellaterra, Barcelona, 08193, Spain
| | - Sergio O Valenzuela
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), BIST and CSIC, Campus UAB, Bellaterra, Barcelona, 08193, Spain
- ICREA, Pg. Lluís Companys 23, 08010, Barcelona, Spain
| | - Laurens W Molenkamp
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074, Würzburg, Germany
| | - Tobias Kiessling
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Georgy V Astakhov
- Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany.
| | - Sergey Kovalev
- Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany.
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6
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Shekhar P, Shamim S, Hartinger S, Schlereth R, Hock V, Buhmann H, Kleinlein J, Molenkamp LW. Low-Temperature Atomic Layer Deposition of Hafnium Oxide for Gating Applications. ACS Appl Mater Interfaces 2022; 14:33960-33967. [PMID: 35820660 DOI: 10.1021/acsami.2c06176] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
We present a novel low-temperature (30 °C) atomic layer deposition process for hafnium oxide and apply the layers as gate dielectric to fabricate devices out of the thermally sensitive topological insulator HgTe. The key to achieving self-limiting growth at these low temperatures is the incorporation of sufficiently long purge times ( ≥150 s) in the deposition cycles. We investigate the structural and compositional properties of these thin films using X-ray reflectometry and photoelectron spectroscopy, finding a growth rate of 1.6 Å per cycle and an atomic ratio of Hf/O of 1:1.85. In addition, we report on the transport properties of the microstructured devices, which are much enhanced compared to previous device generations. We determine a relative permittivity of ∼15 for our HfO2 layers. Our process considerably reduces the thermal load of the samples during microfabrication and can be adapted to a broad range of materials, enabling the fabrication of high-quality gate insulators on various temperature-sensitive materials.
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Affiliation(s)
- Pragya Shekhar
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, 97074 Würzburg, Germany
| | - Saquib Shamim
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, 97074 Würzburg, Germany
| | - Simon Hartinger
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, 97074 Würzburg, Germany
| | - Raimund Schlereth
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, 97074 Würzburg, Germany
| | - Volkmar Hock
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, 97074 Würzburg, Germany
| | - Hartmut Buhmann
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, 97074 Würzburg, Germany
| | - Johannes Kleinlein
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, 97074 Würzburg, Germany
| | - Laurens W Molenkamp
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, 97074 Würzburg, Germany
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7
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Shamim S, Shekhar P, Beugeling W, Böttcher J, Budewitz A, Mayer JB, Lunczer L, Hankiewicz EM, Buhmann H, Molenkamp LW. Counterpropagating topological and quantum Hall edge channels. Nat Commun 2022; 13:2682. [PMID: 35562333 PMCID: PMC9106760 DOI: 10.1038/s41467-022-29815-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Accepted: 03/30/2022] [Indexed: 11/09/2022] Open
Abstract
The survival of the quantum spin Hall edge channels in presence of an external magnetic field has been a subject of experimental and theoretical research. The inversion of Landau levels that accommodates the quantum spin Hall effect is destroyed at a critical magnetic field, and a trivial insulating gap appears in the spectrum for stronger fields. In this work, we report the absence of this transport gap in disordered two dimensional topological insulators in perpendicular magnetic fields of up to 16 T. Instead, we observe that a topological edge channel (from band inversion) coexists with a counterpropagating quantum Hall edge channel for magnetic fields at which the transition to the insulating regime is expected. For larger fields, we observe only the quantum Hall edge channel with transverse resistance close to h/e2. By tuning the disorder using different fabrication processes, we find evidence that this unexpected ν = 1 plateau originates from extended quantum Hall edge channels along a continuous network of charge puddles at the edges of the device.
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Affiliation(s)
- Saquib Shamim
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany. .,Institute for Topological Insulators, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
| | - Pragya Shekhar
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.,Institute for Topological Insulators, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Wouter Beugeling
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.,Institute for Topological Insulators, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Jan Böttcher
- Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Andreas Budewitz
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.,Institute for Topological Insulators, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Julian-Benedikt Mayer
- Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Lukas Lunczer
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.,Institute for Topological Insulators, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Ewelina M Hankiewicz
- Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Hartmut Buhmann
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.,Institute for Topological Insulators, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Laurens W Molenkamp
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany. .,Institute for Topological Insulators, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
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8
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Mandal P, Taufertshöfer N, Lunczer L, Stehno MP, Gould C, Molenkamp LW. Finite Field Transport Response of a Dilute Magnetic Topological Insulator-Based Josephson Junction. Nano Lett 2022; 22:3557-3561. [PMID: 35471102 DOI: 10.1021/acs.nanolett.1c04903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Hybrid samples combining superconductors with magnetic topological insulators are a promising platform for exploring exotic new transport physics. We examine a Josephson junction of such a system based on the dilute magnetic topological insulator (Hg,Mn)Te and the type II superconductor MoRe. In the zero and very low field limits, to the best of our knowledge, the device shows, for the first time, an induced supercurrent through a magnetically doped semiconductor, in this case, a topological insulator. At higher fields, a rich and hysteretic magnetoresistance is revealed. Careful analysis shows that the explanation of this behavior can be found in magnetic flux focusing stemming from the Meissner effect in the superconductor, without invoking any role of proximity-induced superconductivity. The phenomena is important because it will ubiquitously coexist with any exotic new physics that may be present in this class of devices.
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Affiliation(s)
- Pankaj Mandal
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Nicolai Taufertshöfer
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Lukas Lunczer
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Martin P Stehno
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Charles Gould
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Laurens W Molenkamp
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
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9
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Mahler DM, Müller VL, Thienel C, Wiedenmann J, Beugeling W, Buhmann H, Molenkamp LW. Massive and Topological Surface States in Tensile-Strained HgTe. Nano Lett 2021; 21:9869-9874. [PMID: 34812638 DOI: 10.1021/acs.nanolett.1c02456] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Magneto-transport measurements on gated high-mobility heterostructures containing a 60 nm layer of tensile-strained HgTe, a three-dimensional topological insulator, show well-developed Hall quantization from surface states both in the n- as well as in the p-type regime. While the n-type behavior is due to transport in the topological surface state of the material, we find from 8-orbital k·p calculations that the p-type transport results from massive Volkov-Pankratov states. Their formation prevents the Dirac point and thus the p-conducting topological surface state from being accessible in transport experiments. This interpretation is supported by low-field magneto-transport experiments demonstrating the coexistence of n-conducting topological surface states and p-conducting Volkov-Pankratov states at the relevant gate voltages.
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Affiliation(s)
- David M Mahler
- Institute for Topological Insulators and Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Valentin L Müller
- Institute for Topological Insulators and Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Cornelius Thienel
- Institute for Topological Insulators and Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Jonas Wiedenmann
- Institute for Topological Insulators and Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Wouter Beugeling
- Institute for Topological Insulators and Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Hartmut Buhmann
- Institute for Topological Insulators and Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Laurens W Molenkamp
- Institute for Topological Insulators and Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
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10
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Zhang SB, Li CA, Peña-Benitez F, Surówka P, Moessner R, Molenkamp LW, Trauzettel B. Super-Resonant Transport of Topological Surface States Subjected to In-Plane Magnetic Fields. Phys Rev Lett 2021; 127:076601. [PMID: 34459623 DOI: 10.1103/physrevlett.127.076601] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2021] [Revised: 04/19/2021] [Accepted: 07/13/2021] [Indexed: 06/13/2023]
Abstract
Magnetic oscillations of Dirac surface states of topological insulators are typically expected to be associated with the formation of Landau levels or the Aharonov-Bohm effect. We instead study the conductance of Dirac surface states subjected to an in-plane magnetic field in the presence of a barrier potential. Strikingly, we find that, in the case of large barrier potentials, the surface states exhibit pronounced oscillations in the conductance when varying the magnetic field, in the absence of Landau levels or the Aharonov-Bohm effect. These novel magnetic oscillations are attributed to the emergence of super-resonant transport by tuning the magnetic field, in which many propagating modes cross the barrier with perfect transmission. In the case of small and moderate barrier potentials, we identify a positive magnetoconductance due to the increase of the Fermi surface by tilting the surface Dirac cone. Moreover, we show that for weak magnetic fields, the conductance displays a shifted sinusoidal dependence on the field direction with period π and phase shift determined by the tilting direction with respect to the field direction. Our predictions can be applied to various topological insulators, such as HgTe and Bi_{2}Se_{3}, and provide important insights into exploring and understanding exotic magnetotransport properties of topological surface states.
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Affiliation(s)
- Song-Bo Zhang
- Institut für Theoretische Physik und Astrophysik, Universität Würzburg, 97074 Würzburg, Germany
| | - Chang-An Li
- Institut für Theoretische Physik und Astrophysik, Universität Würzburg, 97074 Würzburg, Germany
| | - Francisco Peña-Benitez
- Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzer Strasse 38, 01187 Dresden, Germany
- Würzburg-Dresden Cluster of Excellence ct.qmat, Germany
| | - Piotr Surówka
- Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzer Strasse 38, 01187 Dresden, Germany
- Würzburg-Dresden Cluster of Excellence ct.qmat, Germany
- Department of Theoretical Physics, Wrocław University of Science and Technology, 50-370 Wrocław, Poland
| | - Roderich Moessner
- Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzer Strasse 38, 01187 Dresden, Germany
- Würzburg-Dresden Cluster of Excellence ct.qmat, Germany
| | - Laurens W Molenkamp
- Würzburg-Dresden Cluster of Excellence ct.qmat, Germany
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Max Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany
| | - Björn Trauzettel
- Institut für Theoretische Physik und Astrophysik, Universität Würzburg, 97074 Würzburg, Germany
- Würzburg-Dresden Cluster of Excellence ct.qmat, Germany
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11
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Müller VL, Yan Y, Kashuba O, Trauzettel B, Abdelghany M, Kleinlein J, Beugeling W, Buhmann H, Molenkamp LW. Electron-Hole Scattering Limited Transport of Dirac Fermions in a Topological Insulator. Nano Lett 2021; 21:5195-5200. [PMID: 34115500 DOI: 10.1021/acs.nanolett.1c01271] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
We have experimentally investigated the effect of electron temperature on transport in the two-dimensional Dirac surface states of the three-dimensional topological insulator HgTe. We have found that around the minimal conductivity point, where both electrons and holes are present, heating the carriers with a DC current results in a nonmonotonic differential resistance of narrow channels. We have shown that the observed initial increase in resistance can be attributed to electron-hole scattering, while the decrease follows naturally from the change in Fermi energy of the charge carriers. Both effects are governed dominantly by a van Hove singularity in the bulk valence band. The results demonstrate the importance of interband electron-hole scattering in the transport properties of topological insulators.
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Affiliation(s)
- Valentin L Müller
- Institute for Topological Insulators and Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Yuan Yan
- Institute for Topological Insulators and Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Oleksiy Kashuba
- Theoretische Physik IV, Institut für Theoretische Physik und Astrophysik, Universität Würzburg, 97074 Würzburg, Germany
| | - Björn Trauzettel
- Theoretische Physik IV, Institut für Theoretische Physik und Astrophysik, Universität Würzburg, 97074 Würzburg, Germany
| | - Mohamed Abdelghany
- Institute for Topological Insulators and Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Johannes Kleinlein
- Institute for Topological Insulators and Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Wouter Beugeling
- Institute for Topological Insulators and Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Hartmut Buhmann
- Institute for Topological Insulators and Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Laurens W Molenkamp
- Institute for Topological Insulators and Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
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12
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Shamim S, Beugeling W, Shekhar P, Bendias K, Lunczer L, Kleinlein J, Buhmann H, Molenkamp LW. Quantized spin Hall conductance in a magnetically doped two dimensional topological insulator. Nat Commun 2021; 12:3193. [PMID: 34045456 PMCID: PMC8160016 DOI: 10.1038/s41467-021-23262-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Accepted: 04/21/2021] [Indexed: 11/22/2022] Open
Abstract
Soon after the discovery of the quantum spin Hall effect, it has been predicted that a magnetic impurity in the presence of strong Coulomb interactions will destroy the quantum spin Hall effect. However, the fate of the quantum spin Hall effect in the presence of magnetic impurities has not yet been experimentally investigated. Here, we report the successful experimental demonstration of a quantized spin Hall resistance in HgTe quantum wells dilutely alloyed with magnetic Mn atoms. These quantum wells exhibit an inverted band structure that is very similar to that of the undoped material. Micron sized devices of (Hg,Mn)Te quantum well (in the topological phase) show a quantized spin Hall resistance of h/2e2 at low temperatures and zero magnetic field. At finite temperatures, we observe signatures of the Kondo effect due to interaction between the helical edge channels and magnetic impurities. Our work lays the foundation for future investigations of magnetically doped quantum spin Hall materials towards the realization of chiral Majorana fermions. The quantum spin Hall effect is expected not to survive the presence of magnetic impurities. Here, authors report full quantization at very low temperatures in HgTe quantum wells alloyed with a few percent of magnetic Mn atoms, due to Kondo screening.
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Affiliation(s)
- Saquib Shamim
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany. .,Institute for Topological Insulators, Universität Würzburg, Am Hubland, Würzburg, Germany.
| | - Wouter Beugeling
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany.,Institute for Topological Insulators, Universität Würzburg, Am Hubland, Würzburg, Germany
| | - Pragya Shekhar
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany.,Institute for Topological Insulators, Universität Würzburg, Am Hubland, Würzburg, Germany
| | - Kalle Bendias
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany.,Institute for Topological Insulators, Universität Würzburg, Am Hubland, Würzburg, Germany
| | - Lukas Lunczer
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany.,Institute for Topological Insulators, Universität Würzburg, Am Hubland, Würzburg, Germany
| | - Johannes Kleinlein
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany.,Institute for Topological Insulators, Universität Würzburg, Am Hubland, Würzburg, Germany
| | - Hartmut Buhmann
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany.,Institute for Topological Insulators, Universität Würzburg, Am Hubland, Würzburg, Germany
| | - Laurens W Molenkamp
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany. .,Institute for Topological Insulators, Universität Würzburg, Am Hubland, Würzburg, Germany.
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13
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Shamim S, Beugeling W, Böttcher J, Shekhar P, Budewitz A, Leubner P, Lunczer L, Hankiewicz EM, Buhmann H, Molenkamp LW. Emergent quantum Hall effects below 50 mT in a two-dimensional topological insulator. Sci Adv 2020; 6:eaba4625. [PMID: 32637611 PMCID: PMC7314521 DOI: 10.1126/sciadv.aba4625] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2019] [Accepted: 05/08/2020] [Indexed: 06/05/2023]
Abstract
The realization of the quantum spin Hall effect in HgTe quantum wells has led to the development of topological materials, which, in combination with magnetism and superconductivity, are predicted to host chiral Majorana fermions. However, the large magnetization in conventional quantum anomalous Hall systems makes it challenging to induce superconductivity. Here, we report two different emergent quantum Hall effects in (Hg,Mn)Te quantum wells. First, a previously unidentified quantum Hall state emerges from the quantum spin Hall state at an exceptionally low magnetic field of ~50 mT. Second, tuning toward the bulk p-regime, we resolve quantum Hall plateaus at fields as low as 20 to 30 mT, where transport is dominated by a van Hove singularity in the valence band. These emergent quantum Hall phenomena rely critically on the topological band structure of HgTe, and their occurrence at very low fields makes them an ideal candidate for realizing chiral Majorana fermions.
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Affiliation(s)
- Saquib Shamim
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Wouter Beugeling
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Jan Böttcher
- Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Pragya Shekhar
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Andreas Budewitz
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Philipp Leubner
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Lukas Lunczer
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Ewelina M. Hankiewicz
- Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Hartmut Buhmann
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Laurens W. Molenkamp
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
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14
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Dartiailh MC, Hartinger S, Gourmelon A, Bendias K, Bartolomei H, Kamata H, Berroir JM, Fève G, Plaçais B, Lunczer L, Schlereth R, Buhmann H, Molenkamp LW, Bocquillon E. Dynamical Separation of Bulk and Edge Transport in HgTe-Based 2D Topological Insulators. Phys Rev Lett 2020; 124:076802. [PMID: 32142329 DOI: 10.1103/physrevlett.124.076802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2019] [Accepted: 01/13/2020] [Indexed: 06/10/2023]
Abstract
Topological effects in edge states are clearly visible on short lengths only, thus largely impeding their studies. On larger distances, one may be able to dynamically enhance topological signatures by exploiting the high mobility of edge states with respect to bulk carriers. Our work on microwave spectroscopy highlights the response of the edges which host very mobile carriers, while bulk carriers are drastically slowed down in the gap. Though the edges are denser than expected, we establish that charge relaxation occurs on short timescales and suggest that edge states can be addressed selectively on timescales over which bulk carriers are frozen.
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Affiliation(s)
- Matthieu C Dartiailh
- Laboratoire de Physique de l'École Normale Supérieure, ENS, PSL Research University, CNRS, Sorbonne Université, Université de Paris, 24 rue Lhomond, 75231 Paris Cedex 05, France
| | - Simon Hartinger
- Physikalisches Institut (EP3), Am Hubland, Universität Würzburg, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, Universität Würzburg, D-97074 Würzburg, Germany
| | - Alexandre Gourmelon
- Laboratoire de Physique de l'École Normale Supérieure, ENS, PSL Research University, CNRS, Sorbonne Université, Université de Paris, 24 rue Lhomond, 75231 Paris Cedex 05, France
| | - Kalle Bendias
- Physikalisches Institut (EP3), Am Hubland, Universität Würzburg, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, Universität Würzburg, D-97074 Würzburg, Germany
| | - Hugo Bartolomei
- Laboratoire de Physique de l'École Normale Supérieure, ENS, PSL Research University, CNRS, Sorbonne Université, Université de Paris, 24 rue Lhomond, 75231 Paris Cedex 05, France
| | - Hiroshi Kamata
- Laboratoire de Physique de l'École Normale Supérieure, ENS, PSL Research University, CNRS, Sorbonne Université, Université de Paris, 24 rue Lhomond, 75231 Paris Cedex 05, France
| | - Jean-Marc Berroir
- Laboratoire de Physique de l'École Normale Supérieure, ENS, PSL Research University, CNRS, Sorbonne Université, Université de Paris, 24 rue Lhomond, 75231 Paris Cedex 05, France
| | - Gwendal Fève
- Laboratoire de Physique de l'École Normale Supérieure, ENS, PSL Research University, CNRS, Sorbonne Université, Université de Paris, 24 rue Lhomond, 75231 Paris Cedex 05, France
| | - Bernard Plaçais
- Laboratoire de Physique de l'École Normale Supérieure, ENS, PSL Research University, CNRS, Sorbonne Université, Université de Paris, 24 rue Lhomond, 75231 Paris Cedex 05, France
| | - Lukas Lunczer
- Physikalisches Institut (EP3), Am Hubland, Universität Würzburg, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, Universität Würzburg, D-97074 Würzburg, Germany
| | - Raimund Schlereth
- Physikalisches Institut (EP3), Am Hubland, Universität Würzburg, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, Universität Würzburg, D-97074 Würzburg, Germany
| | - Hartmut Buhmann
- Physikalisches Institut (EP3), Am Hubland, Universität Würzburg, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, Universität Würzburg, D-97074 Würzburg, Germany
| | - Laurens W Molenkamp
- Physikalisches Institut (EP3), Am Hubland, Universität Würzburg, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, Universität Würzburg, D-97074 Würzburg, Germany
| | - Erwann Bocquillon
- Laboratoire de Physique de l'École Normale Supérieure, ENS, PSL Research University, CNRS, Sorbonne Université, Université de Paris, 24 rue Lhomond, 75231 Paris Cedex 05, France
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15
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Kayyalha M, Xiao D, Zhang R, Shin J, Jiang J, Wang F, Zhao YF, Xiao R, Zhang L, Fijalkowski KM, Mandal P, Winnerlein M, Gould C, Li Q, Molenkamp LW, Chan MHW, Samarth N, Chang CZ. Absence of evidence for chiral Majorana modes in quantum anomalous Hall-superconductor devices. Science 2020; 367:64-67. [DOI: 10.1126/science.aax6361] [Citation(s) in RCA: 70] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2019] [Accepted: 11/07/2019] [Indexed: 11/02/2022]
Affiliation(s)
- Morteza Kayyalha
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Di Xiao
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Ruoxi Zhang
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Jaeho Shin
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Jue Jiang
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Fei Wang
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Yi-Fan Zhao
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Run Xiao
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Ling Zhang
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Kajetan M. Fijalkowski
- Faculty for Physics and Astronomy (EP3), University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Pankaj Mandal
- Faculty for Physics and Astronomy (EP3), University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Martin Winnerlein
- Faculty for Physics and Astronomy (EP3), University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Charles Gould
- Faculty for Physics and Astronomy (EP3), University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Qi Li
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Laurens W. Molenkamp
- Faculty for Physics and Astronomy (EP3), University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Moses H. W. Chan
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Nitin Samarth
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Cui-Zu Chang
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
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16
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Böttcher J, Tutschku C, Molenkamp LW, Hankiewicz EM. Survival of the Quantum Anomalous Hall Effect in Orbital Magnetic Fields as a Consequence of the Parity Anomaly. Phys Rev Lett 2019; 123:226602. [PMID: 31868409 DOI: 10.1103/physrevlett.123.226602] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2019] [Indexed: 06/10/2023]
Abstract
Recent experimental progress in condensed matter physics enables the observation of signatures of the parity anomaly in two-dimensional Dirac-like materials. Using effective field theories and analyzing band structures in external out-of-plane magnetic fields (orbital fields), we show that topological properties of quantum anomalous Hall (QAH) insulators are related to the parity anomaly. We demonstrate that the QAH phase survives in orbital fields, violates the Onsager relation, and can be therefore distinguished from a quantum Hall (QH) phase. As a fingerprint of the QAH phase in increasing orbital fields, we predict a transition from a quantized Hall plateau with σ_{xy}=-e^{2}/h to a not perfectly quantized plateau, caused by scattering processes between counterpropagating QH and QAH edge states. This transition can be especially important in paramagnetic QAH insulators, such as (Hg,Mn)Te/CdTe quantum wells, in which exchange interaction and orbital fields compete.
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Affiliation(s)
- Jan Böttcher
- Institut für theoretische Physik (TP4) and Würzburg-Dresden Cluster of Excellence ct.qmat, Universität Würzburg, 97074 Würzburg, Germany
| | - Christian Tutschku
- Institut für theoretische Physik (TP4) and Würzburg-Dresden Cluster of Excellence ct.qmat, Universität Würzburg, 97074 Würzburg, Germany
| | - Laurens W Molenkamp
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - E M Hankiewicz
- Institut für theoretische Physik (TP4) and Würzburg-Dresden Cluster of Excellence ct.qmat, Universität Würzburg, 97074 Würzburg, Germany
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17
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Lunczer L, Leubner P, Endres M, Müller VL, Brüne C, Buhmann H, Molenkamp LW. Approaching Quantization in Macroscopic Quantum Spin Hall Devices through Gate Training. Phys Rev Lett 2019; 123:047701. [PMID: 31491275 DOI: 10.1103/physrevlett.123.047701] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2019] [Revised: 04/24/2019] [Indexed: 06/10/2023]
Abstract
Quantum spin Hall edge channels hold great promise as dissipationless one-dimensional conductors. However, the ideal quantized conductance of 2e^{2}/h is only found in very short channels-in contradiction with the expected protection against backscattering of the topological insulator state. In this Letter we show that enhancing the band gap does not improve quantization. When we instead alter the potential landscape by charging trap states in the gate dielectric using gate training, we approach conductance quantization for macroscopically long channels. Effectively, the scattering length increases to 175 μm, more than 1 order of magnitude longer than in previous works for HgTe-based quantum wells. Our experiments show that the distortion of the potential landscape by impurities, leading to puddle formation in the narrow gap material, is the major obstacle for observing undisturbed quantum spin Hall edge channel transport.
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Affiliation(s)
- Lukas Lunczer
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Philipp Leubner
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Martin Endres
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Valentin L Müller
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Christoph Brüne
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Hartmut Buhmann
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Laurens W Molenkamp
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
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18
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Hajer J, Kessel M, Brüne C, Stehno MP, Buhmann H, Molenkamp LW. Proximity-Induced Superconductivity in CdTe-HgTe Core-Shell Nanowires. Nano Lett 2019; 19:4078-4082. [PMID: 31120766 DOI: 10.1021/acs.nanolett.9b01472] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
In this Letter we report on proximity superconductivity induced in CdTe-HgTe core-shell nanowires, a quasi-one-dimensional heterostructure of the topological insulator HgTe. We demonstrate a Josephson supercurrent in our nanowires contacted with superconducting Al leads. The observation of a sizable Ic Rn product, a positive excess current, and multiple Andreev reflections up to fourth order further indicate a high interface quality of the junctions.
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Affiliation(s)
- Jan Hajer
- Institute for Topological Insulators and Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland , DE-97074 Würzburg , Germany
| | - Maximilian Kessel
- Institute for Topological Insulators and Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland , DE-97074 Würzburg , Germany
| | - Christoph Brüne
- Institute for Topological Insulators and Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland , DE-97074 Würzburg , Germany
| | - Martin P Stehno
- Institute for Topological Insulators and Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland , DE-97074 Würzburg , Germany
| | - Hartmut Buhmann
- Institute for Topological Insulators and Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland , DE-97074 Würzburg , Germany
| | - Laurens W Molenkamp
- Institute for Topological Insulators and Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland , DE-97074 Würzburg , Germany
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19
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Ren H, Pientka F, Hart S, Pierce AT, Kosowsky M, Lunczer L, Schlereth R, Scharf B, Hankiewicz EM, Molenkamp LW, Halperin BI, Yacoby A. Topological superconductivity in a phase-controlled Josephson junction. Nature 2019; 569:93-98. [PMID: 31019296 DOI: 10.1038/s41586-019-1148-9] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Accepted: 02/14/2019] [Indexed: 11/09/2022]
Abstract
Topological superconductors can support localized Majorana states at their boundaries1-5. These quasi-particle excitations obey non-Abelian statistics that can be used to encode and manipulate quantum information in a topologically protected manner6,7. Although signatures of Majorana bound states have been observed in one-dimensional systems, there is an ongoing effort to find alternative platforms that do not require fine-tuning of parameters and can be easily scaled to large numbers of states8-21. Here we present an experimental approach towards a two-dimensional architecture of Majorana bound states. Using a Josephson junction made of a HgTe quantum well coupled to thin-film aluminium, we are able to tune the transition between a trivial and a topological superconducting state by controlling the phase difference across the junction and applying an in-plane magnetic field22. We determine the topological state of the resulting superconductor by measuring the tunnelling conductance at the edge of the junction. At low magnetic fields, we observe a minimum in the tunnelling spectra near zero bias, consistent with a trivial superconductor. However, as the magnetic field increases, the tunnelling conductance develops a zero-bias peak, which persists over a range of phase differences that expands systematically with increasing magnetic field. Our observations are consistent with theoretical predictions for this system and with full quantum mechanical numerical simulations performed on model systems with similar dimensions and parameters. Our work establishes this system as a promising platform for realizing topological superconductivity and for creating and manipulating Majorana modes and probing topological superconducting phases in two-dimensional systems.
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Affiliation(s)
- Hechen Ren
- Department of Physics, Harvard University, Cambridge, MA, USA.,Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, CA, USA
| | - Falko Pientka
- Department of Physics, Harvard University, Cambridge, MA, USA.,Max-Planck-Institut für Physik komplexer Systeme, Dresden, Germany
| | - Sean Hart
- Department of Physics, Harvard University, Cambridge, MA, USA.,IBM T. J. Watson Research Center, Yorktown Heights, NY, USA
| | - Andrew T Pierce
- Department of Physics, Harvard University, Cambridge, MA, USA
| | | | - Lukas Lunczer
- Physikalisches Institut (EP3) and Institute for Topological Insulators, Universität Würzburg, Würzburg, Germany
| | - Raimund Schlereth
- Physikalisches Institut (EP3) and Institute for Topological Insulators, Universität Würzburg, Würzburg, Germany
| | - Benedikt Scharf
- Institut für Theoretische Physik und Astrophysik and Würzburg-Dresden Cluster of Excellence ct.qmat, Universität Würzburg, Würzburg, Germany
| | - Ewelina M Hankiewicz
- Institut für Theoretische Physik und Astrophysik and Würzburg-Dresden Cluster of Excellence ct.qmat, Universität Würzburg, Würzburg, Germany
| | | | | | - Amir Yacoby
- Department of Physics, Harvard University, Cambridge, MA, USA.
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20
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Bendias K, Shamim S, Herrmann O, Budewitz A, Shekhar P, Leubner P, Kleinlein J, Bocquillon E, Buhmann H, Molenkamp LW. High Mobility HgTe Microstructures for Quantum Spin Hall Studies. Nano Lett 2018; 18:4831-4836. [PMID: 29975844 DOI: 10.1021/acs.nanolett.8b01405] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The topic of two-dimensional topological insulators has blossomed after the first observation of the quantum spin Hall (QSH) effect in HgTe quantum wells. However, studies have been hindered by the relative fragility of the edge states. Their stability has been a subject of both theoretical and experimental investigation in the past decade. Here, we present a new generation of high quality (Cd,Hg)Te/HgTe-structures based on a new chemical etching method. From magnetotransport measurements on macro- and microscopic Hall bars, we extract electron mobilities μ up to about 400 × 103 cm2/(V s), and the mean free path λmfp becomes comparable to the sample dimensions. The Hall bars show quantized spin Hall conductance, which is remarkably stable up to 15 K. The clean and robust edge states allow us to fabricate high quality side-contacted Josephson junctions, which are significant in the context of topological superconductivity. Our results open up new avenues for fundamental research on QSH effect as well as potential applications in spintronics and topological quantum computation.
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Affiliation(s)
- Kalle Bendias
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
| | - Saquib Shamim
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
| | - Oliver Herrmann
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
| | - Andreas Budewitz
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
| | - Pragya Shekhar
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
| | - Philipp Leubner
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
| | - Johannes Kleinlein
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
| | - Erwann Bocquillon
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
- Laboratoire Pierre Aigrain, Ecole Normale Supériere, PSL Research University, Sorbonne Université, Université Paris Diderot, Sorbonne Paris Cité, CNRS , 24 rue Lhomond , 75005 Paris , France
| | - Hartmut Buhmann
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
| | - Laurens W Molenkamp
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
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21
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Calvo MR, de Juan F, Ilan R, Fox EJ, Bestwick AJ, Mühlbauer M, Wang J, Ames C, Leubner P, Brüne C, Zhang SC, Buhmann H, Molenkamp LW, Goldhaber-Gordon D. Interplay of Chiral and Helical States in a Quantum Spin Hall Insulator Lateral Junction. Phys Rev Lett 2017; 119:226401. [PMID: 29286805 DOI: 10.1103/physrevlett.119.226401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Indexed: 06/07/2023]
Abstract
We study the electronic transport across an electrostatically gated lateral junction in a HgTe quantum well, a canonical 2D topological insulator, with and without an applied magnetic field. We control the carrier density inside and outside a junction region independently and hence tune the number and nature of 1D edge modes propagating in each of those regions. Outside the bulk gap, the magnetic field drives the system to the quantum Hall regime, and chiral states propagate at the edge. In this regime, we observe fractional plateaus that reflect the equilibration between 1D chiral modes across the junction. As the carrier density approaches zero in the central region and at moderate fields, we observe oscillations in the resistance that we attribute to Fabry-Perot interference in the helical states, enabled by the broken time reversal symmetry. At higher fields, those oscillations disappear, in agreement with the expected absence of helical states when band inversion is lifted.
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Affiliation(s)
- M R Calvo
- Department of Physics, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
- CIC nanoGUNE, 20018 Donostia-San Sebastian, Spain
- Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain
| | - F de Juan
- Department of Physics, University of California, Berkeley, California 94720, USA
| | - R Ilan
- Department of Physics, University of California, Berkeley, California 94720, USA
- Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
| | - E J Fox
- Department of Physics, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
| | - A J Bestwick
- Department of Physics, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
| | - M Mühlbauer
- Physikalisches Institut (EP3) and Röntgen Center for Complex Material Systems, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - J Wang
- Department of Physics, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
| | - C Ames
- Physikalisches Institut (EP3) and Röntgen Center for Complex Material Systems, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - P Leubner
- Physikalisches Institut (EP3) and Röntgen Center for Complex Material Systems, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - C Brüne
- Physikalisches Institut (EP3) and Röntgen Center for Complex Material Systems, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - S C Zhang
- Department of Physics, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
| | - H Buhmann
- Physikalisches Institut (EP3) and Röntgen Center for Complex Material Systems, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - L W Molenkamp
- Physikalisches Institut (EP3) and Röntgen Center for Complex Material Systems, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - D Goldhaber-Gordon
- Department of Physics, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
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22
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Leighton C, Molenkamp LW, Ben-Naim E, Forrest S. Editorial: Materials Research in the Physical Review Journals. Phys Rev E 2017; 96:020001. [PMID: 28950634 DOI: 10.1103/physreve.96.020001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2017] [Indexed: 11/07/2022]
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23
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Leubner P, Lunczer L, Brüne C, Buhmann H, Molenkamp LW. Publisher's Note: Strain Engineering of the Band Gap of HgTe Quantum Wells Using Superlattice Virtual Substrates [Phys. Rev. Lett. 117, 086403 (2016)]. Phys Rev Lett 2017; 119:079901. [PMID: 28949681 DOI: 10.1103/physrevlett.119.079901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2017] [Indexed: 06/07/2023]
Abstract
This corrects the article DOI: 10.1103/PhysRevLett.117.086403.
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24
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Grauer S, Fijalkowski KM, Schreyeck S, Winnerlein M, Brunner K, Thomale R, Gould C, Molenkamp LW. Scaling of the Quantum Anomalous Hall Effect as an Indicator of Axion Electrodynamics. Phys Rev Lett 2017; 118:246801. [PMID: 28665643 DOI: 10.1103/physrevlett.118.246801] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Indexed: 06/07/2023]
Abstract
We report on the scaling behavior of V-doped (Bi,Sb)_{2}Te_{3} samples in the quantum anomalous Hall regime for samples of various thickness. While previous quantum anomalous Hall measurements showed the same scaling as expected from a two-dimensional integer quantum Hall state, we observe a dimensional crossover to three spatial dimensions as a function of layer thickness. In the limit of a sufficiently thick layer, we find scaling behavior matching the flow diagram of two parallel conducting topological surface states of a three-dimensional topological insulator each featuring a fractional shift of 1/2e^{2}/h in the flow diagram Hall conductivity, while we recover the expected integer quantum Hall behavior for thinner layers. This constitutes the observation of a distinct type of quantum anomalous Hall effect, resulting from 1/2e^{2}/h Hall conductance quantization of three-dimensional topological insulator surface states, in an experiment which does not require decomposition of the signal to separate the contribution of two surfaces. This provides a possible experimental link between quantum Hall physics and axion electrodynamics.
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Affiliation(s)
- S Grauer
- Faculty for Physics and Astronomy (EP3 and TP1), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - K M Fijalkowski
- Faculty for Physics and Astronomy (EP3 and TP1), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - S Schreyeck
- Faculty for Physics and Astronomy (EP3 and TP1), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - M Winnerlein
- Faculty for Physics and Astronomy (EP3 and TP1), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - K Brunner
- Faculty for Physics and Astronomy (EP3 and TP1), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - R Thomale
- Faculty for Physics and Astronomy (EP3 and TP1), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - C Gould
- Faculty for Physics and Astronomy (EP3 and TP1), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - L W Molenkamp
- Faculty for Physics and Astronomy (EP3 and TP1), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
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25
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Bocquillon E, Deacon RS, Wiedenmann J, Leubner P, Klapwijk TM, Brüne C, Ishibashi K, Buhmann H, Molenkamp LW. Gapless Andreev bound states in the quantum spin Hall insulator HgTe. Nat Nanotechnol 2017; 12:137-143. [PMID: 27570940 DOI: 10.1038/nnano.2016.159] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Accepted: 07/21/2016] [Indexed: 05/12/2023]
Abstract
In recent years, Majorana physics has attracted considerable attention because of exotic new phenomena and its prospects for fault-tolerant topological quantum computation. To this end, one needs to engineer the interplay between superconductivity and electronic properties in a topological insulator, but experimental work remains scarce and ambiguous. Here, we report experimental evidence for topological superconductivity induced in a HgTe quantum well, a 2D topological insulator that exhibits the quantum spin Hall (QSH) effect. The a.c. Josephson effect demonstrates that the supercurrent has a 4π periodicity in the superconducting phase difference, as indicated by a doubling of the voltage step for multiple Shapiro steps. In addition, this response like that of a superconducting quantum interference device to a perpendicular magnetic field shows that the 4π-periodic supercurrent originates from states located on the edges of the junction. Both features appear strongest towards the QSH regime, and thus provide evidence for induced topological superconductivity in the QSH edge states.
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Affiliation(s)
- Erwann Bocquillon
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Russell S Deacon
- Advanced Device Laboratory, RIKEN, 2-1 Hirosawa, Wako-shi, Saitama, 351-0198, Japan
- Center for Emergent Matter Science, RIKEN, 2-1 Hirosawa, Wako-shi, Saitama, 351-0198, Japan
| | - Jonas Wiedenmann
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Philipp Leubner
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Teunis M Klapwijk
- Faculty of Applied Sciences, Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
| | - Christoph Brüne
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Koji Ishibashi
- Advanced Device Laboratory, RIKEN, 2-1 Hirosawa, Wako-shi, Saitama, 351-0198, Japan
- Center for Emergent Matter Science, RIKEN, 2-1 Hirosawa, Wako-shi, Saitama, 351-0198, Japan
| | - Hartmut Buhmann
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Laurens W Molenkamp
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
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26
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Leubner P, Lunczer L, Brüne C, Buhmann H, Molenkamp LW. Strain Engineering of the Band Gap of HgTe Quantum Wells Using Superlattice Virtual Substrates. Phys Rev Lett 2016; 117:086403. [PMID: 27588871 DOI: 10.1103/physrevlett.117.086403] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2016] [Indexed: 06/06/2023]
Abstract
The HgTe quantum well (QW) is a well-characterized two-dimensional topological insulator (2D TI). Its band gap is relatively small (typically on the order of 10 meV), which restricts the observation of purely topological conductance to low temperatures. Here, we utilize the strain dependence of the band structure of HgTe QWs to address this limitation. We use CdTe-Cd_{0.5}Zn_{0.5}Te strained-layer superlattices on GaAs as virtual substrates with adjustable lattice constant to control the strain of the QW. We present magnetotransport measurements, which demonstrate a transition from a semimetallic to a 2D-TI regime in wide QWs, when the strain is changed from tensile to compressive. Most notably, we demonstrate a much enhanced energy gap of 55 meV in heavily compressively strained QWs. This value exceeds the highest possible gap on common II-VI substrates by a factor of 2-3, and extends the regime where the topological conductance prevails to much higher temperatures.
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Affiliation(s)
- Philipp Leubner
- Experimentelle Physik III, Physikalisches Institut, Universitüt Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Lukas Lunczer
- Experimentelle Physik III, Physikalisches Institut, Universitüt Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Christoph Brüne
- Experimentelle Physik III, Physikalisches Institut, Universitüt Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Hartmut Buhmann
- Experimentelle Physik III, Physikalisches Institut, Universitüt Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Laurens W Molenkamp
- Experimentelle Physik III, Physikalisches Institut, Universitüt Würzburg, Am Hubland, D-97074 Würzburg, Germany
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27
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Schreyeck S, Brunner K, Kirchner A, Bass U, Grauer S, Schumacher C, Gould C, Karczewski G, Geurts J, Molenkamp LW. Kinetic limitation of chemical ordering in Bi2Te3-x Se x layers grown by molecular beam epitaxy. J Phys Condens Matter 2016; 28:145002. [PMID: 26962934 DOI: 10.1088/0953-8984/28/14/145002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We study the chemical ordering in Bi2Te3-x Se x grown by molecular beam epitaxy on Si substrates. We produce films in the full composition range from x = 0 to 3, and determine their material properties using energy dispersive x-ray spectroscopy, x-ray diffraction and Raman spectroscopy. By fitting the parameters of a kinetic growth model to these results, we obtain a consistent description of growth at a microscopic level. Our main finding is that despite the incorporation of Se in the central layer being much more probable than that of Te, the formation of a fully ordered Te-Bi-Se-Bi-Te layer is prevented by kinetic of the growth process. Indeed, the Se concentration in the central layer of Bi2Te2Se1 reaches a maximum of only ≈ 75% even under ideal growth conditions. A second finding of our work is that the intensity ratio of the 0 0 12 and 0 0 6 x-ray reflections serves as an experimentally accessible quantitative measure of the degree of ordering in these films.
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Affiliation(s)
- S Schreyeck
- Physikalisches Institut, Experimentelle Physik 3 and Wilhelm-Conrad Röntgen-Research Center for Complex Material Systems, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
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28
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Thierschmann H, Sánchez R, Sothmann B, Arnold F, Heyn C, Hansen W, Buhmann H, Molenkamp LW. Three-terminal energy harvester with coupled quantum dots. Nat Nanotechnol 2015; 10:854-8. [PMID: 26280407 DOI: 10.1038/nnano.2015.176] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2015] [Accepted: 07/08/2015] [Indexed: 05/11/2023]
Abstract
Rectification of thermal fluctuations in mesoscopic conductors is the key idea behind recent attempts to build nanoscale thermoelectric energy harvesters to convert heat into useful electric power. So far, most concepts have made use of the Seebeck effect in a two-terminal geometry, where heat and charge are both carried by the same particles. Here, we experimentally demonstrate the working principle of a new kind of energy harvester, proposed recently, using two capacitively coupled quantum dots. We show that, due to the novel three-terminal design of our device, which spatially separates the heat reservoir from the conductor circuit, the directions of charge and heat flow become decoupled. This enables us to manipulate the direction of the generated charge current by means of external gate voltages while leaving the direction of heat flow unaffected. Our results pave the way for a new generation of multi-terminal nanoscale heat engines.
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Affiliation(s)
- Holger Thierschmann
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, Würzburg D-97074, Germany
| | - Rafael Sánchez
- Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, Madrid 28049, Spain
| | - Björn Sothmann
- Département de Physique Théorique, Université de Genève, Genève 4 CH-1211, Switzerland
| | - Fabian Arnold
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, Würzburg D-97074, Germany
| | - Christian Heyn
- Institute of Applied Physics, University of Hamburg, Jungiusstrasse 11, Hamburg D-20355, Germany
| | - Wolfgang Hansen
- Institute of Applied Physics, University of Hamburg, Jungiusstrasse 11, Hamburg D-20355, Germany
| | - Hartmut Buhmann
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, Würzburg D-97074, Germany
| | - Laurens W Molenkamp
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, Würzburg D-97074, Germany
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29
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Orlita M, Piot BA, Martinez G, Kumar NKS, Faugeras C, Potemski M, Michel C, Hankiewicz EM, Brauner T, Drašar Č, Schreyeck S, Grauer S, Brunner K, Gould C, Brüne C, Molenkamp LW. Magneto-optics of massive dirac fermions in bulk Bi2Se3. Phys Rev Lett 2015; 114:186401. [PMID: 26001011 DOI: 10.1103/physrevlett.114.186401] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2015] [Indexed: 05/27/2023]
Abstract
We report on magneto-optical studies of Bi2Se3, a representative member of the 3D topological insulator family. Its electronic states in bulk are shown to be well described by a simple Dirac-type Hamiltonian for massive particles with only two parameters: the fundamental band gap and the band velocity. In a magnetic field, this model implies a unique property-spin splitting equal to twice the cyclotron energy: Es=2Ec. This explains the extensive magnetotransport studies concluding a fortuitous degeneracy of the spin and orbital split Landau levels in this material. The Es=2Ec match differentiates the massive Dirac electrons in bulk Bi2Se3 from those in quantum electrodynamics, for which Es=Ec always holds.
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Affiliation(s)
- M Orlita
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UJF-UPS-INSA, 25, avenue des Martyrs, 38042 Grenoble, France
- Institute of Physics, Charles University in Prague, CZ-12116 Prague, Czech Republic
| | - B A Piot
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UJF-UPS-INSA, 25, avenue des Martyrs, 38042 Grenoble, France
| | - G Martinez
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UJF-UPS-INSA, 25, avenue des Martyrs, 38042 Grenoble, France
| | - N K Sampath Kumar
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UJF-UPS-INSA, 25, avenue des Martyrs, 38042 Grenoble, France
| | - C Faugeras
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UJF-UPS-INSA, 25, avenue des Martyrs, 38042 Grenoble, France
| | - M Potemski
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UJF-UPS-INSA, 25, avenue des Martyrs, 38042 Grenoble, France
| | - C Michel
- Institute for Theoretical Physics, TP IV, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - E M Hankiewicz
- Institute for Theoretical Physics, TP IV, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - T Brauner
- Institute for Theoretical Physics, Vienna University of Technology, A-1040 Vienna, Austria
| | - Č Drašar
- Faculty of Chemical Technology, University of Pardubice, CZ-53210 Pardubice, Czech Republic
| | - S Schreyeck
- Physikalisches Institut (EP III), Universität Würzburg, D-97074 Würzburg, Germany
| | - S Grauer
- Physikalisches Institut (EP III), Universität Würzburg, D-97074 Würzburg, Germany
| | - K Brunner
- Physikalisches Institut (EP III), Universität Würzburg, D-97074 Würzburg, Germany
| | - C Gould
- Physikalisches Institut (EP III), Universität Würzburg, D-97074 Würzburg, Germany
| | - C Brüne
- Physikalisches Institut (EP III), Universität Würzburg, D-97074 Würzburg, Germany
| | - L W Molenkamp
- Physikalisches Institut (EP III), Universität Würzburg, D-97074 Würzburg, Germany
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30
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Karczewski G, Szot M, Kret S, Kowalczyk L, Chusnutdinow S, Wojtowicz T, Schreyeck S, Brunner K, Schumacher C, Molenkamp LW. Nanoscale morphology of multilayer PbTe/CdTe heterostructures and its effect on photoluminescence properties. Nanotechnology 2015; 26:135601. [PMID: 25751540 DOI: 10.1088/0957-4484/26/13/135601] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We study nanoscale morphology of PbTe/CdTe multilayer heterostuctures grown by molecular beam epitaxy on hybrid GaAs/CdTe (100) substrates. Nominally, the structures consist of 25 repetitions of subsequently deposited CdTe and PbTe layers with comparable thicknesses of 21 and 8 nm, respectively. However, the morphology of the resulting structures crucially depends on the growth temperature. The two-dimensional layered, superlattice-like character of the structures remains preserved only when grown at low substrate temperatures, such as 230 °C. The samples grown at the slightly elevated temperature of 270 °C undergo a morphological transformation to structures consisting of CdTe and PbTe pillars and columns oriented perpendicular to the substrate. Although the pillar-like objects are of various shapes and dimensions these structures exhibit exceptionally strong photoluminescence in the near infrared spectral region. At the higher growth temperature of 310 °C, PbTe and CdTe separate completely forming thick layers oriented longitudinally to the substrate plane. The observed topological transformations are driven by thermally activated atomic diffusion in the solid state phase. The solid state phase remains fully coherent during the processes. The observed topological transitions leading to the material separation in PbTe/CdTe system could be regarded as an analog of spinodal decomposition of an immiscible solid state solution and thus they can be qualitatively described by the Cahn-Hillard model as proposed by Groiss et al (2014 APL Mater. 2 012105).
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Affiliation(s)
- G Karczewski
- Institute of Physics, Polish Academy of Science, al. Lotników 32/46, 02-668 Warszawa, Poland
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31
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Sochnikov I, Maier L, Watson CA, Kirtley JR, Gould C, Tkachov G, Hankiewicz EM, Brüne C, Buhmann H, Molenkamp LW, Moler KA. Nonsinusoidal current-phase relationship in Josephson junctions from the 3D topological insulator HgTe. Phys Rev Lett 2015; 114:066801. [PMID: 25723235 DOI: 10.1103/physrevlett.114.066801] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2014] [Indexed: 05/22/2023]
Abstract
We use superconducting quantum interference device microscopy to characterize the current-phase relation (CPR) of Josephson junctions from the three-dimensional topological insulator HgTe (3D HgTe). We find clear skewness in the CPRs of HgTe junctions ranging in length from 200 to 600 nm. The skewness indicates that the Josephson current is predominantly carried by Andreev bound states with high transmittance, and the fact that the skewness persists in junctions that are longer than the mean free path suggests that the effect may be related to the helical nature of the Andreev bound states in the surface of HgTe. These experimental results suggest that the topological properties of the normal state can be inherited by the induced superconducting state, and that 3D HgTe is a promising material for realizing the many exciting proposals that require a topological superconductor.
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Affiliation(s)
- Ilya Sochnikov
- Department of Applied Physics, Stanford University, Stanford, California 94305, USA and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA
| | - Luis Maier
- Physikalisches Institut (EP3), University of Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Christopher A Watson
- Department of Applied Physics, Stanford University, Stanford, California 94305, USA and Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
| | - John R Kirtley
- Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA and Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
| | - Charles Gould
- Physikalisches Institut (EP3), University of Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Grigory Tkachov
- Institute for Theoretical Physics and Astrophysics, University of Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Ewelina M Hankiewicz
- Institute for Theoretical Physics and Astrophysics, University of Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Christoph Brüne
- Physikalisches Institut (EP3), University of Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Hartmut Buhmann
- Physikalisches Institut (EP3), University of Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Laurens W Molenkamp
- Physikalisches Institut (EP3), University of Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Kathryn A Moler
- Department of Applied Physics, Stanford University, Stanford, California 94305, USA and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA and Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
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32
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Mühlbauer M, Budewitz A, Büttner B, Tkachov G, Hankiewicz EM, Brüne C, Buhmann H, Molenkamp LW. One-dimensional weak antilocalization due to the berry phase in HgTe wires. Phys Rev Lett 2014; 112:146803. [PMID: 24766002 DOI: 10.1103/physrevlett.112.146803] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2013] [Indexed: 06/03/2023]
Abstract
We study the weak antilocalization (WAL) effect in the magnetoresistance of narrow HgTe wires fabricated in quantum wells with normal and inverted band ordering. Measurements at different gate voltages indicate that the WAL is only weakly affected by Rashba spin-orbit splitting and persists when the Rashba splitting is about zero. The WAL amplitude in wires with normal band ordering is an order of magnitude smaller than for wires with an inverted band structure. These observations are attributed to the Dirac-like dispersion of the energy bands in HgTe quantum wells. From the magnetic-field and temperature dependencies we extract the dephasing lengths and band Berry phases. The weaker WAL for samples with a normal band structure can be explained by a nonuniversal Berry phase which always exceeds π, the characteristic value for gapless Dirac fermions.
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Affiliation(s)
- M Mühlbauer
- Faculty of Physics and Astrophysics, University of Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - A Budewitz
- Faculty of Physics and Astrophysics, University of Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - B Büttner
- Faculty of Physics and Astrophysics, University of Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - G Tkachov
- Faculty of Physics and Astrophysics, University of Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - E M Hankiewicz
- Faculty of Physics and Astrophysics, University of Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - C Brüne
- Faculty of Physics and Astrophysics, University of Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - H Buhmann
- Faculty of Physics and Astrophysics, University of Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - L W Molenkamp
- Faculty of Physics and Astrophysics, University of Würzburg, Am Hubland, 97074 Würzburg, Germany
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33
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Landolt G, Schreyeck S, Eremeev SV, Slomski B, Muff S, Osterwalder J, Chulkov EV, Gould C, Karczewski G, Brunner K, Buhmann H, Molenkamp LW, Dil JH. Spin texture of Bi2Se3 thin films in the quantum tunneling limit. Phys Rev Lett 2014; 112:057601. [PMID: 24580629 DOI: 10.1103/physrevlett.112.057601] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2013] [Indexed: 06/03/2023]
Abstract
By means of spin- and angle-resolved photoelectron spectroscopy we studied the spin structure of thin films of the topological insulator Bi2Se3 grown on InP(111). For thicknesses below six quintuple layers the spin-polarized metallic topological surface states interact with each other via quantum tunneling and a gap opens. Our measurements show that the resulting surface states can be described by massive Dirac cones which are split in a Rashba-like manner due to the substrate induced inversion asymmetry. The inner and the outer Rashba branches have distinct localization in the top and the bottom part of the film, whereas the band apices are delocalized throughout the entire film. Supported by calculations, our observations help in the understanding of the evolution of the surface states at the topological phase transition and provide the groundwork for the realization of two-dimensional spintronic devices based on topological semiconductors.
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Affiliation(s)
- Gabriel Landolt
- Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland and Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen, Switzerland
| | - Steffen Schreyeck
- Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Sergey V Eremeev
- Institute of Strength Physics and Materials Science, Russian Academy of Sciences, Siberian Branch, Akademicheskiy prospekt 2/4, Tomsk, 634021 Russia and Tomsk State University, Tomsk, 634050 Russia
| | - Bartosz Slomski
- Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland and Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen, Switzerland
| | - Stefan Muff
- Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland and Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen, Switzerland and Institut de Physique de la Matière Condensée, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
| | - Jürg Osterwalder
- Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
| | - Evgueni V Chulkov
- Tomsk State University, Tomsk, 634050 Russia and Donostia International Physics Center (DIPC) and CFM-MPC, Centro Mixto CSIC-UPV/EHU, Departamento de Física de Materiales, UPV/EHU, 20080 San Sebastián, Spain
| | - Charles Gould
- Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Grzegorz Karczewski
- Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany and Institute of Physics, Polish Academy of Sciences, aleja Lotników 32/46, 02-668 Warsaw, Poland
| | - Karl Brunner
- Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Hartmut Buhmann
- Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Laurens W Molenkamp
- Physikalisches Institut, Experimentelle Physik III, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - J Hugo Dil
- Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland and Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen, Switzerland and Institut de Physique de la Matière Condensée, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
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34
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Henn T, Kiessling T, Ossau W, Molenkamp LW, Biermann K, Santos PV. Ultrafast supercontinuum fiber-laser based pump-probe scanning magneto-optical Kerr effect microscope for the investigation of electron spin dynamics in semiconductors at cryogenic temperatures with picosecond time and micrometer spatial resolution. Rev Sci Instrum 2013; 84:123903. [PMID: 24387442 DOI: 10.1063/1.4842276] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
We describe a two-color pump-probe scanning magneto-optical Kerr effect microscope which we have developed to investigate electron spin phenomena in semiconductors at cryogenic temperatures with picosecond time and micrometer spatial resolution. The key innovation of our microscope is the usage of an ultrafast "white light" supercontinuum fiber-laser source which provides access to the whole visible and near-infrared spectral range. Our Kerr microscope allows for the independent selection of the excitation and detection energy while avoiding the necessity to synchronize the pulse trains of two separate picosecond laser systems. The ability to independently tune the pump and probe wavelength enables the investigation of the influence of excitation energy on the optically induced electron spin dynamics in semiconductors. We demonstrate picosecond real-space imaging of the diffusive expansion of optically excited electron spin packets in a (110) GaAs quantum well sample to illustrate the capabilities of the instrument.
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Affiliation(s)
- T Henn
- Physikalisches Institut (EP3), Universität Würzburg, 97074 Würzburg, Germany
| | - T Kiessling
- Physikalisches Institut (EP3), Universität Würzburg, 97074 Würzburg, Germany
| | - W Ossau
- Physikalisches Institut (EP3), Universität Würzburg, 97074 Würzburg, Germany
| | - L W Molenkamp
- Physikalisches Institut (EP3), Universität Würzburg, 97074 Würzburg, Germany
| | - K Biermann
- Paul-Drude-Institut für Festkörperelektronik, 10117 Berlin, Germany
| | - P V Santos
- Paul-Drude-Institut für Festkörperelektronik, 10117 Berlin, Germany
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35
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Nowack KC, Spanton EM, Baenninger M, König M, Kirtley JR, Kalisky B, Ames C, Leubner P, Brüne C, Buhmann H, Molenkamp LW, Goldhaber-Gordon D, Moler KA. Imaging currents in HgTe quantum wells in the quantum spin Hall regime. Nat Mater 2013; 12:787-791. [PMID: 23770727 DOI: 10.1038/nmat3682] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2013] [Accepted: 05/07/2013] [Indexed: 06/02/2023]
Abstract
The quantum spin Hall (QSH) state is a state of matter characterized by a non-trivial topology of its band structure, and associated conducting edge channels. The QSH state was predicted and experimentally demonstrated to be realized in HgTe quantum wells. The existence of the edge channels has been inferred from local and non-local transport measurements in sufficiently small devices. Here we directly confirm the existence of the edge channels by imaging the magnetic fields produced by current flowing in large Hall bars made from HgTe quantum wells. These images distinguish between current that passes through each edge and the bulk. On tuning the bulk conductivity by gating or raising the temperature, we observe a regime in which the edge channels clearly coexist with the conducting bulk, providing input to the question of how ballistic transport may be limited in the edge channels. Our results represent a versatile method for characterization of new QSH materials systems.
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Affiliation(s)
- Katja C Nowack
- 1] Department of Applied Physics, Stanford University, Stanford, California 94305, USA [2] Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
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36
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Maier L, Oostinga JB, Knott D, Brüne C, Virtanen P, Tkachov G, Hankiewicz EM, Gould C, Buhmann H, Molenkamp LW. Induced superconductivity in the three-dimensional topological insulator HgTe. Phys Rev Lett 2012; 109:186806. [PMID: 23215314 DOI: 10.1103/physrevlett.109.186806] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2012] [Indexed: 06/01/2023]
Abstract
A strained and undoped HgTe layer is a three-dimensional topological insulator, in which electronic transport occurs dominantly through its surface states. In this Letter, we present transport measurements on HgTe-based Josephson junctions with Nb as a superconductor. Although the Nb-HgTe interfaces have a low transparency, we observe a strong zero-bias anomaly in the differential resistance measurements. This anomaly originates from proximity-induced superconductivity in the HgTe surface states. In the most transparent junction, we observe periodic oscillations of the differential resistance as a function of an applied magnetic field, which correspond to a Fraunhofer-like pattern. This unambiguously shows that a precursor of the Josephson effect occurs in the topological surface states of HgTe.
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Affiliation(s)
- Luis Maier
- Physikalisches Institut, EP3, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
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37
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Dengel RG, Frey A, Brunner K, Gould C, Molenkamp LW. Fabrication of magnetic artificial atoms. Nanotechnology 2012; 23:395301. [PMID: 22962261 DOI: 10.1088/0957-4484/23/39/395301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We have fabricated gated vertical quantum dots made from a II-VI semiconductor heterostructure containing a paramagnetic quantum well. The absence of a known Schottky gate metal compatible with ZnSe based material precludes the traditional method of using a self-aligning shadow evaporated gate. Instead, we make use of a multi-step electron beam lithography process to surround a pillar with an insulating dielectric and gate. This process allows for the processing of dots with diameters down to 250 nm. Preliminary transport data confirming the magnetic nature of the resulting artificial atom are presented.
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Affiliation(s)
- R-G Dengel
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
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38
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Naydenova T, Dürrenfeld P, Tavakoli K, Pégard N, Ebel L, Pappert K, Brunner K, Gould C, Molenkamp LW. Diffusion thermopower of (Ga,Mn)As/GaAs tunnel junctions. Phys Rev Lett 2011; 107:197201. [PMID: 22181638 DOI: 10.1103/physrevlett.107.197201] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2011] [Indexed: 05/31/2023]
Abstract
We report the observation of tunneling anisotropic magnetothermopower, a voltage response to a temperature difference across an interface between a normal and a magnetic semiconductor. The resulting voltage is related to the energy derivative of the density of states in the magnetic material, and thus has a strongly anisotropic response to the direction of magnetization in the material. The effect will have relevance to the operation of semiconductor spintronic devices, and may indeed already play a role in correctly interpreting the details of some earlier spin injection studies.
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Affiliation(s)
- Ts Naydenova
- Physikalisches Institut EP3, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
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39
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Hancock JN, van Mechelen JLM, Kuzmenko AB, van der Marel D, Brüne C, Novik EG, Astakhov GV, Buhmann H, Molenkamp LW. Surface state charge dynamics of a high-mobility three-dimensional topological insulator. Phys Rev Lett 2011; 107:136803. [PMID: 22026887 DOI: 10.1103/physrevlett.107.136803] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Revised: 07/14/2011] [Indexed: 05/31/2023]
Abstract
We present a magneto-optical study of the three-dimensional topological insulator, strained HgTe, using a technique which capitalizes on advantages of time-domain spectroscopy to amplify the signal from the surface states. This measurement delivers valuable and precise information regarding the surface-state dispersion within <1 meV of the Fermi level. The technique is highly suitable for the pursuit of the topological magnetoelectric effect and axion electrodynamics.
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Affiliation(s)
- Jason N Hancock
- Département de Physique de la Matière Condensée, Université de Genève, Switzerland
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40
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Brüne C, Liu CX, Novik EG, Hankiewicz EM, Buhmann H, Chen YL, Qi XL, Shen ZX, Zhang SC, Molenkamp LW. Quantum Hall effect from the topological surface states of strained bulk HgTe. Phys Rev Lett 2011; 106:126803. [PMID: 21517339 DOI: 10.1103/physrevlett.106.126803] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2011] [Revised: 02/18/2011] [Indexed: 05/30/2023]
Abstract
We report transport studies on a three-dimensional, 70-nm-thick HgTe layer, which is strained by epitaxial growth on a CdTe substrate. The strain induces a band gap in the otherwise semimetallic HgTe, which thus becomes a three-dimensional topological insulator. Contributions from residual bulk carriers to the transport properties of the gapped HgTe layer are negligible at mK temperatures. As a result, the sample exhibits a quantized Hall effect that results from the 2D single cone Dirac-like topological surface states.
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Affiliation(s)
- C Brüne
- Faculty for Physics and Astronomy and Röntgen Center for Complex Material Systems, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
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41
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Shuvaev AM, Astakhov GV, Pimenov A, Brüne C, Buhmann H, Molenkamp LW. Giant magneto-optical faraday effect in HgTe thin films in the terahertz spectral range. Phys Rev Lett 2011; 106:107404. [PMID: 21469835 DOI: 10.1103/physrevlett.106.107404] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2010] [Indexed: 05/30/2023]
Abstract
We report the observation of a giant Faraday effect, using terahertz (THz) spectroscopy on epitaxial HgTe thin films at room temperature. The effect is caused by the combination of the unique band structure and the very high electron mobility of HgTe. Our observations suggest that HgTe is a high-potential material for applications as optical isolator and modulator in the THz spectral range.
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Affiliation(s)
- A M Shuvaev
- Institute of Solid State Physics, Vienna University of Technology, 1040 Vienna, Austria
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42
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Tkachov G, Thienel C, Pinneker V, Büttner B, Brüne C, Buhmann H, Molenkamp LW, Hankiewicz EM. Backscattering of Dirac fermions in HgTe quantum wells with a finite gap. Phys Rev Lett 2011; 106:076802. [PMID: 21405530 DOI: 10.1103/physrevlett.106.076802] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2010] [Indexed: 05/30/2023]
Abstract
The density-dependent mobility of n-type HgTe quantum wells with inverted band ordering has been studied both experimentally and theoretically. While semiconductor heterostructures with a parabolic dispersion exhibit an increase in mobility with carrier density, high-quality HgTe quantum wells exhibit a distinct mobility maximum. We show that this mobility anomaly is due to backscattering of Dirac fermions from random fluctuations of the band gap (Dirac mass). Our findings open new avenues for the study of Dirac fermion transport with finite and random mass, which so far has been hard to access.
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Affiliation(s)
- G Tkachov
- Fakultät für Physik und Astronomie and Röntgen Center for Complex Material Systems, Universität Würzburg, Am Hubland, Germany
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43
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Muck T, Leufgen M, Lebib A, Borzenko T, Geurts J, Schmidt G, Molenkamp LW, Wagner V, Gomes HL. Electrical Characterization of Vacuum Deposited and Solution Processed DH4T Thin Film Transistors. ACTA ACUST UNITED AC 2011. [DOI: 10.1557/proc-771-l10.3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
AbstractWe present organic field-effect transistors with dihexylquaterthiophene (DH4T) as active material, a derivative of the oligothiophene á-4T with two hexyl chains as end groups. This substitution makes this molecule suitable not only for vacuum sublimation but also for solution processing which enables cheaper production. Additionally, the layer ordering is improved. We compare vacuum deposited and solution processed OFETs based on DH4T. The former ones show nearly ideal I-V characteristics. The latter ones show deviations from ideal behavior and lower currents. Furthermore, temperature dependent measurements of drain-source current in vacuum deposited DH4T-OFETs shows an unusual variation of the OFET apparent mobility. These apparent changes in mobility are caused by a threshold voltage shift, which becomes pronounced at around 290 K
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44
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Mark S, Dürrenfeld P, Pappert K, Ebel L, Brunner K, Gould C, Molenkamp LW. Fully electrical read-write device out of a ferromagnetic semiconductor. Phys Rev Lett 2011; 106:057204. [PMID: 21405428 DOI: 10.1103/physrevlett.106.057204] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2010] [Indexed: 05/30/2023]
Abstract
We report the realization of a read-write device out of the ferromagnetic semiconductor (Ga,Mn)As as the first step to a fundamentally new information processing paradigm. Writing the magnetic state is achieved by current-induced switching and readout of the state is done by the means of the tunneling anisotropic magnetoresistance effect. This 1 bit demonstrator device can be used to design an electrically programmable memory and logic device.
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Affiliation(s)
- S Mark
- Physikalisches Institut (EP3) and Röntgen Center for Complex Material Systems, Am Hubland, Universität Würzburg, D-97074 Würzburg, Germany
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45
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Astakhov GV, Schwittek J, Schott GM, Gould C, Ossau W, Brunner K, Molenkamp LW. Photoinduced Barkhausen effect in the ferromagnetic semiconductor (Ga,Mn)As. Phys Rev Lett 2011; 106:037204. [PMID: 21405292 DOI: 10.1103/physrevlett.106.037204] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2010] [Indexed: 05/30/2023]
Abstract
Magnetization of ferromagnetic materials commonly occurs via random jumps of domain walls between pinning sites, a phenomenon known as the Barkhausen effect. Using strongly focused light pulses of appropriate power and duration we demonstrate the ability to selectively activate single jumps in the domain wall propagation in (Ga,Mn)As, manifesting itself as a discrete photoinduced domain wall creep as a function of illumination time. The propagation velocity can be increased over 7 orders of magnitude varying the illumination power density and the magnetic field.
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Affiliation(s)
- G V Astakhov
- Physikalisches Institut, EP3, Universität Würzburg, 97074 Würzburg, Germany.
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46
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Pfattner R, Mas-Torrent M, Bilotti I, Brillante A, Milita S, Liscio F, Biscarini F, Marszalek T, Ulanski J, Nosal A, Gazicki-Lipman M, Leufgen M, Schmidt G, Molenkamp LW, Laukhin V, Veciana J, Rovira C. High-performance single crystal organic field-effect transistors based on two dithiophene-tetrathiafulvalene (DT-TTF) polymorphs. Adv Mater 2010; 22:4198-4203. [PMID: 20564710 DOI: 10.1002/adma.201001446] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Solution prepared single crystal organic field-effect transistors (OFETs) combine low-cost with high performance due to structural ordering of molecules. However, in organic crystals polymorphism is a known phenomenon, which can have a crucial influence on charge transport. Here, the performance of solution-prepared single crystal OFETs based on two different polymorphs of dithiophene-tetrathiafulvalene, which were investigated by confocal Raman spectroscopy and X-ray diffraction, are reported. OFET devices prepared using different configurations show that both polymorphs exhibited excellent device performance, although the -phase revealed charge carrier mobility between two and ten times higher in accordance to the closer stacking of the molecules.
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Affiliation(s)
- Raphael Pfattner
- Institut de Ciencia de Materials de Barcelona, Bellaterra, Spain
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47
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Mark S, Gould C, Pappert K, Wenisch J, Brunner K, Schmidt G, Molenkamp LW. Independent magnetization behavior of a ferromagnetic metal-semiconductor hybrid system. Phys Rev Lett 2009; 103:017204. [PMID: 19659175 DOI: 10.1103/physrevlett.103.017204] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2009] [Indexed: 05/28/2023]
Abstract
We report the discovery of an effect where two ferromagnetic materials, one semiconductor [(Ga,Mn)As] and one metal (Permalloy), can be directly deposited on each other and still switch their magnetization independently. We use this independent magnetization behavior to create various resistance states dependent on the magnetization direction of the individual layers. At zero magnetic field a two layer device can reach up to four nonvolatile resistance states.
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Affiliation(s)
- S Mark
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
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48
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Astakhov GV, Hoffmann H, Korenev VL, Kiessling T, Schwittek J, Schott GM, Gould C, Ossau W, Brunner K, Molenkamp LW. Nonthermal photocoercivity effect in a low-doped (Ga,Mn)As ferromagnetic semiconductor. Phys Rev Lett 2009; 102:187401. [PMID: 19518911 DOI: 10.1103/physrevlett.102.187401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2008] [Indexed: 05/27/2023]
Abstract
We report a photoinduced change of the coercive field, i.e., a photocoercivity effect (PCE), under very low intensity illumination of a low-doped (Ga,Mn)As ferromagnetic semiconductor. We find a strong correlation between the PCE and the sample resistivity. Spatially resolved dynamics of the magnetization reversal rule out any role of thermal heating in the origin of this PCE, and we propose a mechanism based on the light-induced lowering of the domain wall pinning energy. The PCE is local and reversible, allowing writing and erasing of magnetic images using light.
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Affiliation(s)
- G V Astakhov
- Physikalisches Institut (EP3), Universität Würzburg, 97074 Würzburg, Germany.
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49
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de Loubens G, Riegler A, Pigeau B, Lochner F, Boust F, Guslienko KY, Hurdequint H, Molenkamp LW, Schmidt G, Slavin AN, Tiberkevich VS, Vukadinovic N, Klein O. Bistability of vortex core dynamics in a single perpendicularly magnetized nanodisk. Phys Rev Lett 2009; 102:177602. [PMID: 19518834 DOI: 10.1103/physrevlett.102.177602] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2008] [Revised: 04/01/2009] [Indexed: 05/27/2023]
Abstract
Microwave spectroscopy of individual vortex-state magnetic nanodisks in a perpendicular bias magnetic field H is performed using a magnetic resonance force microscope. It reveals the splitting induced by H on the gyrotropic frequency of the vortex core rotation related to the existence of the two stable polarities of the core. This splitting enables spectroscopic detection of the core polarity. The bistability extends up to a large negative (antiparallel to the core) value of the bias magnetic field Hr, at which the core polarity is reversed. The difference between the frequencies of the two stable rotational modes corresponding to each core polarity is proportional to H and to the ratio of the disk thickness to its radius. Simple analytic theory in combination with micromagnetic simulations give a quantitative description of the observed bistable dynamics.
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Affiliation(s)
- G de Loubens
- Service de Physique de l'Etat Condensé (CNRS URA 2464), CEA Saclay, 91191 Gif-sur-Yvette, France.
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50
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Astakhov GV, Dzhioev RI, Kavokin KV, Korenev VL, Lazarev MV, Tkachuk MN, Kusrayev YG, Kiessling T, Ossau W, Molenkamp LW. Suppression of electron spin relaxation in Mn-doped GaAs. Phys Rev Lett 2008; 101:076602. [PMID: 18764562 DOI: 10.1103/physrevlett.101.076602] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2007] [Indexed: 05/26/2023]
Abstract
We report a surprisingly long spin relaxation time of electrons in Mn-doped p-GaAs. The spin relaxation time scales with the optical pumping and increases from 12 ns in the dark to 160 ns upon saturation. This behavior is associated with the difference in spin relaxation rates of electrons precessing in the fluctuating fields of ionized or neutral Mn acceptors, respectively. For the latter, the antiferromagnetic exchange interaction between a Mn ion and a bound hole results in a partial compensation of these fluctuating fields, leading to the enhanced spin memory.
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Affiliation(s)
- G V Astakhov
- Physikalisches Institut (EP3), Universität Würzburg, 97074 Würzburg, Germany.
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