1
|
Kölzer J, Rosenbach D, Weyrich C, Schmitt TW, Schleenvoigt M, Jalil AR, Schüffelgen P, Mussler G, Sacksteder Iv VE, Grützmacher D, Lüth H, Schäpers T. Phase-coherent loops in selectively-grown topological insulator nanoribbons. Nanotechnology 2020; 31:325001. [PMID: 32294631 DOI: 10.1088/1361-6528/ab898a] [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: 06/11/2023]
Abstract
We succeeded in the fabrication of topological insulator (Bi0.57Sb0.43)2Te3 Hall bars as well as nanoribbons by means of selective-area growth using molecular beam epitaxy. By performing magnetotransport measurements at low temperatures information on the phase-coherence of the electrons is gained by analyzing the weak-antilocalization effect. Furthermore, from measurements on nanoribbons at different magnetic field tilt angles an angular dependence of the phase-coherence length is extracted, which is attributed to transport anisotropy and geometrical factors. For the nanoribbon structures universal conductance fluctuations were observed. By performing a Fourier transform of the fluctuation pattern a series of distinct phase-coherent closed-loop trajectories are identified. The corresponding enclosed areas can be explained in terms of nanoribbon dimensions and phase-coherence length. In addition, from measurements at different magnetic field tilt angles we can deduce that the area enclosed by the loops are predominately oriented parallel to the quintuple layers.
Collapse
Affiliation(s)
- Jonas Kölzer
- Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich, Germany. JARA-Fundamentals of Future Information Technology, Jülich-Aachen Research Alliance, Forschungszentrum Jülich and RWTH Aachen University, Germany
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
2
|
Weyrich C, Lanius M, Schüffelgen P, Rosenbach D, Mussler G, Bunte S, Trellenkamp S, Grützmacher D, Schäpers T. Phase-coherent transport in selectively grown topological insulator nanodots. Nanotechnology 2019; 30:055201. [PMID: 30499462 DOI: 10.1088/1361-6528/aaee5f] [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: 06/09/2023]
Abstract
Oxidized Si(111) substrates were pre-structured by electron beam lithography and used as a substrate for the selective growth of three-dimensional topological insulators (TI) by molecular beam epitaxy. The patterned holes were filled up by the TI, i.e. Sb2Te3 and Bi2Te3, to form nanodots. Scanning electron microscopy and focused ion beam cross-sectioning was utilized to determine the morphology and depth profile of the nanodots. The magnetotransport measurements revealed universal conductance fluctuations originating from electron interference in phase-coherent loops. We find that these loops are oriented preferentially within the quintuple layers of the TI with only a small perpendicular contribution. Furthermore, we found clear indications of an conductivity anisotropy between different crystal orientations.
Collapse
Affiliation(s)
- Christian Weyrich
- Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, D-52425 Jülich, Germany. JARA-Fundamentals of Future Information Technology, Jülich-Aachen Research Alliance, Germany
| | | | | | | | | | | | | | | | | |
Collapse
|
3
|
Mooshammer F, Sandner F, Huber MA, Zizlsperger M, Weigand H, Plankl M, Weyrich C, Lanius M, Kampmeier J, Mussler G, Grützmacher D, Boland JL, Cocker TL, Huber R. Nanoscale Near-Field Tomography of Surface States on (Bi 0.5Sb 0.5) 2Te 3. Nano Lett 2018; 18:7515-7523. [PMID: 30419748 DOI: 10.1021/acs.nanolett.8b03008] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Three-dimensional topological insulators (TIs) have attracted tremendous interest for their possibility to host massless Dirac Fermions in topologically protected surface states (TSSs), which may enable new kinds of high-speed electronics. However, recent reports have outlined the importance of band bending effects within these materials, which results in an additional two-dimensional electron gas (2DEG) with finite mass at the surface. TI surfaces are also known to be highly inhomogeneous on the nanoscale, which is masked in conventional far-field studies. Here, we use near-field microscopy in the mid-infrared spectral range to probe the local surface properties of custom-tailored (Bi0.5Sb0.5)2Te3 structures with nanometer precision in all three spatial dimensions. Applying nanotomography and nanospectroscopy, we reveal a few-nanometer-thick layer of high surface conductivity and retrieve its local dielectric function without assuming any model for the spectral response. This allows us to directly distinguish between different types of surface states. An intersubband transition within the massive 2DEG formed by quantum confinement in the bent conduction band manifests itself as a sharp, surface-bound, Lorentzian-shaped resonance. An additional broadband background in the imaginary part of the dielectric function may be caused by the TSS. Tracing the intersubband resonance with nanometer spatial precision, we observe changes of its frequency, likely originating from local variations of doping or/and the mixing ratio between Bi and Sb. Our results highlight the importance of studying the surfaces of these novel materials on the nanoscale to directly access the local optical and electronic properties via the dielectric function.
Collapse
Affiliation(s)
- Fabian Mooshammer
- Department of Physics , University of Regensburg , 93040 Regensburg , Germany
| | - Fabian Sandner
- Department of Physics , University of Regensburg , 93040 Regensburg , Germany
| | - Markus A Huber
- Department of Physics , University of Regensburg , 93040 Regensburg , Germany
| | - Martin Zizlsperger
- Department of Physics , University of Regensburg , 93040 Regensburg , Germany
| | - Helena Weigand
- Department of Physics , University of Regensburg , 93040 Regensburg , Germany
| | - Markus Plankl
- Department of Physics , University of Regensburg , 93040 Regensburg , Germany
| | - Christian Weyrich
- Peter Grünberg Institut 9 , Forschungszentrum Jülich & JARA Jülich-Aachen Research Alliance , 52425 Jülich , Germany
| | - Martin Lanius
- Peter Grünberg Institut 9 , Forschungszentrum Jülich & JARA Jülich-Aachen Research Alliance , 52425 Jülich , Germany
| | - Jörn Kampmeier
- Peter Grünberg Institut 9 , Forschungszentrum Jülich & JARA Jülich-Aachen Research Alliance , 52425 Jülich , Germany
| | - Gregor Mussler
- Peter Grünberg Institut 9 , Forschungszentrum Jülich & JARA Jülich-Aachen Research Alliance , 52425 Jülich , Germany
| | - Detlev Grützmacher
- Peter Grünberg Institut 9 , Forschungszentrum Jülich & JARA Jülich-Aachen Research Alliance , 52425 Jülich , Germany
| | - Jessica L Boland
- Department of Physics , University of Regensburg , 93040 Regensburg , Germany
| | - Tyler L Cocker
- Department of Physics and Astronomy , Michigan State University , East Lansing , Michigan 48824 , United States
| | - Rupert Huber
- Department of Physics , University of Regensburg , 93040 Regensburg , Germany
| |
Collapse
|
4
|
Weyrich C, Drögeler M, Kampmeier J, Eschbach M, Mussler G, Merzenich T, Stoica T, Batov IE, Schubert J, Plucinski L, Beschoten B, Schneider CM, Stampfer C, Grützmacher D, Schäpers T. Growth, characterization, and transport properties of ternary (Bi 1-x Sb x ) 2Te 3 topological insulator layers. J Phys Condens Matter 2016; 28:495501. [PMID: 27749271 DOI: 10.1088/0953-8984/28/49/495501] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Ternary (Bi1-x Sb x )2Te3 films with an Sb content between 0 and 100% were deposited on a Si(1 1 1) substrate by means of molecular beam epitaxy. X-ray diffraction measurements confirm single crystal growth in all cases. The Sb content is determined by x-ray photoelectron spectroscopy. Consistent values of the Sb content are obtained from Raman spectroscopy. Scanning Raman spectroscopy reveals that the (Bi1-x Sb x )2Te3 layers with an intermediate Sb content show spatial composition inhomogeneities. The observed spectra broadening in angular-resolved photoemission spectroscopy (ARPES) is also attributed to this phenomena. Upon increasing the Sb content from x = 0 to 1 the ARPES measurements show a shift of the Fermi level from the conduction band to the valence band. This shift is also confirmed by corresponding magnetotransport measurements where the conductance changes from n- to p-type. In this transition region, an increase of the resistivity is found, indicating a location of the Fermi level within the band gap region. More detailed measurements in the transition region reveals that the transport takes place in two independent channels. By means of a gate electrode the transport can be changed from n- to p-type, thus allowing a tuning of the Fermi level within the topologically protected surface states.
Collapse
Affiliation(s)
- C Weyrich
- Peter Grünberg Institute (PGI-9) and JARA-Fundamentals of Future Information Technology, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany. Helmholtz Virtual Institute for Topological Insulators (VITI), Forschungszentrum Jülich, 52425 Jülich, Germany
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
5
|
Krimmel EE, Lutsch AG, Hoffman L, Weyrich C. SELFALIGNED METALLIC CONTACTS ON GaP : N-LEDs PROCESSED BY LASER PULSE IRRADIATION-INDUCED ABLATION. ACTA ACUST UNITED AC 1983. [DOI: 10.1051/jphyscol:1983568] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
|