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Zakeri K, Rau D, Jandke J, Yang F, Wulfhekel W, Berthod C. Direct Probing of a Large Spin-Orbit Coupling in the FeSe Superconducting Monolayer on STO. ACS NANO 2023; 17:9575-9585. [PMID: 37155694 DOI: 10.1021/acsnano.3c02876] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Spin-orbit coupling (SOC) is a fundamental physical interaction, which describes how the electrons' spin couples to their orbital motion. It is the source of a vast variety of fascinating phenomena in nanostructures. Although in most theoretical descriptions of high-temperature superconductivity SOC has been neglected, including this interaction can, in principle, revise the microscopic picture. Here by preforming energy-, momentum-, and spin-resolved spectroscopy experiments we demonstrate that while probing the dynamic charge response of the FeSe monolayer on strontium titanate, a prototype two-dimensional high-temperature superconductor using electrons, the scattering cross-section is spin dependent. We unravel the origin of the observed phenomenon and show that SOC in this two-dimensional superconductor is strong. We anticipate that such a strong SOC can have several consequences on the electronic structures and may compete with other pairing scenarios and be crucial for the mechanism of superconductivity.
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Affiliation(s)
- Khalil Zakeri
- Heisenberg Spin-dynamics Group, Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Straße 1, D-76131 Karlsruhe, Germany
| | - Dominik Rau
- Heisenberg Spin-dynamics Group, Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Straße 1, D-76131 Karlsruhe, Germany
| | - Jasmin Jandke
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Straße 1, D-76131 Karlsruhe, Germany
| | - Fang Yang
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Straße 1, D-76131 Karlsruhe, Germany
| | - Wulf Wulfhekel
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Straße 1, D-76131 Karlsruhe, Germany
- Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology, D-76344, Eggenstein-Leopoldshafen, Germany
| | - Christophe Berthod
- Department of Quantum Matter Physics, University of Geneva, 1211 Geneva, Switzerland
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Chen J, Gamża MB, Banda J, Murphy K, Tarrant J, Brando M, Grosche FM. Unconventional Bulk Superconductivity in YFe_{2}Ge_{2} Single Crystals. PHYSICAL REVIEW LETTERS 2020; 125:237002. [PMID: 33337220 DOI: 10.1103/physrevlett.125.237002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Revised: 09/17/2020] [Accepted: 10/09/2020] [Indexed: 06/12/2023]
Abstract
Sharp superconducting transition anomalies observed in a new generation of single crystals establish that bulk superconductivity is intrinsic to high purity YFe_{2}Ge_{2}. Low temperature heat capacity measurements suggest a disorder and field dependent residual Sommerfeld coefficient, consistent with disorder-induced in-gap states as expected for a sign-changing order parameter. The sevenfold reduction in disorder scattering in these new crystals to residual resistivities ≃0.45 μΩ cm was achieved using a new liquid transport growth technique, paving the way for multiprobe experiments investigating the normal and superconducting states of YFe_{2}Ge_{2}.
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Affiliation(s)
- Jiasheng Chen
- Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
| | - Monika B Gamża
- Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, University of Central Lancashire, PR1 2HE Preston, United Kingdom
| | - Jacintha Banda
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
| | - Keiron Murphy
- Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
| | - James Tarrant
- Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
| | - Manuel Brando
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
| | - F Malte Grosche
- Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
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Lopes N, Barci DG, Continentino MA. Finite temperature effects in quantum systems with competing scalar orders. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:415601. [PMID: 32512551 DOI: 10.1088/1361-648x/ab9a7c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2020] [Accepted: 06/08/2020] [Indexed: 06/11/2023]
Abstract
The study of the competition or coexistence of different ground states in many-body systems is an exciting and actual topic of research, both experimentally and theoretically. Quantum fluctuations of a given phase can suppress or enhance another phase depending on the nature of the coupling between the order parameters, their dynamics and the dimensionality of the system. The zero temperature phase diagrams of systems with competing scalar order parameters with quartic and bilinear coupling terms have been previously studied for the cases of a zero temperature bicritical point and of coexisting orders. In this work, we apply theMatsubara summationtechnique from finite temperature quantum field theory to introduce the effects of thermal fluctuations on the effective potential of these systems. This is essential to make contact with experiments. We consider two and three-dimensional materials characterized by a Lorentz invariant quantum critical theory, i.e., with dynamic critical exponentz= 1, such that time and space scale in the same way. We obtain that in both cases, thermal fluctuations lead to weak first-order temperature phase transitions, at which coexisting phases arising from quantum corrections become unstable. We show that above this critical temperature (Tc), the system presents scaling behavior consistent with that approaching a quantum critical point. Below the transition the specific heat has a thermally activated contribution with a gap related to the size of the domains of the ordered phases. We obtain thatTcdecreases as a function of the distance to the zero temperature classical bicritical point (ZTCBP) in the coexistence region, implying that in our approach, the system attains the highestTcabove the fine tuned value of this ZTCBP.
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Affiliation(s)
- Nei Lopes
- Centro Brasileiro de Pesquisas Físicas, Rua Dr Xavier Sigaud 150, Urca, 22290-180, Rio de Janeiro, Brazil
| | - Daniel G Barci
- Departamento de Física Teórica, Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524, 20550-013, Rio de Janeiro, RJ, Brazil
| | - Mucio A Continentino
- Centro Brasileiro de Pesquisas Físicas, Rua Dr Xavier Sigaud 150, Urca, 22290-180, Rio de Janeiro, Brazil
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Hong J. Analyzing scanning tunneling spectroscopy for Fe-based superconductors and extracting sample density of states. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:375602. [PMID: 31163407 DOI: 10.1088/1361-648x/ab26fb] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We extract the density of states (DOS) from the scanning tunneling spectroscopy data for Ba1-x K x Fe2As2 superconductor. The obtained sample DOS is composed of two ordinary s-wave types from the band at [Formula: see text] point and a linear-like DOS within the s-wave gap from the band at M point in the Brillouin zone, and is consistent with the corresponding data from angle-resolved photoemission spectroscopy. We clarify that the major peak of the tunneling conductance is not related to the DOS but is rather the effect of nonequilibrium coherent tunneling including all coherent spins in the tip and sample.
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Affiliation(s)
- Jongbae Hong
- Research Institute of Basic Sciences, Incheon National University, Yeonsu-gu, Incheon 22012, Republic of Korea
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5
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Classifying Induced Superconductivity in Atomically Thin Dirac-Cone Materials. CONDENSED MATTER 2019. [DOI: 10.3390/condmat4030083] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Recently, Kayyalha et al. (Phys. Rev. Lett., 2019, 122, 047003) reported on the anomalous enhancement of the self-field critical currents (Ic (sf, T)) at low temperatures in Nb/BiSbTeSe2-nanoribbon/Nb Josephson junctions. The enhancement was attributed to the low-energy Andreev-bound states arising from the winding of the electronic wave function around the circumference of the topological insulator BiSbTeSe2 nanoribbon. It should be noted that identical enhancement in Ic (sf, T) and in the upper critical field (Bc2 (T)) in approximately the same reduced temperatures, were reported by several research groups in atomically thin junctions based on a variety of Dirac-cone materials (DCM) earlier. The analysis shows that in all these S/DCM/S systems, the enhancement is due to a new superconducting band opening. Taking into account that several intrinsic superconductors also exhibit the effect of new superconducting band(s) opening when sample thickness becomes thinner than the out-of-plane coherence length (c (0)), we reaffirm our previous proposal that there is a new phenomenon of additional superconducting band(s) opening in atomically thin films.
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Costanzo D, Zhang H, Reddy BA, Berger H, Morpurgo AF. Tunnelling spectroscopy of gate-induced superconductivity in MoS 2. NATURE NANOTECHNOLOGY 2018; 13:483-488. [PMID: 29713077 DOI: 10.1038/s41565-018-0122-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2017] [Accepted: 03/23/2018] [Indexed: 06/08/2023]
Abstract
The ability to gate-induce superconductivity by electrostatic charge accumulation is a recent breakthrough in physics and nanoelectronics. With the exception of LaAlO3/SrTiO3 interfaces, experiments on gate-induced superconductors have been largely confined to resistance measurements, which provide very limited information about the superconducting state. Here, we explore gate-induced superconductivity in MoS2 by performing tunnelling spectroscopy to determine the energy-dependent density of states (DOS) for different levels of electron density n. In the superconducting state, the DOS is strongly suppressed at energy smaller than the gap Δ, which is maximum (Δ ~2 meV) for n of ~1 × 1014 cm-2 and decreases monotonously for larger n. A perpendicular magnetic field B generates states at E < Δ that fill the gap, but a 20% DOS suppression of superconducting origin unexpectedly persists much above the transport critical field. Conversely, an in-plane field up to 10 T leaves the DOS entirely unchanged. Our measurements exclude that the superconducting state in MoS2 is fully gapped and reveal the presence of a DOS that vanishes linearly with energy, the explanation of which requires going beyond a conventional, purely phonon-driven Bardeen-Cooper-Schrieffer mechanism.
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Affiliation(s)
| | - Haijing Zhang
- DQMP and GAP, Université de Genève, Geneva, Switzerland
| | | | - Helmuth Berger
- Institut de Physique de la Matière Complexe, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland
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Li Y, Liu M, Fu Z, Chen X, Yang F, Yang YF. Gap Symmetry of the Heavy Fermion Superconductor CeCu_{2}Si_{2} at Ambient Pressure. PHYSICAL REVIEW LETTERS 2018; 120:217001. [PMID: 29883182 DOI: 10.1103/physrevlett.120.217001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/05/2018] [Indexed: 06/08/2023]
Abstract
Recent observations of two nodeless gaps in superconducting CeCu_{2}Si_{2} have raised intensive debates on its exact gap symmetry, while a satisfactory theoretical basis is still lacking. Here we propose a phenomenological approach to calculate the superconducting gap functions, taking into consideration both the realistic Fermi surface topology and the intra- and interband quantum critical scatterings. Our calculations yield a nodeless s^{±}-wave solution in the presence of strong interband pairing interaction, in good agreement with experiments. This provides a possible basis for understanding the superconducting gap symmetry of CeCu_{2}Si_{2} at ambient pressure and indicates the potential importance of multiple Fermi surfaces and interband pairing interaction in understanding heavy fermion superconductivity.
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Affiliation(s)
- Yu Li
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Min Liu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- College of Physical Science and Technology, Sichuan University, Chengdu 610065, China
| | - Zhaoming Fu
- College of Physics and Material Science, Henan Normal University, Xinxiang 453007, China
| | - Xiangrong Chen
- College of Physical Science and Technology, Sichuan University, Chengdu 610065, China
| | - Fan Yang
- School of Physics, Beijing Institute of Technology, Beijing 100081, China
| | - Yi-Feng Yang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100190, China
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Ghigo G, Ummarino GA, Gozzelino L, Gerbaldo R, Laviano F, Torsello D, Tamegai T. Effects of disorder induced by heavy-ion irradiation on (Ba 1-x K x )Fe 2As 2 single crystals, within the three-band Eliashberg s± wave model. Sci Rep 2017; 7:13029. [PMID: 29026182 PMCID: PMC5638861 DOI: 10.1038/s41598-017-13303-5] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2017] [Accepted: 09/22/2017] [Indexed: 11/09/2022] Open
Abstract
One of the open issues concerning iron-based superconductors is whether the s± wave model is able to account for the overall effects of impurity scattering, including the low rate of decrease of the critical temperature with the impurity concentration. Here we investigate Ba1-x K x Fe2As2 crystals where disorder is introduced by Au-ion irradiation. Critical temperature, T c , and London penetration depth, λ L , were measured by a microwave resonator technique, for different values of the irradiation fluence. We compared experimental data with calculations made on the basis of the three-band Eliashberg equations, suitably accounting for the impurity scattering. We show that this approach is able to explain in a consistent way the effects of disorder both on T c and on λ L (T), within the s± wave model. In particular, a change of curvature in the low-temperature λ L (T) curves for the most irradiated crystals is fairly well reproduced.
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Affiliation(s)
- G Ghigo
- Politecnico di Torino, Department of Applied Science and Technology, Torino, 10129, Italy. .,Istituto Nazionale di Fisica Nucleare, Sez. Torino, Torino, 10125, Italy.
| | - G A Ummarino
- Politecnico di Torino, Department of Applied Science and Technology, Torino, 10129, Italy.,National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moskva, 115409, Russia
| | - L Gozzelino
- Politecnico di Torino, Department of Applied Science and Technology, Torino, 10129, Italy.,Istituto Nazionale di Fisica Nucleare, Sez. Torino, Torino, 10125, Italy
| | - R Gerbaldo
- Politecnico di Torino, Department of Applied Science and Technology, Torino, 10129, Italy.,Istituto Nazionale di Fisica Nucleare, Sez. Torino, Torino, 10125, Italy
| | - F Laviano
- Politecnico di Torino, Department of Applied Science and Technology, Torino, 10129, Italy.,Istituto Nazionale di Fisica Nucleare, Sez. Torino, Torino, 10125, Italy
| | - D Torsello
- Politecnico di Torino, Department of Applied Science and Technology, Torino, 10129, Italy.,Istituto Nazionale di Fisica Nucleare, Sez. Torino, Torino, 10125, Italy
| | - T Tamegai
- The University of Tokyo, Department of Applied Physics, Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
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