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Stepanov VA, Lin C, Gonnelli RS, Tortello M. Probing the current-phase relation in Josephson point-contact junctions between [Formula: see text]In[Formula: see text] and [Formula: see text]K[Formula: see text](FeAs)[Formula: see text] superconductors. Sci Rep 2021; 11:23986. [PMID: 34907197 PMCID: PMC8671446 DOI: 10.1038/s41598-021-00762-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2021] [Accepted: 09/27/2021] [Indexed: 11/24/2022] Open
Abstract
The Josephson effect in point contacts between an "ordinary" superconductor [Formula: see text]In[Formula: see text] ([Formula: see text]) and single crystals of the Fe-based superconductor Ba[Formula: see text]K[Formula: see text](FeAs)[Formula: see text] ([Formula: see text]), was investigated. In order to shed light on the order parameter symmetry of Ba[Formula: see text]K[Formula: see text](FeAs)[Formula: see text], the dependence of the Josephson supercurrent [Formula: see text] on the temperature and on [Formula: see text] with [Formula: see text] was studied. The dependencies of the critical current on temperature [Formula: see text] and of the amplitudes of the first current steps of the current-voltage characteristic [Formula: see text] [Formula: see text] on the power of microwave radiation with frequency [Formula: see text] were measured. It is shown that the dependencies [Formula: see text] are close to the well-known Ambegaokar-Baratoff (AB) dependence for tunnel contacts between "ordinary" superconductors and to the dependence calculated by Burmistrova et al. (Phys Rev B 91, 214501 (2015)) for microshorts between an "ordinary" superconductor and a two-band superconductor with [Formula: see text] order parameter symmetry at certain values of the transparency of boundaries and thickness of the transition layer. It is found that the dependencies [Formula: see text] cannot be approximated within the resistively shunted model using the normalized microwave frequencies [Formula: see text] with characteristic voltages [Formula: see text], [Formula: see text]-normal resistance of the contact) found from the low-voltage parts of the current-voltage characteristics. The reasons for this failure are discussed and a method is proposed for accurately determining the value of [Formula: see text], which takes into account all the features of the point contact affecting the period of the dependence [Formula: see text]. An analysis of the [Formula: see text] and [Formula: see text] dependencies shows that the superconducting current of the Josephson contacts under investigation is proportional to the [Formula: see text] of the phase difference [Formula: see text], [Formula: see text]. The implications of these results on the symmetry of the order parameter are also discussed.
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Affiliation(s)
- Valeriy A. Stepanov
- P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow, Russia 119333
| | - Chengtian Lin
- Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart, Germany
| | - Renato S. Gonnelli
- Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, Torino, 10129 Italy
| | - Mauro Tortello
- Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, Torino, 10129 Italy
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2
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Zhu X. Second-Order Topological Superconductors with Mixed Pairing. PHYSICAL REVIEW LETTERS 2019; 122:236401. [PMID: 31298896 DOI: 10.1103/physrevlett.122.236401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Revised: 04/03/2019] [Indexed: 06/10/2023]
Abstract
We show that a two-dimensional semiconductor with Rashba spin-orbit coupling could be driven into the second-order topological superconducting phase when a mixed-pairing state is introduced. The superconducting order we consider involves only even-parity components and meanwhile breaks time-reversal symmetry. As a result, each corner of a square-shaped Rashba semiconductor would host one single Majorana zero mode in the second-order nontrivial phase. Starting from edge physics, we are able to determine the phase boundaries accurately. A simple criterion for the second-order phase is further established, which concerns the relative position between Fermi surfaces and nodal points of the superconducting order parameter. In the end, we propose two setups that may bring this mixed-pairing state into the Rashba semiconductor, followed by a brief discussion on the experimental feasibility of the two platforms.
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Affiliation(s)
- Xiaoyu Zhu
- School of Science, MOE Key Laboratory for Non-equilibrium Synthesis and Modulation of Condensed Matter, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China
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3
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Tortello M, Park WK, Ascencio CO, Saraf P, Greene LH. Design and construction of a point-contact spectroscopy rig with lateral scanning capability. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2016; 87:063903. [PMID: 27370466 DOI: 10.1063/1.4953340] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Accepted: 05/23/2016] [Indexed: 06/06/2023]
Abstract
The design and realization of a cryogenic rig for point-contact spectroscopy measurements in the needle-anvil configuration is presented. Thanks to the use of two piezoelectric nano-positioners, the tip can move along the vertical (z) and horizontal (x) direction and thus the rig is suitable to probe different regions of a sample in situ. Moreover, it can also form double point-contacts on different facets of a single crystal for achieving, e.g., an interferometer configuration for phase-sensitive measurements. For the later purpose, the sample holder can also host a Helmholtz coil for applying a small transverse magnetic field to the junction. A semi-rigid coaxial cable can be easily added for studying the behavior of Josephson junctions under microwave irradiation. The rig can be detached from the probe and thus used with different cryostats. The performance of this new probe has been tested in a Quantum Design PPMS system by conducting point-contact Andreev reflection measurements on Nb thin films over large areas as a function of temperature and magnetic field.
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Affiliation(s)
- M Tortello
- Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, Torino 10129, Italy
| | - W K Park
- Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - C O Ascencio
- Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - P Saraf
- Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - L H Greene
- Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
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4
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Ultrafast dynamics of quasiparticles and coherent acoustic phonons in slightly underdoped (BaK)Fe2As2. Sci Rep 2016; 6:25962. [PMID: 27180873 PMCID: PMC4867611 DOI: 10.1038/srep25962] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Accepted: 04/26/2016] [Indexed: 11/13/2022] Open
Abstract
We have utilized ultrafast optical spectroscopy to study carrier dynamics in slightly underdoped (BaK)Fe2As2 crystals without magnetic transition. The photoelastic signals due to coherent acoustic phonons have been quantitatively investigated. According to our temperature-dependent results, we found that the relaxation component of superconducting quasiparticles persisted from the superconducting state up to at least 70 K in the normal state. Our findings suggest that the pseudogaplike feature in the normal state is possibly the precursor of superconductivity. We also highlight that the pseudogap feature of K-doped BaFe2As2 is different from that of other iron-based superconductors, including Co-doped or P-doped BaFe2As2.
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5
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Concealed d-wave pairs in the s± condensate of iron-based superconductors. Proc Natl Acad Sci U S A 2016; 113:5486-91. [PMID: 27140626 DOI: 10.1073/pnas.1523064113] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A central question in iron-based superconductivity is the mechanism by which the paired electrons minimize their strong mutual Coulomb repulsion. In most unconventional superconductors, Coulomb repulsion is minimized through the formation of higher angular momentum Cooper pairs, with Fermi surface nodes in the pair wavefunction. The apparent absence of such nodes in the iron-based superconductors has led to a belief they form an s-wave ([Formula: see text]) singlet state, which changes sign between the electron and hole pockets. However, the multiorbital nature of these systems opens an alternative possibility. Here, we propose a new class of [Formula: see text] state containing a condensate of d-wave Cooper pairs, concealed by their entanglement with the iron orbitals. By combining the d-wave ([Formula: see text]) motion of the pairs with the internal angular momenta [Formula: see text] of the iron orbitals to make a singlet ([Formula: see text]), an [Formula: see text] superconductor with a nontrivial topology is formed. This scenario allows us to understand the development of octet nodes in potassium-doped Ba1-x KXFe2As2 as a reconfiguration of the orbital and internal angular momentum into a high spin ([Formula: see text]) state; the reverse transition under pressure into a fully gapped state can then be interpreted as a return to the low-spin singlet. The formation of orbitally entangled pairs is predicted to give rise to a shift in the orbital content at the Fermi surface, which can be tested via laser-based angle-resolved photoemission spectroscopy.
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Ong TT, Coleman P. Tetrahedral and orbital pairing: a fully gapped pairing scenario for the iron-based superconductors. PHYSICAL REVIEW LETTERS 2013; 111:217003. [PMID: 24313519 DOI: 10.1103/physrevlett.111.217003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2013] [Indexed: 06/02/2023]
Abstract
Motivated by the fully gapped superconductivity in iron-based superconductors with uncompensated electron pockets, we propose a spin singlet, but orbital triplet analogue of the superfluid phase of ^{3}He-B. We show that orbital triplets with a nominal d-wave symmetry at the iron sites can transform as s-wave pairs under rotations about the selenium sites. Linear combinations of such d(xy) and d(x2-y(2)) triplets form a fully gapped, topological superconductor. Raman-active excitations are predicted to develop below the superconducting transition temperature.
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Affiliation(s)
- T Tzen Ong
- Center for Materials Theory, Department of Physics & Astronomy, Rutgers University, Piscataway New Jersey 08854, USA
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Song CL, Wang YL, Cheng P, Jiang YP, Li W, Zhang T, Li Z, He K, Wang L, Jia JF, Hung HH, Wu C, Ma X, Chen X, Xue QK. Direct Observation of Nodes and Twofold Symmetry in FeSe Superconductor. Science 2011; 332:1410-3. [DOI: 10.1126/science.1202226] [Citation(s) in RCA: 333] [Impact Index Per Article: 25.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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8
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Abstract
The past three years have witnessed the discovery of a series of novel high-temperature superconductors. Trailing behind the cuprates, these iron-based compounds are the second-highest-temperature superconducting material family known to date. Despite the marked differences in the chemical composition, these materials share many properties with the cuprates and offer the hope of finally unveiling the secret of high-temperature superconductivity. The main theme of this review is the electron-pairing mechanism responsible for their superconductivity. We discuss the progress in this young field and point out the open issues.
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Affiliation(s)
- Fa Wang
- Department of Physics, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA
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9
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Berg E, Lindner NH, Pereg-Barnea T. Metastable π junction between an s(±)-wave and an s-wave superconductor. PHYSICAL REVIEW LETTERS 2011; 106:147003. [PMID: 21561215 DOI: 10.1103/physrevlett.106.147003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2011] [Indexed: 05/30/2023]
Abstract
We examine a contact between a superconductor whose order parameter changes sign across the Brillioun zone, and an ordinary, uniform-sign superconductor. Within a Ginzburg-Landau-type model, we find that if the barrier between the two superconductors is not too high, the frustration of the Josephson coupling between different portions of the Fermi surface across the contact can lead to surprising consequences. These include time-reversal symmetry breaking at the interface and unusual energy-phase relations with multiple local minima. We propose this mechanism as a possible explanation for the half-integer flux quantum transitions in composite niobium-iron pnictide superconducting loops, which were discovered in recent experiments [C.-T. Chen et al., Nature Phys. 6, 260 (2010).].
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Affiliation(s)
- E Berg
- Physics Department, Harvard University, Cambridge, Massachusetts 02138, USA
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10
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Zeng B, Mu G, Luo H, Xiang T, Mazin I, Yang H, Shan L, Ren C, Dai P, Wen HH. Anisotropic structure of the order parameter in FeSe(0.45)Te(0.55) revealed by angle-resolved specific heat. Nat Commun 2010; 1:112. [PMID: 21081910 PMCID: PMC3066551 DOI: 10.1038/ncomms1115] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2010] [Accepted: 10/18/2010] [Indexed: 11/09/2022] Open
Abstract
The central issues for understanding iron (Fe)-based superconductors are the symmetry and structure of the superconducting gap. So far the experimental data and theoretical models have been highly controversial. Some experiments favor two or more constant or nearly constant gaps, others indicate strong anisotropy and yet others suggest gap zeros ('nodes'). A unique method for addressing this issue, and one of very few methods that are bulk and angle resolved, is measuring the electronic-specific heat in a rotating magnetic field. In this study, we present the first such measurement for an Fe-based high-T(c) superconductor. We observed a fourfold oscillation of the specific heat as a function of the in-plane magnetic field direction. Our results are consistent with the expectations for an extended s-wave model, with a significant gap anisotropy on the electron pockets and the gap minima along the ΓM (Fe-Fe bond) direction.
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Affiliation(s)
- B. Zeng
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - G. Mu
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - H.Q. Luo
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - T. Xiang
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - I.I. Mazin
- Code 6391, Naval Research Laboratory, Washington, District of Columbia 20375, USA
| | - H. Yang
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
- National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
| | - L. Shan
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - C. Ren
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - P.C. Dai
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
- Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996-1200, USA
- Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6393, USA
| | - H.-H. Wen
- National Laboratory for Superconductivity, Institute of Physics and National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
- National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
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11
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Chen WQ, Ma F, Lu ZY, Zhang FC. Pi junction to probe antiphase s-wave pairing in iron pnictide superconductors. PHYSICAL REVIEW LETTERS 2009; 103:207001. [PMID: 20366003 DOI: 10.1103/physrevlett.103.207001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2009] [Indexed: 05/29/2023]
Abstract
Josephson junctions between a FeAs-based superconductor with antiphase s-wave pairing and a conventional s-wave superconductor are studied. The translational invariance in a planar junction between a single crystal pnictide and an aluminum metal greatly enhances the relative weight of electron pockets in the pnictide to the critical current. In a wide doping region of the pnictide, a planar and a point contact junction have opposite phases, which can be used to design a trijunction ring with pi phase to probe the antiphase pairing.
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Affiliation(s)
- Wei-Qiang Chen
- Department of Physics, and Center of Theoretical and Computational Physics, the University of Hong Kong, Hong Kong, China
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12
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Parker D, Mazin II. Possible phase-sensitive tests of pairing symmetry in pnictide superconductors. PHYSICAL REVIEW LETTERS 2009; 102:227007. [PMID: 19658896 DOI: 10.1103/physrevlett.102.227007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2008] [Indexed: 05/28/2023]
Abstract
The discovery of the new class of pnictide superconductors has engendered a controversy about their pairing symmetry, with proposals ranging from an extended s wave or "s_{+/-}" symmetry to nodal or nodeless d-wave symmetry to still more exotic order parameters such as p wave. In this Letter, building on the earlier, similar work performed for the cuprates, we propose several phase-sensitive Josephson interferometry experiments, each of which may allow resolution of the issue.
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Affiliation(s)
- D Parker
- Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, D.C., 20375, USA
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