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Swain D, Dey Sarkar M, Ptok A, Vaitheeswaran G, Roy A, D Das S. Evidences for local non-centrosymmetricity and strong phonon anomaly in EuCu 2As 2: a Raman spectroscopy and lattice dynamics study. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:335902. [PMID: 38670150 DOI: 10.1088/1361-648x/ad4441] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2024] [Accepted: 04/26/2024] [Indexed: 04/28/2024]
Abstract
Phonon modes and their association with the electronic states have been investigated for the metallic EuCu2As2system. In this work, we present the Raman spectra of this pnictide system which clearly shows the presence of seven well defined peaks above 100 cm-1that is consistent with the locally non-centrosymmetricP4/nmmcrystal structure, contrary to that what is expected from the accepted symmorphicI4/mmmstructure. Lattice dynamics calculations using theP4/nmmsymmetry attest that there is a commendable agreement between the calculated phonon spectra at the Γ point and the observed Raman mode frequencies, with the most intense peak at∼232 cm-1being ascribed to the A1gmode. Temperature dependent Raman measurements show that there is a significant deviation from the expected anharmonic behaviour around 165 K for the A1gmode, with anomalies being observed for several other modes as well, although to a lesser extent. Attempts are made to rationalize the observed anomalous behavior related to the hardening of the phonon modes, with parallels being drawn from metal dichalcogenide and allied systems. Similarities in the evolution of the Raman peak frequencies with temperature seem to suggest a strong signature of a subtle electronic density wave instability below 165 K in this compound.
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Affiliation(s)
- Debasmita Swain
- Department of Physics, Indian Institute of Technology Kharagpur, Kharagpur 721302, India
| | - Mainak Dey Sarkar
- School of Physics, University of Hyderabad, Gachibowli, Hyderabad 500046 Telangana, India
| | - Andrzej Ptok
- Institute of Nuclear Physics, Polish Academy of Sciences, W. E. Radzikowskiego 152, PL-31342 Kraków, Poland
| | - G Vaitheeswaran
- School of Physics, University of Hyderabad, Gachibowli, Hyderabad 500046 Telangana, India
| | - Anushree Roy
- Department of Physics, Indian Institute of Technology Kharagpur, Kharagpur 721302, India
| | - Sitikantha D Das
- Department of Physics, Indian Institute of Technology Kharagpur, Kharagpur 721302, India
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Karmakar M. Magnetotransport and Fermi surface segmentation in Pauli limited superconductors. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:165601. [PMID: 38190740 DOI: 10.1088/1361-648x/ad1bf6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2023] [Accepted: 01/08/2024] [Indexed: 01/10/2024]
Abstract
We report the first theoretical investigation of the spectroscopic, electrical and optical transport signatures ofd-wave Pauli limited superconductors, based on a non perturbative numerical approach. We demonstrate that the high magnetic field low temperature regime of these materials host a finite momentum paired superconducting phase. Multi-branched dispersion spectra with finite energy superconducting gaps, anisotropic segmentation of the Fermi surface and spatial modulations of the superconducting order characterizes this finite momentum paired phase and should be readily accessible through angle resolved photo emission spectroscopy, quasiparticle interference and differential conductance measurements. Based on the electrical and optical transport properties we capture the non Fermi liquid behavior of these systems at high temperatures, dominated by local superconducting correlations and characterized by resilient quasiparticles which survive the breakdown of the Fermi liquid description. We map out the generic thermal phase diagram of thed-wave Pauli limited superconductors and provide for the first time the accurate estimates of the thermal scales corresponding to the: (a) loss of (quasi) long range superconducting phase coherence (Tc), (b) loss of local pair correlations (Tpg), (c) breakdown of the Fermi liquid theory (Tmax) and cross-over from the non Fermi liquid to the bad metallic phase (TBR). Our thermal phase diagram mapped out on the basis of the spectroscopic and transport properties are found to be in qualitative agreement with the experimental observations on CeCoIn5andκ-BEDT, in terms of the thermodynamic phases and the phase transitions. The results presented in this paper are expected to initiate important transport and spectroscopic experiments on the Pauli limitedd-wave superconductors, providing sharp signatures of the finite momentum Cooper paired state in these materials.
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Affiliation(s)
- Madhuparna Karmakar
- Department of Physics and Nanotechnology, College of Engineering and Technology, SRM Institute of Science and Technology, Kattankulathur, Chennai, 603203, India
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Talantsev EF. Intrinsic Coherence Length Anisotropy in Nickelates and Some Iron-Based Superconductors. MATERIALS (BASEL, SWITZERLAND) 2023; 16:4367. [PMID: 37374551 DOI: 10.3390/ma16124367] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2023] [Revised: 06/11/2023] [Accepted: 06/12/2023] [Indexed: 06/29/2023]
Abstract
Nickelate superconductors, R1-xAxNiO2 (where R is a rare earth metal and A = Sr, Ca), experimentally discovered in 2019, exhibit many unexplained mysteries, such as the existence of a superconducting state with Tc (up to 18 K) in thin films and yet absent in bulk materials. Another unexplained mystery of nickelates is their temperature-dependent upper critical field, Bc2(T), which can be nicely fitted to two-dimensional (2D) models; however, the deduced film thickness, dsc,GL, exceeds the physical film thickness, dsc, by a manifold. To address the latter, it should be noted that 2D models assume that dsc is less than the in-plane and out-of-plane ground-state coherence lengths, dsc<ξab(0) and dsc<ξc(0), respectively, and, in addition, that the inequality ξc(0)<ξab(0) satisfies. Analysis of the reported experimental Bc2(T) data showed that at least one of these conditions does not satisfy for R1-xAxNiO2 films. This implies that nickelate films are not 2D superconductors, despite the superconducting state being observed only in thin films. Based on this, here we propose an analytical three-dimensional (3D) model for a global data fit of in-plane and out-of-plane Bc2(T) in nickelates. The model is based on a heuristic expression for temperature-dependent coherence length anisotropy: γξ(T)=γξ(0)1-1a×TTc, where a>1 is a unitless free-fitting parameter. The proposed expression for γξ(T), perhaps, has a much broader application because it has been successfully applied to bulk pnictide and chalcogenide superconductors.
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Affiliation(s)
- Evgeny F Talantsev
- M. N. Miheev Institute of Metal Physics, Ural Branch, Russian Academy of Sciences, 18, S. Kovalevskoy St., 620108 Ekaterinburg, Russia
- NANOTECH Centre, Ural Federal University, 19 Mira St., 620002 Ekaterinburg, Russia
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Evidence for the Fulde-Ferrell-Larkin-Ovchinnikov state in bulk NbS 2. Nat Commun 2021; 12:3676. [PMID: 34135329 PMCID: PMC8209018 DOI: 10.1038/s41467-021-23976-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Accepted: 05/28/2021] [Indexed: 11/22/2022] Open
Abstract
We present measurements of the magnetic torque, specific heat and thermal expansion of the bulk transition metal dichalcogenide (TMD) superconductor NbS2 in high magnetic fields, with its layer structure aligned strictly parallel to the field using a piezo rotary positioner. The upper critical field of superconducting TMDs in the 2D form is known to be dramatically enhanced by a special form of Ising spin orbit coupling. This Ising superconductivity is very robust to the Pauli paramagnetic effect and can therefore exist beyond the Pauli limit for superconductivity. We find that superconductivity beyond the Pauli limit still exists in bulk single crystals of NbS2 for a precisely parallel field alignment. However, the comparison of our upper critical field transition line with numerical simulations rather points to the development of a Fulde-Ferrell-Larkin-Ovchinnikov state above the Pauli limit as a cause. This is also consistent with the observation of a magnetic field driven phase transition in the thermodynamic quantities within the superconducting state near the Pauli limit. Superconductivity is often destroyed under magnetic field larger than a critical value called Pauli limit. Here, the authors report superconductivity beyond the Pauli limit in bulk single crystals of NbS2, suggesting the development of a Fulde-Ferrell-Larkin-Ovchinnikov state.
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Karmakar M. Pauli limited d-wave superconductors: quantum breached pair phase and thermal transitions. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:405604. [PMID: 32396876 DOI: 10.1088/1361-648x/ab926a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2019] [Accepted: 05/12/2020] [Indexed: 06/11/2023]
Abstract
We report a quantum phase transition in Pauli limited d-wave superconductors and give the mean field estimates of the associated quantum critical point. For a population imbalanced d-wave superconductor a stable ground state phase viz quantum breached pair phase has been identified which comprises of spatial coexistence of gapless superconductivity and nonzero magnetization. Based on the thermodynamic and quasiparticle indicators we for the first time analyze this phase, discuss the thermal behavior of Pauli limited d-wave superconductor, give accurate estimates of the thermal scales associated with such systems and map out the pseudogap regime. Our work shows that while the Pauli limited superconductors are known to exhibit exotic modulated superconducting phase at large imbalance of fermion populations; in the regime of weak imbalance an intriguing phase of competing orders is realized. We have established that rather than the superconducting pairing field, it is the average magnetization of the system that quantifies this quantum phase transition. Given that the existing Pauli limited superconductors possess unconventional pairing state symmetry of the superconducting order, our work promises to open up new avenues in the experimental research of these materials. We have also demonstrated an alternate scenario wherein the quantum breached pair phase is a natural outcome for a d-wave superconductor with unequal effective masses of the fermion species.
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Ayino Y, Yue J, Wang T, Jalan B, Pribiag VS. Effects of paramagnetic pair-breaking and spin-orbital coupling on multi-band superconductivity. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:38LT02. [PMID: 32422615 DOI: 10.1088/1361-648x/ab940c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Accepted: 05/18/2020] [Indexed: 06/11/2023]
Abstract
The BCS picture of superconductivity describes pairing between electrons originating from a single band. A generalization of this picture occurs in multi-band superconductors, where electrons from two or more bands contribute to superconductivity. The contributions of the different bands can result in an overall enhancement of the critical field and can lead to qualitative changes in the temperature dependence of the upper critical field when compared to the single-band case. While the role of orbital pair-breaking on the critical field of multi-band superconductors has been explored extensively, paramagnetic and spin-orbital scattering effects have received comparatively little attention. Here we investigate this problem using thin films of Nd-doped SrTiO3. We furthermore propose a model for analyzing the temperature-dependence of the critical field in the presence of orbital, paramagnetic and spin-orbital effects, and find a very good agreement with our data. Interestingly, we also observe a dramatic enhancement in the out-of-plane critical field to values well in excess of the Chandrasekhar-Clogston (Pauli) paramagnetic limit, which can be understood as a consequence of multi-band effects in the presence of spin-orbital scattering.
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Affiliation(s)
- Yilikal Ayino
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Jin Yue
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Tianqi Wang
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Bharat Jalan
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Vlad S Pribiag
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, United States
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Abstract
Evidence of inhomogeneous superconductivity, in this case superconductivity with a spatially modulated superconducting order parameter, has now been found in many materials and by many measurement methods. Although the evidence is strong, it is circumstantial in the organic superconductors, scant in the pnictides, and complex in the heavy Fermions. However, it is clear some form of exotic superconductivity exists at high fields and low temperatures in many electronically anisotropic superconductors. The evidence is reviewed in this article, and examples of similar measurements are compared across different families of superconductors. An effort is made to find a consistent way to measure the superconducting energy gap across all materials, and use this value to predict the Clogston–Chandrasakhar paramagnetic limit Hp. Methods for predicting the existence of inhomogeneous superconductivity are shown to work for the organic superconductors, and then used to suggest new materials to study.
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Sohn E, Xi X, He WY, Jiang S, Wang Z, Kang K, Park JH, Berger H, Forró L, Law KT, Shan J, Mak KF. An unusual continuous paramagnetic-limited superconducting phase transition in 2D NbSe 2. NATURE MATERIALS 2018; 17:504-508. [PMID: 29713039 DOI: 10.1038/s41563-018-0061-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2017] [Accepted: 03/16/2018] [Indexed: 06/08/2023]
Abstract
Time reversal and spatial inversion are two key symmetries for conventional Bardeen-Cooper-Schrieffer (BCS) superconductivity 1 . Breaking inversion symmetry can lead to mixed-parity Cooper pairing and unconventional superconducting properties1-5. Two-dimensional (2D) NbSe2 has emerged as a new non-centrosymmetric superconductor with the unique out-of-plane or Ising spin-orbit coupling (SOC)6-9. Here we report the observation of an unusual continuous paramagnetic-limited superconductor-normal metal transition in 2D NbSe2. Using tunelling spectroscopy under high in-plane magnetic fields, we observe a continuous closing of the superconducting gap at the upper critical field at low temperatures, in stark contrast to the abrupt first-order transition observed in BCS thin-film superconductors10-12. The paramagnetic-limited continuous transition arises from a large spin susceptibility of the superconducting phase due to the Ising SOC. The result is further supported by self-consistent mean-field calculations based on the ab initio band structure of 2D NbSe2. Our findings establish 2D NbSe2 as a promising platform to explore novel spin-dependent superconducting phenomena and device concepts 1 , such as equal-spin Andreev reflection 13 and topological superconductivity14-16.
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Affiliation(s)
- Egon Sohn
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
- Department of Physics and School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Xiaoxiang Xi
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China
| | - Wen-Yu He
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Shengwei Jiang
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
- Department of Physics and School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Zefang Wang
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
- Department of Physics and School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Kaifei Kang
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
- Department of Physics and School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Ju-Hyun Park
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA
| | - Helmuth Berger
- Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
| | - László Forró
- Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
| | - Kam Tuen Law
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Jie Shan
- Department of Physics, The Pennsylvania State University, University Park, PA, USA.
- Department of Physics and School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA.
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA.
| | - Kin Fai Mak
- Department of Physics, The Pennsylvania State University, University Park, PA, USA.
- Department of Physics and School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA.
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA.
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9
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Ptok A. The influence of the dimensionality of the system on the realization of unconventional Fulde-Ferrell-Larkin-Ovchinnikov pairing in ultra-cold Fermi gases. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:475901. [PMID: 29019340 DOI: 10.1088/1361-648x/aa928d] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The recent development of experimental techniques in ultracold atomic Fermi gases is extremely helpful in the progress of the realization of the unconventional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluid phase in quasi-one dimensional systems (Liao et al 2010 Nature 467 567). Due to a Fermi surface nesting, which is enhanced in 1D, the low-dimensional systems are particularly good candidates to find the FFLO phase stable. We investigate the influence of a dimensional crossover (from one dimension (1D) to two dimensions (2D) or three dimensions (3D)) on the stability of the FFLO state in the spin-imbalanced attractive Hubbard model.
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Affiliation(s)
- Andrzej Ptok
- Institute of Nuclear Physics, Polish Academy of Sciences, ul. E. Radzikowskiego 152, PL-31342 Kraków, Poland. Institute of Physics, Maria Curie-Skłodowska University, Plac M. Skłodowskiej-Curie 1, PL-20031 Lublin, Poland
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10
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Cho CW, Yang JH, Yuan NFQ, Shen J, Wolf T, Lortz R. Thermodynamic Evidence for the Fulde-Ferrell-Larkin-Ovchinnikov State in the KFe_{2}As_{2} Superconductor. PHYSICAL REVIEW LETTERS 2017; 119:217002. [PMID: 29219397 DOI: 10.1103/physrevlett.119.217002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/24/2017] [Indexed: 06/07/2023]
Abstract
We investigate the magnetic phase diagram near the upper critical field of KFe_{2}As_{2} by magnetic torque and specific heat experiments using a high-resolution piezorotary positioner to precisely control the parallel alignment of the magnetic field with respect to the FeAs layers. We observe a clear double transition when the field is strictly aligned in the plane and a characteristic upturn of the upper critical field line, which goes far beyond the Pauli limit at 4.8 T. This provides firm evidence that a Fulde-Ferrell-Larkin-Ovchinnikov state exists in this iron-based KFe_{2}As_{2} superconductor.
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Affiliation(s)
- Chang-Woo Cho
- Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
| | - Jonathan Haiwei Yang
- Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
| | - Noah F Q Yuan
- Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
| | - Junying Shen
- Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
| | - Thomas Wolf
- Institute for Solid State Physics, Karlsruhe Institute of Technology, D-76021 Karlsruhe, Germany
| | - Rolf Lortz
- Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
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11
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In Search of Unambiguous Evidence of the Fulde–Ferrell–Larkin–Ovchinnikov State in Quasi-Low Dimensional Superconductors. CONDENSED MATTER 2017. [DOI: 10.3390/condmat2030030] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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12
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Eilers F, Grube K, Zocco DA, Wolf T, Merz M, Schweiss P, Heid R, Eder R, Yu R, Zhu JX, Si Q, Shibauchi T, Löhneysen HV. Strain-Driven Approach to Quantum Criticality in AFe_{2}As_{2} with A=K, Rb, and Cs. PHYSICAL REVIEW LETTERS 2016; 116:237003. [PMID: 27341252 DOI: 10.1103/physrevlett.116.237003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2015] [Indexed: 06/06/2023]
Abstract
The iron-based superconductors AFe_{2}As_{2} with A=K, Rb, Cs exhibit large Sommerfeld coefficients approaching those of heavy-fermion systems. We have investigated the magnetostriction and thermal expansion of this series to shed light on this unusual behavior. Quantum oscillations of the magnetostriction allow identifying the band-specific quasiparticle masses which by far exceed the band-structure derived masses. The divergence of the Grüneisen ratio derived from thermal expansion indicates that with increasing volume along the series a quantum critical point is approached. The critical fluctuations responsible for the enhancement of the quasiparticle masses appear to weaken the superconducting state.
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Affiliation(s)
- Felix Eilers
- Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany
| | - Kai Grube
- Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany
| | - Diego A Zocco
- Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany
| | - Thomas Wolf
- Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany
| | - Michael Merz
- Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany
| | - Peter Schweiss
- Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany
| | - Rolf Heid
- Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany
| | - Robert Eder
- Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany
| | - Rong Yu
- Department of Physics, Renmin University of China, Beijing 100872, China
| | - Jian-Xin Zhu
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - Qimiao Si
- Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA
| | - Takasada Shibauchi
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561, Japan
- Department of Physics, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Hilbert V Löhneysen
- Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany
- Physikalisches Institut, Karlsruher Institut für Technologie, 76049 Karlsruhe, Germany
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13
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Yu SL, Yao ZJ, Li JX. Consistent picture of the octet-nodal gap and its evolution with doping in heavily overdoped Ba(1-x)KxFe₂As₂. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:505701. [PMID: 26624620 DOI: 10.1088/0953-8984/27/50/505701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We investigate the pairing symmetry in heavily overdoped Ba(1-x)KxFe2As2 based on the spin-fluctuation mechanism. We propose a Fermi-patch mechanism that is different from the conventional Fermi-surface-nesting picture. The exotic octet nodes of the superconducting gap and the unusual evolution of the gap with doping observed by the recent experiments are well explained in a unified manner. We demonstrate that the scattering of electrons on the Fermi patches is mainly responsible for the incommensurate spin fluctuations and consequently the Fermi-surface-dependent multi-gap structure, since the Fermi level is close to the flat band. In addition, we find that a d-wave pairing state will prevail over the s-wave pairing state around the Lifshitz transition point.
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Affiliation(s)
- Shun-Li Yu
- National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China. Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, People's Republic of China
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14
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Ptok A. Multiple phase transitions in Pauli-limited iron-based superconductors. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:482001. [PMID: 26569450 DOI: 10.1088/0953-8984/27/48/482001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Specific heat measurements have been successfully used to probe unconventional superconducting phases in one-band heavy-fermion and organic superconductors. We extend the method to study successive phase transitions in multi-band materials such as iron-based superconductors. The signatures are multiple peaks in the specific heat, at low temperatures and high magnetic field, which can lead to the experimental verification of unconventional superconducting states with non-zero total momentum.
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Affiliation(s)
- Andrzej Ptok
- Institute of Nuclear Physics, Polish Academy of Sciences, ul Radzikowskiego 152, PL-31-342 Kraków, Poland
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15
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Sundar S, Sharath Chandra LS, Chattopadhyay MK, Roy SB. Evidence of multiband superconductivity in the β-phase Mo1-xRex alloys. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:045701. [PMID: 25563211 DOI: 10.1088/0953-8984/27/4/045701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We present a detailed study of the superconducting properties in the β-phase Mo(1-x)Re(x) (x = 0.25 and 0.4) solid solution alloys pursued through magnetization and heat capacity measurements. The temperature dependence of the upper critical field H(C2)(T) in these binary alloys shows a deviation from the prediction of the Werthamer-Helfand-Hohenberg (WHH) theory. The temperature dependence of superfluid density estimated from the variation of lower critical field H(C1) with temperature, cannot be explained within the framework of a single superconducting energy gap. The heat capacity also shows an anomalous feature in its temperature dependence. All these results can be reasonably explained by considering the existence of two superconducting energy gaps in these Mo(1-x)Re(x) alloys. Initial results of electronic structure calculations and resonant photoelectron spectroscopy measurements support this possibility and suggest that the Re-5d like states at the Fermi level may not intermix with the Mo-5p and 5s like states in the β-phase Mo(1-x)Re(x) alloys and contribute quite distinctly to the superconductivity of these alloys.
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Affiliation(s)
- Shyam Sundar
- Homi Bhabha National Institute at RRCAT, Indore, Madhya Pradesh 452 013, India
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