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Kim JJ, Park MS, Lee KS, Joo SH, Yoo JH, Bhoi D, Min BH, Kim KH, Lee J. Observations of Nematicity, Dopants, and Zero-Bias Conductance Peaks for the Ca 0.9La 0.1FeAs 2 Superconductor. NANOMATERIALS (BASEL, SWITZERLAND) 2023; 13:622. [PMID: 36838990 PMCID: PMC9962653 DOI: 10.3390/nano13040622] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Revised: 01/30/2023] [Accepted: 01/31/2023] [Indexed: 06/18/2023]
Abstract
Ca1-xLaxFeAs2 (CLFA112) belongs to a new family of Fe-based superconductors (FeSCs) and has a unique crystal structure featuring an arsenic zigzag chain layer, which has been proposed to be a possible two-dimensional topological insulator. This suggests that CLFA112 is a potential topological superconductor-a platform to realize Majorana fermions. Up to now, even a clear superconducting (SC) gap in CLFA112 has never been observed, and the SC properties of CLFA112 remain largely elusive. In this letter, we report the results of an atomic-scale investigation of the electronic structure of CLFA112 crystals using low-temperature scanning tunneling microscopy (STM). We revealed four different types of surfaces exhibiting distinct electronic properties, with all surfaces displaying dominating 2 × 1 surface reconstructions. On a Ca/La layer on top of an FeAs layer, a clear SC gap of ~12 mV was observed only at the crevices (vacancies) where the FeAs layer can be directly accessed. Remarkably, the FeAs termination layer displayed a dispersing nematic modulation both in real and q space. We also present peculiar zero-bias conductance peaks for the very As chain layer that is believed to exhibit a topological edge state as well as the influence of La dopants on the As chain layer.
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Affiliation(s)
- Jae-Joon Kim
- Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea
- Samsung Electronics Semiconductor R&D Center, Hwaseong-si 18448, Gyeonggi-do, Republic of Korea
| | - Min Seok Park
- Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea
| | - Kyoung Seok Lee
- Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea
- Samsung Electronics Semiconductor R&D Center, Hwaseong-si 18448, Gyeonggi-do, Republic of Korea
| | - Sang Hyun Joo
- Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea
- Samsung Electronics Semiconductor R&D Center, Hwaseong-si 18448, Gyeonggi-do, Republic of Korea
| | - Jung Hoon Yoo
- Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea
| | - Dilip Bhoi
- Center for Novel States of Complex Materials Research, Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea
| | - Byeong Hun Min
- Center for Novel States of Complex Materials Research, Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea
| | - Kee Hoon Kim
- Center for Novel States of Complex Materials Research, Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea
| | - Jinho Lee
- Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea
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Manikandan K, Pervin R, Saravanan C, Sathiskumar M, Chakraborty N, Shirage PM, Mondal S, Srihari V, Poswal HK, Arumugam S. Influence of pressure on the transport, magnetic, and structural properties of superconducting Cr 0.0009NbSe 2 single crystal. RSC Adv 2020; 10:13112-13125. [PMID: 35492110 PMCID: PMC9051428 DOI: 10.1039/c9ra09603e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2019] [Accepted: 02/07/2020] [Indexed: 11/21/2022] Open
Abstract
We investigate the superconducting critical current density (J c), transition temperature (T c), and flux pinning properties under hydrostatic pressure (P) for Cr0.0009NbSe2 single crystal. The application of P enhances T c in both electrical resistivity (∼0.38 K GPa-1: 0 ≤ P ≤ 2.5 GPa) and magnetization (∼0.98 K GPa-1: 0 ≤ P ≤ 1 GPa) measurements, which leads to a monotonic increase in J c and flux pinning properties. The field-dependent J c at various temperatures under P is analyzed within the collecting pinning theory and it shows that δT c pinning is the crossover to δl pinning above the critical pressure (P c ∼0.3 GPa). Our systematic analysis of the flux pinning mechanism indicates that both the density of pinning centers and pinning forces greatly increase with the application of P, which leads to an enhancement in the vortex state. Structural studies using synchrotron X-ray diffraction under pressure illustrate a stable hexagonal phase without any significant impurity phase and lattice parameter reduction with P shows highly anisotropic nature.
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Affiliation(s)
- K Manikandan
- Centre for High Pressure Research, School of Physics, Bharathidasan University Tiruchirappalli-620024 India +91 431 2407045 +91 431 2407118 +91 9500910310
| | - Rukshana Pervin
- Discipline of Metallurgy Engineering and Materials Science & Physics, Indian Institute of Technology Indore Simrol Campus, Khandwa Road Indore 453552 India
| | - C Saravanan
- Centre for High Pressure Research, School of Physics, Bharathidasan University Tiruchirappalli-620024 India +91 431 2407045 +91 431 2407118 +91 9500910310
| | - M Sathiskumar
- Centre for High Pressure Research, School of Physics, Bharathidasan University Tiruchirappalli-620024 India +91 431 2407045 +91 431 2407118 +91 9500910310
| | - Nirman Chakraborty
- CSIR-Central Glass and Ceramic Research Institute Jadavpur Kolkata 700 032 India
| | - Parasharam M Shirage
- Discipline of Metallurgy Engineering and Materials Science & Physics, Indian Institute of Technology Indore Simrol Campus, Khandwa Road Indore 453552 India
| | - Swastik Mondal
- CSIR-Central Glass and Ceramic Research Institute Jadavpur Kolkata 700 032 India
| | - Velaga Srihari
- High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre Mumbai 400085 India
| | - Himanshu Kumar Poswal
- High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre Mumbai 400085 India
| | - S Arumugam
- Centre for High Pressure Research, School of Physics, Bharathidasan University Tiruchirappalli-620024 India +91 431 2407045 +91 431 2407118 +91 9500910310
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Lenz B, Martins C, Biermann S. Spectral functions of Sr 2IrO 4: theory versus experiment. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:293001. [PMID: 30921786 DOI: 10.1088/1361-648x/ab146a] [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
The spin-orbit Mott insulator Sr2IrO4 has attracted a lot of interest in recent years from theory and experiment due to its close connection to isostructural high-temperature copper oxide superconductors. Despite not being superconductive, its spectral features closely resemble those of the cuprates, including Fermi surface and pseudogap properties. In this article, we review and extend recent work in the theoretical description of the spectral function of pure and electron-doped Sr2IrO4 based on a cluster extension of dynamical mean-field theory ('oriented-cluster DMFT') and compare it to available angle-resolved photoemission data. Current theories provide surprisingly good agreement for pure and electron-doped Sr2IrO4, both in the paramagnetic and antiferromagnetic phases. Most notably, one obtains simple explanations for the experimentally observed steep feature around the M point and the pseudo-gap-like spectral feature in electron-doped Sr2IrO4.
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Affiliation(s)
- B Lenz
- CPHT, Ecole Polytechnique, CNRS, Université Paris-Saclay, Route de Saclay, 91128 Palaiseau, France
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Martins C, Aichhorn M, Biermann S. Coulomb correlations in 4d and 5d oxides from first principles-or how spin-orbit materials choose their effective orbital degeneracies. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:263001. [PMID: 28262638 DOI: 10.1088/1361-648x/aa648f] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The interplay of spin-orbit coupling and Coulomb correlations has become a hot topic in condensed matter theory and is especially important in 4d and 5d transition metal oxides, like iridates or rhodates. Here, we review recent advances in dynamical mean-field theory (DMFT)-based electronic structure calculations for treating such compounds, introducing all necessary implementation details. We also discuss the evaluation of Hubbard interactions in spin-orbit materials. As an example, we perform DMFT calculations on insulating strontium iridate (Sr2IrO4) and its 4d metallic counterpart, strontium rhodate (Sr2RhO4). While a Mott-insulating state is obtained for Sr2IrO4 in its paramagnetic phase, the spectral properties and Fermi surfaces obtained for Sr2RhO4 show excellent agreement with available experimental data. Finally, we discuss the electronic structure of these two compounds by introducing the notion of effective spin-orbital degeneracy as the key quantity that determines the correlation strength. We stress that effective spin-orbital degeneracy introduces an additional axis into the conventional picture of a phase diagram based on filling and on the ratio of interactions to bandwidth, analogous to the degeneracy-controlled Mott transition in d1 perovskites.
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Affiliation(s)
- C Martins
- Laboratoire de Chimie et Physique Quantiques, UMR 5626, Université Paul Sabatier, 118 route de Narbonne, 31400 Toulouse, France
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Misawa T, Nomura Y, Biermann S, Imada M. Self-optimized superconductivity attainable by interlayer phase separation at cuprate interfaces. SCIENCE ADVANCES 2016; 2:e1600664. [PMID: 27482542 PMCID: PMC4966878 DOI: 10.1126/sciadv.1600664] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/28/2016] [Accepted: 06/29/2016] [Indexed: 06/06/2023]
Abstract
Stabilizing superconductivity at high temperatures and elucidating its mechanism have long been major challenges of materials research in condensed matter physics. Meanwhile, recent progress in nanostructuring offers unprecedented possibilities for designing novel functionalities. Above all, thin films of cuprate and iron-based high-temperature superconductors exhibit remarkably better superconducting characteristics (for example, higher critical temperatures) than in the bulk, but the underlying mechanism is still not understood. Solving microscopic models suitable for cuprates, we demonstrate that, at an interface between a Mott insulator and an overdoped nonsuperconducting metal, the superconducting amplitude is always pinned at the optimum achieved in the bulk, independently of the carrier concentration in the metal. This is in contrast to the dome-like dependence in bulk superconductors but consistent with the astonishing independence of the critical temperature from the carrier density x observed at the interfaces of La2CuO4 and La2-x Sr x CuO4. Furthermore, we identify a self-organization mechanism as responsible for the pinning at the optimum amplitude: An emergent electronic structure induced by interlayer phase separation eludes bulk phase separation and inhomogeneities that would kill superconductivity in the bulk. Thus, interfaces provide an ideal tool to enhance and stabilize superconductivity. This interfacial example opens up further ways of shaping superconductivity by suppressing competing instabilities, with direct perspectives for designing devices.
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Affiliation(s)
- Takahiro Misawa
- Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Yusuke Nomura
- Centre de Physique Théorique, École Polytechnique, CNRS, Université Paris-Saclay, F-91128 Palaiseau, France
| | - Silke Biermann
- Centre de Physique Théorique, École Polytechnique, CNRS, Université Paris-Saclay, F-91128 Palaiseau, France
| | - Masatoshi Imada
- Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
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