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Tortora L, Tomassucci G, Pugliese GM, Hacisalihoglu MY, Simonelli L, Marini C, Das G, Ishida S, Iyo A, Eisaki H, Mizokawa T, Saini NL. Anisotropic atomic displacements, local orthorhombicity and anomalous local magnetic moment in Ba 0.6K 0.4Fe 2As 2 superconductor. Phys Chem Chem Phys 2024; 26:22454-22462. [PMID: 39140998 DOI: 10.1039/d4cp02345e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/15/2024]
Abstract
We have investigated the in-plane local structure of the Ba0.6K0.4Fe2As2 superconductor by polarized Fe K-edge extended X-ray absorption fine structure (EXAFS) measurements with temperature. The near neighbor bond distances and their stiffness, measured by polarized EXAFS in two orthogonal directions, are different suggesting in-plane anisotropy of the atomic displacements and local orthorhombicity in the title system. The X-ray absorption near edge structure (XANES) spectra reveal anisotropy of valence electronic structure that changes anomalously below ∼100 K. The local iron magnetic moment, measured by Fe Kβ X-ray emission spectroscopy (XES), increases below the anomalous temperature and shows a decrease in the vicinity of the superconducting transition temperature (Tc ∼ 36 K). The results provide a clear evidence of coupled local lattice, electronic and magnetic degrees of freedom to induce possible nematic fluctuations in an optimally hole doped iron-based superconductor.
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Affiliation(s)
- L Tortora
- Dipartimento di Fisica, Universitá di Roma "La Sapienza" - P. le Aldo Moro 2, 00185 Roma, Italy.
| | - G Tomassucci
- Dipartimento di Fisica, Universitá di Roma "La Sapienza" - P. le Aldo Moro 2, 00185 Roma, Italy.
| | - G M Pugliese
- Dipartimento di Fisica, Universitá di Roma "La Sapienza" - P. le Aldo Moro 2, 00185 Roma, Italy.
| | - M Y Hacisalihoglu
- Dipartimento di Fisica, Universitá di Roma "La Sapienza" - P. le Aldo Moro 2, 00185 Roma, Italy.
| | - L Simonelli
- CELLS - ALBA Synchrotron Radiation Facility, Carrer de la Llum 2-26, 08290, Cerdanyola del Valles, Barcelona, Spain
| | - C Marini
- CELLS - ALBA Synchrotron Radiation Facility, Carrer de la Llum 2-26, 08290, Cerdanyola del Valles, Barcelona, Spain
| | - G Das
- Elettra Sincrotrone Trieste, Strada Statale 14, Km 163.5, Basovizza, 34149 Trieste, Italy
| | - S Ishida
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan
| | - A Iyo
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan
| | - H Eisaki
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan
| | - T Mizokawa
- Department of Applied Physics, Waseda University, Tokyo 169-8555, Japan
| | - N L Saini
- Dipartimento di Fisica, Universitá di Roma "La Sapienza" - P. le Aldo Moro 2, 00185 Roma, Italy.
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Bhowmik S, Ghosh A, Chandni U. Emergent phases in graphene flat bands. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2024; 87:096401. [PMID: 39059412 DOI: 10.1088/1361-6633/ad67ed] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Accepted: 07/26/2024] [Indexed: 07/28/2024]
Abstract
Electronic correlations in two-dimensional materials play a crucial role in stabilising emergent phases of matter. The realisation of correlation-driven phenomena in graphene has remained a longstanding goal, primarily due to the absence of strong electron-electron interactions within its low-energy bands. In this context, magic-angle twisted bilayer graphene has recently emerged as a novel platform featuring correlated phases favoured by the low-energy flat bands of the underlying moiré superlattice. Notably, the observation of correlated insulators and superconductivity, and the interplay between these phases have garnered significant attention. A wealth of correlated phases with unprecedented tunability was discovered subsequently, including orbital ferromagnetism, Chern insulators, strange metallicity, density waves, and nematicity. However, a comprehensive understanding of these closely competing phases remains elusive. The ability to controllably twist and stack multiple graphene layers has enabled the creation of a whole new family of moiré superlattices with myriad properties. Here, we review the progress and development achieved so far, encompassing the rich phase diagrams offered by these graphene-based moiré systems. Additionally, we discuss multiple phases recently observed in non-moiré multilayer graphene systems. Finally, we outline future opportunities and challenges for the exploration of hidden phases in this new generation of moiré materials.
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Affiliation(s)
- Saisab Bhowmik
- Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore 560012, India
| | - Arindam Ghosh
- Department of Physics, Indian Institute of Science, Bangalore 560012, India
- Centre for Nano Science and Engineering, Indian Institute of Science, Bangalore 560012, India
| | - U Chandni
- Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore 560012, India
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Wårdh J, Granath M, Wu J, Bollinger AT, He X, Božović I. Colossal transverse magnetoresistance due to nematic superconducting phase fluctuations in a copper oxide. PNAS NEXUS 2023; 2:pgad255. [PMID: 37601309 PMCID: PMC10438889 DOI: 10.1093/pnasnexus/pgad255] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2023] [Accepted: 07/25/2023] [Indexed: 08/22/2023]
Abstract
Electronic anisotropy ("nematicity") has been detected in cuprate superconductors by various experimental techniques. Using angle-resolved transverse resistance (ARTR) measurements, a very sensitive and background-free technique that can detect 0.5% anisotropy in transport, we have observed it also in La2-xSrxCuO4 (LSCO) for 0.02 ≤ x ≤ 0.25. A central enigma in LSCO is the rotation of the nematic director (orientation of the largest longitudinal resistance) with temperature; this has not been seen before in any material. Here, we address this puzzle by measuring the angle-resolved transverse magnetoresistance (ARTMR) in LSCO. We report the discovery of colossal transverse magnetoresistance (CTMR)-an order-of-magnitude drop in the transverse resistivity in the magnetic field of 6 T. We show that the apparent rotation of the nematic director is caused by anisotropic superconducting fluctuations, which are not aligned with the normal electron fluid, consistent with coexisting bond-aligned and diagonal nematic orders. We quantify this by modeling the (magneto-)conductivity as a sum of normal (Drude) and paraconducting (Aslamazov-Larkin) channels but extended to contain anisotropic Drude and Cooper-pair effective mass tensors. Strikingly, the anisotropy of Cooper-pair stiffness is much larger than that of the normal electrons. It grows dramatically on the underdoped side, where the fluctuations become quasi-one-dimensional. Our analysis is general rather than model dependent. Still, we discuss some candidate microscopic models, including coupled strongly-correlated ladders where the transverse (interladder) phase stiffness is low compared with the longitudinal intraladder stiffness, as well as the anisotropic superconducting fluctuations expected close to the transition to a pair-density wave state.
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Affiliation(s)
- Jonatan Wårdh
- Department of Physics, University of Gothenburg, SE-41296 Gothenburg, Sweden
| | - Mats Granath
- Department of Physics, University of Gothenburg, SE-41296 Gothenburg, Sweden
| | - Jie Wu
- Brookhaven National Laboratory, Upton, NY 11973, USA
- Present address: School of Science, Westlake University, Hangzhou, China
| | | | - Xi He
- Department of Chemistry, Yale University, New Haven, CT 06520, USA
- Energy Sciences Institute, Yale University, West Haven, CT 06516, USA
| | - Ivan Božović
- Brookhaven National Laboratory, Upton, NY 11973, USA
- Department of Chemistry, Yale University, New Haven, CT 06520, USA
- Energy Sciences Institute, Yale University, West Haven, CT 06516, USA
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Abstract
In BaNiS2, a Dirac nodal line band structure exists within a two-dimensional Ni square lattice system, in which significant electronic correlation effects are anticipated. Using scanning tunneling microscopy (STM), we discover signs of correlated-electron behavior, namely electronic nematicity appearing as a pair of C2-symmetry striped patterns in the local density-of-states at ∼60 meV above the Fermi energy. In observations of quasiparticle interference, as well as identifying scattering between Dirac cones, we find that the striped patterns in real space stem from a lifting of degeneracy among electron pockets at the Brillouin zone boundary. We infer a momentum-dependent energy shift with d-form factor, which we model numerically within a density wave (DW) equation framework that considers spin-fluctuation-driven nematicity. This suggests an unusual mechanism driving the nematic instability, stemming from only a small perturbation to the Fermi surface, in a system with very low density of states at the Fermi energy. The Dirac points lie at nodes of the d-form factor and are almost unaffected by it. These results highlight BaNiS2 as a unique material in which Dirac electrons and symmetry-breaking electronic correlations coexist.
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Wiecki P, Frachet M, Haghighirad AA, Wolf T, Meingast C, Heid R, Böhmer AE. Emerging symmetric strain response and weakening nematic fluctuations in strongly hole-doped iron-based superconductors. Nat Commun 2021; 12:4824. [PMID: 34376670 PMCID: PMC8355183 DOI: 10.1038/s41467-021-25121-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Accepted: 07/25/2021] [Indexed: 11/18/2022] Open
Abstract
Electronic nematicity is often found in unconventional superconductors, suggesting its relevance for electronic pairing. In the strongly hole-doped iron-based superconductors, the symmetry channel and strength of the nematic fluctuations, as well as the possible presence of long-range nematic order, remain controversial. Here, we address these questions using transport measurements under elastic strain. By decomposing the strain response into the appropriate symmetry channels, we demonstrate the emergence of a giant in-plane symmetric contribution, associated with the growth of both strong electronic correlations and the sensitivity of these correlations to strain. We find weakened remnants of the nematic fluctuations that are present at optimal doping, but no change in the symmetry channel of nematic fluctuations with hole doping. Furthermore, we find no indication of a nematic-ordered state in the AFe2As2 (A = K, Rb, Cs) superconductors. These results revise the current understanding of nematicity in hole-doped iron-based superconductors.
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Affiliation(s)
- P Wiecki
- Karlsruhe Institute of Technology, Institute for Quantum Materials and Technologies, Karlsruhe, Germany
| | - M Frachet
- Karlsruhe Institute of Technology, Institute for Quantum Materials and Technologies, Karlsruhe, Germany
| | - A-A Haghighirad
- Karlsruhe Institute of Technology, Institute for Quantum Materials and Technologies, Karlsruhe, Germany
| | - T Wolf
- Karlsruhe Institute of Technology, Institute for Quantum Materials and Technologies, Karlsruhe, Germany
| | - C Meingast
- Karlsruhe Institute of Technology, Institute for Quantum Materials and Technologies, Karlsruhe, Germany
| | - R Heid
- Karlsruhe Institute of Technology, Institute for Quantum Materials and Technologies, Karlsruhe, Germany
| | - A E Böhmer
- Karlsruhe Institute of Technology, Institute for Quantum Materials and Technologies, Karlsruhe, Germany.
- Institut für Experimentalphysik IV, Ruhr-Universität Bochum, Bochum, Germany.
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Bu K, Zhang W, Fei Y, Zheng Y, Ai F, Wu Z, Wang Q, Wo H, Zhao J, Yin Y. Observation of an electronic order along [110] direction in FeSe. Nat Commun 2021; 12:1385. [PMID: 33654059 PMCID: PMC7925548 DOI: 10.1038/s41467-021-21318-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2019] [Accepted: 01/17/2021] [Indexed: 11/30/2022] Open
Abstract
Multiple ordered states have been observed in unconventional superconductors. Here, we apply scanning tunneling microscopy to probe the intrinsic ordered states in FeSe, the structurally simplest iron-based superconductor. Besides the well-known nematic order along [100] direction, we observe a checkerboard charge order in the iron lattice, which we name a [110] electronic order in FeSe. The [110] electronic order is robust at 77 K, accompanied with the rather weak [100] nematic order. At 4.5 K, The [100] nematic order is enhanced, while the [110] electronic order forms domains with reduced correlation length. In addition, the collective [110] order is gaped around [−40, 40] meV at 4.5 K. The observation of this exotic electronic order may shed new light on the origin of the ordered states in FeSe. Understanding the relation of different electronic orders in high temperature superconductors is of fundamental interest. Here, the authors observe a checkerboard charge order along [110] direction of FeSe.
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Affiliation(s)
- Kunliang Bu
- Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou, China
| | - Wenhao Zhang
- Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou, China
| | - Ying Fei
- Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou, China
| | - Yuan Zheng
- Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou, China
| | - Fangzhou Ai
- Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou, China
| | - Zongxiu Wu
- Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou, China
| | - Qisi Wang
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai, China
| | - Hongliang Wo
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai, China
| | - Jun Zhao
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai, China.,Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China
| | - Yi Yin
- Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou, China. .,Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China.
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Wiecki P, Haghighirad AA, Weber F, Merz M, Heid R, Böhmer AE. Dominant In-Plane Symmetric Elastoresistance in CsFe_{2}As_{2}. PHYSICAL REVIEW LETTERS 2020; 125:187001. [PMID: 33196224 DOI: 10.1103/physrevlett.125.187001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2020] [Revised: 07/15/2020] [Accepted: 09/24/2020] [Indexed: 06/11/2023]
Abstract
We study the elastoresistance of the highly correlated material CsFe_{2}As_{2} in all symmetry channels. Neutralizing its thermal expansion by means of a piezoelectric-based strain cell is demonstrated to be essential. The elastoresistance response in the in-plane symmetric channel is found to be large, while the response in the symmetry-breaking channels is weaker and provides no evidence for a divergent nematic susceptibility. Rather, our results can be interpreted naturally within the framework of a coherence-incoherence crossover, where the low-temperature coherent state is sensitively tuned by the in-plane atomic distances.
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Affiliation(s)
- P Wiecki
- Karlsruhe Institute of Technology, Institute for Quantum Materials and Technologies, 76021 Karlsruhe, Germany
| | - A-A Haghighirad
- Karlsruhe Institute of Technology, Institute for Quantum Materials and Technologies, 76021 Karlsruhe, Germany
| | - F Weber
- Karlsruhe Institute of Technology, Institute for Quantum Materials and Technologies, 76021 Karlsruhe, Germany
| | - M Merz
- Karlsruhe Institute of Technology, Institute for Quantum Materials and Technologies, 76021 Karlsruhe, Germany
| | - R Heid
- Karlsruhe Institute of Technology, Institute for Quantum Materials and Technologies, 76021 Karlsruhe, Germany
| | - A E Böhmer
- Karlsruhe Institute of Technology, Institute for Quantum Materials and Technologies, 76021 Karlsruhe, Germany
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