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Philippe JC, Lespinas A, Faria J, Forget A, Colson D, Houver S, Cazayous M, Sacuto A, Paul I, Gallais Y. Nematic-Fluctuation-Mediated Superconductivity Revealed by Anisotropic Strain in Ba(Fe_{1-x}Co_{x})_{2}As_{2}. PHYSICAL REVIEW LETTERS 2022; 129:187002. [PMID: 36374691 DOI: 10.1103/physrevlett.129.187002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2022] [Revised: 09/10/2022] [Accepted: 10/05/2022] [Indexed: 06/16/2023]
Abstract
Anisotropic strain is an external field capable of selectively addressing the role of nematic fluctuations in promoting superconductivity. We demonstrate this using polarization-resolved elasto-Raman scattering by probing the evolution of nematic fluctuations under strain in the normal and superconducting state of the paradigmatic iron-based superconductor Ba(Fe_{1-x}Co_{x})_{2}As_{2}. In the parent compound BaFe_{2}As_{2} we observe a strain-induced suppression of the nematic susceptibility which follows the expected behavior of an Ising order parameter under a symmetry breaking field. For the superconducting compound, the suppression of the nematic susceptibility correlates with the decrease of the critical temperature T_{c}, indicating a significant contribution of nematic fluctuations to electron pairing. Our results validate theoretical scenarios of enhanced T_{c} near a nematic quantum critical point.
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Affiliation(s)
- Jean-Côme Philippe
- Université Paris Cité, Matériaux et Phénomènes Quantiques, UMR CNRS 7162, Bátiment Condorcet, 75205 Paris Cedex 13, France
| | - Alexis Lespinas
- Université Paris Cité, Matériaux et Phénomènes Quantiques, UMR CNRS 7162, Bátiment Condorcet, 75205 Paris Cedex 13, France
| | - Jimmy Faria
- Université Paris Cité, Matériaux et Phénomènes Quantiques, UMR CNRS 7162, Bátiment Condorcet, 75205 Paris Cedex 13, France
| | - Anne Forget
- Service de Physique de l'Etat Condensé, DSM/DRECAM/SPEC, CEA Saclay, Gif-sur-Yvette 91191, France
| | - Dorothée Colson
- Service de Physique de l'Etat Condensé, DSM/DRECAM/SPEC, CEA Saclay, Gif-sur-Yvette 91191, France
| | - Sarah Houver
- Université Paris Cité, Matériaux et Phénomènes Quantiques, UMR CNRS 7162, Bátiment Condorcet, 75205 Paris Cedex 13, France
| | - Maximilien Cazayous
- Université Paris Cité, Matériaux et Phénomènes Quantiques, UMR CNRS 7162, Bátiment Condorcet, 75205 Paris Cedex 13, France
| | - Alain Sacuto
- Université Paris Cité, Matériaux et Phénomènes Quantiques, UMR CNRS 7162, Bátiment Condorcet, 75205 Paris Cedex 13, France
| | - Indranil Paul
- Université Paris Cité, Matériaux et Phénomènes Quantiques, UMR CNRS 7162, Bátiment Condorcet, 75205 Paris Cedex 13, France
| | - Yann Gallais
- Université Paris Cité, Matériaux et Phénomènes Quantiques, UMR CNRS 7162, Bátiment Condorcet, 75205 Paris Cedex 13, France
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Pimenov D, Kamenev A, Chubukov AV. Quasiparticle Scattering in a Superconductor near a Nematic Critical Point: Resonance Mode and Multiple Attractive Channels. PHYSICAL REVIEW LETTERS 2022; 128:017001. [PMID: 35061475 DOI: 10.1103/physrevlett.128.017001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Accepted: 12/01/2021] [Indexed: 06/14/2023]
Abstract
We analyze the scattering rate for 2D fermions interacting via soft nematic fluctuations. The ground state is an s-wave superconductor, but other pairing channels are almost equally attractive. This strongly alters the scattering rate: At energies beyond the pairing gap Δ, it is renormalized by contributions from all pairing channels. At energies of order Δ, it is determined by the competition between scattering into a gapped continuum and dispersing nematic resonance. The outcome is a "peak-peak-dip-hump" spectrum, similar, but not identical, to the "peak-dip-hump" structure in the cuprates.
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Affiliation(s)
- Dimitri Pimenov
- William I. Fine Theoretical Physics Institute, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Alex Kamenev
- William I. Fine Theoretical Physics Institute, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Andrey V Chubukov
- William I. Fine Theoretical Physics Institute, University of Minnesota, Minneapolis, Minnesota 55455, USA
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Iron pnictides and chalcogenides: a new paradigm for superconductivity. Nature 2022; 601:35-44. [PMID: 34987212 DOI: 10.1038/s41586-021-04073-2] [Citation(s) in RCA: 30] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Accepted: 09/29/2021] [Indexed: 11/09/2022]
Abstract
Superconductivity is a remarkably widespread phenomenon that is observed in most metals cooled to very low temperatures. The ubiquity of such conventional superconductors, and the wide range of associated critical temperatures, is readily understood in terms of the well-known Bardeen-Cooper-Schrieffer theory. Occasionally, however, unconventional superconductors are found, such as the iron-based materials, which extend and defy this understanding in unexpected ways. In the case of the iron-based superconductors, this includes the different ways in which the presence of multiple atomic orbitals can manifest in unconventional superconductivity, giving rise to a rich landscape of gap structures that share the same dominant pairing mechanism. In addition, these materials have also led to insights into the unusual metallic state governed by the Hund's interaction, the control and mechanisms of electronic nematicity, the impact of magnetic fluctuations and quantum criticality, and the importance of topology in correlated states. Over the fourteen years since their discovery, iron-based superconductors have proven to be a testing ground for the development of novel experimental tools and theoretical approaches, both of which have extensively influenced the wider field of quantum materials.
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Quadrupolar charge dynamics in the nonmagnetic FeSe 1-x S x superconductors. Proc Natl Acad Sci U S A 2021; 118:2020585118. [PMID: 33980712 DOI: 10.1073/pnas.2020585118] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We use polarization-resolved electronic Raman spectroscopy to study quadrupolar charge dynamics in a nonmagnetic [Formula: see text] superconductor. We observe two types of long-wavelength [Formula: see text] symmetry excitations: 1) a low-energy quasi-elastic scattering peak (QEP) and 2) a broad electronic continuum with a maximum at 55 meV. Below the tetragonal-to-orthorhombic structural transition at [Formula: see text], a pseudogap suppression with temperature dependence reminiscent of the nematic order parameter develops in the [Formula: see text] symmetry spectra of the electronic excitation continuum. The QEP exhibits critical enhancement upon cooling toward [Formula: see text] The intensity of the QEP grows with increasing sulfur concentration x and maximizes near critical concentration [Formula: see text], while the pseudogap size decreases with the suppression of [Formula: see text] We interpret the development of the pseudogap in the quadrupole scattering channel as a manifestation of transition from the non-Fermi liquid regime, dominated by strong Pomeranchuk-like fluctuations giving rise to intense electronic continuum of excitations in the fourfold symmetric high-temperature phase, to the Fermi liquid regime in the broken-symmetry nematic phase where the quadrupole fluctuations are suppressed.
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He G, Li D, Jost D, Baum A, Shen PP, Dong XL, Zhao ZX, Hackl R. Raman Study of Cooper Pairing Instabilities in (Li_{1-x}Fe_{x})OHFeSe. PHYSICAL REVIEW LETTERS 2020; 125:217002. [PMID: 33274977 DOI: 10.1103/physrevlett.125.217002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2020] [Accepted: 10/15/2020] [Indexed: 06/12/2023]
Abstract
We studied the electronic Raman spectra of (Li_{1-x}Fe_{x})OHFeSe as a function of light polarization and temperature. In the B_{1g} spectra alone we observe the redistribution of spectral weight expected for a superconductor and two well-resolved peaks below T_{c}. The nearly resolution-limited peak at 110 cm^{-1} (13.6 meV) is identified as a collective mode. The peak at 190 cm^{-1} (23.6 meV) is presumably another collective mode since the line is symmetric and its energy is significantly below the gap energy observed by single-particle spectroscopies. Given the experimental band structure of (Li_{1-x}Fe_{x})OHFeSe, the most plausible explanations include conventional spin-fluctuation pairing between the electron bands and the incipient hole band and pairing between the hybridized electron bands. The absence of gap features in A_{1g} and B_{2g} symmetry favors the second case. Thus, in spite of various differences between the pnictides and chalcogenides, this Letter demonstrates the proximity of pairing states and the importance of band structure effects in the Fe-based compounds.
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Affiliation(s)
- G He
- Walther Meissner Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany
| | - D Li
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - D Jost
- Walther Meissner Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany
- Fakultät für Physik E23, Technische Universität München, 85748 Garching, Germany
| | - A Baum
- Walther Meissner Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany
| | - P P Shen
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - X L Dong
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - Z X Zhao
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - R Hackl
- Walther Meissner Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany
- Fakultät für Physik E23, Technische Universität München, 85748 Garching, Germany
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Abstract
Emergent electronic phenomena in iron-based superconductors have been at the forefront of condensed matter physics for more than a decade. Much has been learned about the origins and intertwined roles of ordered phases, including nematicity, magnetism, and superconductivity, in this fascinating class of materials. In recent years, focus has been centered on the peculiar and highly unusual properties of FeSe and its close cousins. This family of materials has attracted considerable attention due to the discovery of unexpected superconducting gap structures, a wide range of superconducting critical temperatures, and evidence for nontrivial band topology, including associated spin-helical surface states and vortex-induced Majorana bound states. Here, we review superconductivity in iron chalcogenide superconductors, including bulk FeSe, doped bulk FeSe, FeTe1−xSex, intercalated FeSe materials, and monolayer FeSe and FeTe1−xSex on SrTiO3. We focus on the superconducting properties, including a survey of the relevant experimental studies, and a discussion of the different proposed theoretical pairing scenarios. In the last part of the paper, we review the growing recent evidence for nontrivial topological effects in FeSe-related materials, focusing again on interesting implications for superconductivity.
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Lazarević N, Hackl R. Fluctuations and pairing in Fe-based superconductors: light scattering experiments. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:413001. [PMID: 32272462 DOI: 10.1088/1361-648x/ab8849] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2019] [Accepted: 04/09/2020] [Indexed: 06/11/2023]
Abstract
Inelastic scattering of visible light (Raman effect) offers a window into properties of correlated metals such as spin, electron and lattice dynamics as well as their mutual interactions. In this review we focus on electronic and spin excitations in Fe-based pnictides and chalcogenides, in particular but not exclusively superconductors. After a general introduction to the basic theory including the selection rules for the various scattering processes we provide an overview over the major experimental results. In the superconducting state below the transition temperatureTcthe pair-breaking effect can be observed, and the gap energies may be derived and associated with the gaps on the electron and hole bands. In spite of the similarities of the overall band structures the results are strongly dependent on the family and may even change qualitatively within one family. In some of the compounds strong collective modes appear belowTc. In Ba1-xKxFe2As2, which has the most isotropic gap of all Fe-based superconductors, there are indications that these modes are exciton-like states appearing in the presence of a hierarchy of pairing tendencies. The strong in-gap modes observed in Co-doped NaFeAs are interpreted in terms of quadrupolar orbital excitations which become undamped in the superconducting state. The doping dependence of the scattering intensity in Ba(Fe1-xCox)2As2is associated with a nematic resonance above a quantum critical point and interpreted in terms of a critical enhancement at the maximalTc. In the normal state the response from particle-hole excitations reflects the resistivity. In addition, there are strongly temperature-dependent contributions from presumably critical fluctuations in the energy range ofkBTwhich can be compared to the elastic properties. Currently it is not settled whether the fluctuations observed by light scattering are related to spin or charge. Another controversy relates to putative two-magnon excitations, typically in the energy range below 0.5 eV. Whereas this response presumably originates from charge excitations in most of the Fe-based compounds theory and experiment suggest that the excitations in the 60 meV range in FeSe stem from localized spins in a nearly frustrated system.
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Affiliation(s)
- N Lazarević
- Center for Solid State Physics and New Materials, Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, 11080 Belgrade, Serbia
| | - R Hackl
- Walther Meissner Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany
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Maiti S, Maier TA, Böhm T, Hackl R, Hirschfeld PJ. Probing the Pairing Interaction and Multiple Bardasis-Schrieffer Modes Using Raman Spectroscopy. PHYSICAL REVIEW LETTERS 2016; 117:257001. [PMID: 28036201 DOI: 10.1103/physrevlett.117.257001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Indexed: 06/06/2023]
Abstract
In unconventional superconductors, understanding the form of the pairing interaction is the primary goal. In this regard, Raman spectroscopy is a very useful tool, as it identifies the ground state and also the subleading pairing channels by probing collective modes. Here, we propose a general theory for a multiband Raman response and identify new features in the spectrum that can provide a robust test for a pairing theory. We identify multiple Bardasis-Schrieffer type collective modes and connect the weights of these modes to the subleading gap structures within a microscopic pairing theory. While our conclusions are completely general, we apply our approach to interpret the specific case of B_{1g} Raman scattering in hole-doped BaFe_{2}As_{2}.
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Affiliation(s)
- S Maiti
- Department of Physics, University of Florida, Gainesville, Florida 32611
| | - T A Maier
- Center for Nanophase Materials Sciences and Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6494, USA
| | - T Böhm
- Walther Meissner Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany
- Fakultät für Physik E23, Technische Universität München, 85748 Garching, Germany
| | - R Hackl
- Walther Meissner Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany
| | - P J Hirschfeld
- Department of Physics, University of Florida, Gainesville, Florida 32611
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Massat P, Farina D, Paul I, Karlsson S, Strobel P, Toulemonde P, Méasson MA, Cazayous M, Sacuto A, Kasahara S, Shibauchi T, Matsuda Y, Gallais Y. Charge-induced nematicity in FeSe. Proc Natl Acad Sci U S A 2016; 113:9177-81. [PMID: 27482118 PMCID: PMC4995930 DOI: 10.1073/pnas.1606562113] [Citation(s) in RCA: 72] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The spontaneous appearance of nematicity, a state of matter that breaks rotation but not translation symmetry, is one of the most intriguing properties of the iron-based superconductors (Fe SC), and has relevance for the cuprates as well. Establishing the critical electronic modes behind nematicity remains a challenge, however, because their associated susceptibilities are not easily accessible by conventional probes. Here, using FeSe as a model system, and symmetry-resolved electronic Raman scattering as a probe, we unravel the presence of critical charge nematic fluctuations near the structural/nematic transition temperature, [Formula: see text] 90 K. The diverging behavior of the associated nematic susceptibility foretells the presence of a Pomeranchuk instability of the Fermi surface with d-wave symmetry. The excellent scaling between the observed nematic susceptibility and elastic modulus data demonstrates that the structural distortion is driven by this d-wave Pomeranchuk transition. Our results make a strong case for charge-induced nematicity in FeSe.
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Affiliation(s)
- Pierre Massat
- Laboratoire Matériaux et Phénomènes Quantiques, CNRS UMR7162, Université Paris Diderot, Paris Cedex 13, France
| | - Donato Farina
- Laboratoire Matériaux et Phénomènes Quantiques, CNRS UMR7162, Université Paris Diderot, Paris Cedex 13, France
| | - Indranil Paul
- Laboratoire Matériaux et Phénomènes Quantiques, CNRS UMR7162, Université Paris Diderot, Paris Cedex 13, France
| | - Sandra Karlsson
- Institut Néél, CNRS Unité Propre de Recherche 2940, 38042 Grenoble, France; Institut Néél, Université Grenoble Alpes, 38042 Grenoble, France
| | - Pierre Strobel
- Institut Néél, CNRS Unité Propre de Recherche 2940, 38042 Grenoble, France; Institut Néél, Université Grenoble Alpes, 38042 Grenoble, France
| | - Pierre Toulemonde
- Institut Néél, CNRS Unité Propre de Recherche 2940, 38042 Grenoble, France; Institut Néél, Université Grenoble Alpes, 38042 Grenoble, France
| | - Marie-Aude Méasson
- Laboratoire Matériaux et Phénomènes Quantiques, CNRS UMR7162, Université Paris Diderot, Paris Cedex 13, France
| | - Maximilien Cazayous
- Laboratoire Matériaux et Phénomènes Quantiques, CNRS UMR7162, Université Paris Diderot, Paris Cedex 13, France
| | - Alain Sacuto
- Laboratoire Matériaux et Phénomènes Quantiques, CNRS UMR7162, Université Paris Diderot, Paris Cedex 13, France
| | | | - Takasada Shibauchi
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561, Japan
| | - Yuji Matsuda
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Yann Gallais
- Laboratoire Matériaux et Phénomènes Quantiques, CNRS UMR7162, Université Paris Diderot, Paris Cedex 13, France;
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