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Georgiev M, Chamati H. An Exchange Mechanism for the Magnetic Behavior of Er 3+ Complexes. Molecules 2021; 26:molecules26164922. [PMID: 34443510 PMCID: PMC8400239 DOI: 10.3390/molecules26164922] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Revised: 08/03/2021] [Accepted: 08/03/2021] [Indexed: 11/16/2022] Open
Abstract
We study the magnetic properties of the erbium based compounds, Na9[Er(W5O18)2] and [(Pc)Er{Pc{N(C4H9)2}8}]·/-, in the framework of an effective spin exchange model involving delocalized electrons occupying molecular orbitals. The calculations successfully reproduce the experimental data available in the literature for the magnetic spectrum, magnetization and molar susceptibility in dc and ac fields. Owing to their similar molecular geometry, the compounds' magnetic behaviors are interpreted in terms of the same set of active orbitals and thus the same effective spin coupling scheme. For all three complexes, the model predicts a prompt change in the ground state from a Kramer's doublet at zero fields to a fully polarized quartet one brought about by the action of an external magnetic field without Zeeman splitting. This alteration is attributed to the enhancement of the effect of orbital interactions over the spin exchange as the magnitude of the external magnetic field increases.
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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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Chen T, Chen Y, Kreisel A, Lu X, Schneidewind A, Qiu Y, Park JT, Perring TG, Stewart JR, Cao H, Zhang R, Li Y, Rong Y, Wei Y, Andersen BM, Hirschfeld PJ, Broholm C, Dai P. Anisotropic spin fluctuations in detwinned FeSe. NATURE MATERIALS 2019; 18:709-716. [PMID: 31110345 PMCID: PMC7895486 DOI: 10.1038/s41563-019-0369-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Accepted: 04/10/2019] [Indexed: 05/05/2023]
Abstract
Superconductivity in FeSe emerges from a nematic phase that breaks four-fold rotational symmetry in the iron plane. This phase may arise from orbital ordering, spin fluctuations or hidden magnetic quadrupolar order. Here we use inelastic neutron scattering on a mosaic of single crystals of FeSe, detwinned by mounting on a BaFe2As2 substrate to demonstrate that spin excitations are most intense at the antiferromagnetic wave vectors QAF = (±1, 0) at low energies E = 6-11 meV in the normal state. This two-fold (C2) anisotropy is reduced at lower energies, 3-5 meV, indicating a gapped four-fold (C4) mode. In the superconducting state, however, the strong nematic anisotropy is again reflected in the spin resonance (E = 3.6 meV) at QAF with incommensurate scattering around 5-6 meV. Our results highlight the extreme electronic anisotropy of the nematic phase of FeSe and are consistent with a highly anisotropic superconducting gap driven by spin fluctuations.
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Affiliation(s)
- Tong Chen
- Department of Physics and Astronomy, Rice University, Houston, TX, USA
| | - Youzhe Chen
- Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD, USA
| | - Andreas Kreisel
- Institut für Theoretische Physik, Universität Leipzig, Leipzig, Germany
| | - Xingye Lu
- Center for Advanced Quantum Studies and Department of Physics, Beijing Normal University, Beijing, China.
| | - Astrid Schneidewind
- Forschungszentrum Jülich GmbH, Jülich Center for Neutron Sciences at MLZ, Garching, Germany
| | - Yiming Qiu
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, USA
| | - J T Park
- Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München, Garching, Germany
| | - Toby G Perring
- ISIS Facility, STFC Rutherford-Appleton Laboratory, Didcot, UK
| | - J Ross Stewart
- ISIS Facility, STFC Rutherford-Appleton Laboratory, Didcot, UK
| | - Huibo Cao
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
| | - Rui Zhang
- Department of Physics and Astronomy, Rice University, Houston, TX, USA
| | - Yu Li
- Department of Physics and Astronomy, Rice University, Houston, TX, USA
| | - Yan Rong
- Center for Advanced Quantum Studies and Department of Physics, Beijing Normal University, Beijing, China
| | - Yuan Wei
- Institute of Physics, Chinese Academy of Sciences, Beijing, China
| | - Brian M Andersen
- Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
| | - P J Hirschfeld
- Department of Physics, University of Florida, Gainesville, FL, USA
| | - Collin Broholm
- Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD, USA
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, USA
| | - Pengcheng Dai
- Department of Physics and Astronomy, Rice University, Houston, TX, USA.
- Center for Advanced Quantum Studies and Department of Physics, Beijing Normal University, Beijing, China.
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She JH, Lawler MJ, Kim EA. Quantum Spin Liquid Intertwining Nematic and Superconducting Order in Fese. PHYSICAL REVIEW LETTERS 2018; 121:237002. [PMID: 30576170 DOI: 10.1103/physrevlett.121.237002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Revised: 02/19/2018] [Indexed: 06/09/2023]
Abstract
Despite its seemingly simple composition and structure, the pairing mechanism of FeSe remains an open problem due to several striking phenomena. Among them are nematic order without magnetic order, nodeless gap and unusual inelastic neutron spectra with a broad continuum, and gap anisotropy consistent with orbital selection of unknown origin. Here we propose a microscopic description of a nematic quantum spin liquid that reproduces key features of neutron spectra. We then study how the spin fluctuations of the local moments lead to pairing within a spin-fermion model. We find the resulting superconducting order parameter to be nodeless s±d wave within each domain. Further we show that orbital dependent Kondo-like coupling can readily capture observed gap anisotropy. Our prediction calls for inelastic neutron scattering in a detwinned sample.
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Affiliation(s)
- Jian-Huang She
- Department of Physics, Cornell University, Ithaca, New York 14853, USA
| | - Michael J Lawler
- Department of Physics, Cornell University, Ithaca, New York 14853, USA
- Department of physics, Binghamton University, Vestal, New York 13850, USA
- Kavli Institute for Theoretical Physics, Kohn Hall, University of California, Santa Barbara, California 93106-4030, USA
| | - Eun-Ah Kim
- Department of Physics, Cornell University, Ithaca, New York 14853, USA
- Kavli Institute for Theoretical Physics, Kohn Hall, University of California, Santa Barbara, California 93106-4030, USA
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Böhmer AE, Kreisel A. Nematicity, magnetism and superconductivity in FeSe. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:023001. [PMID: 29240560 DOI: 10.1088/1361-648x/aa9caa] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Iron-based superconductors are well known for their complex interplay between structure, magnetism and superconductivity. FeSe offers a particularly fascinating example. This material has been intensely discussed because of its extended nematic phase, whose relationship with magnetism is not obvious. Superconductivity in FeSe is highly tunable, with the superconducting transition temperature, T c, ranging from 8 K in bulk single crystals at ambient pressure to almost 40 K under pressure or in intercalated systems, and to even higher temperatures in thin films. In this topical review, we present an overview of nematicity, magnetism and superconductivity, and discuss the interplay of these phases in FeSe. We focus on bulk FeSe and the effects of physical pressure and chemical substitutions as tuning parameters. The experimental results are discussed in the context of the well-studied iron-pnictide superconductors and interpretations from theoretical approaches are presented.
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Affiliation(s)
- Anna E Böhmer
- Ames Laboratory, US DOE, Ames, IA 50011, United States of America
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