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Hu B, Chen H, Ye Y, Huang Z, Han X, Zhao Z, Xiao H, Lin X, Yang H, Wang Z, Gao HJ. Evidence of a distinct collective mode in Kagome superconductors. Nat Commun 2024; 15:6109. [PMID: 39030195 PMCID: PMC11271580 DOI: 10.1038/s41467-024-50330-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2024] [Accepted: 07/05/2024] [Indexed: 07/21/2024] Open
Abstract
The collective modes of the superconducting order parameter fluctuation can provide key insights into the nature of the superconductor. Recently, a family of superconductors has emerged in non-magnetic kagome materials AV3Sb5 (A = K, Rb, Cs), exhibiting fertile emergent phenomenology. However, the collective behaviors of Cooper pairs have not been studied. Here, we report a distinct collective mode in CsV3-xTaxSb5 using scanning tunneling microscope/spectroscopy. The spectral line-shape is well-described by one isotropic and one anisotropic superconducting gap, and a bosonic mode due to electron-mode coupling. With increasing x, the two gaps move closer in energy, merge into two isotropic gaps of equal amplitude, and then increase synchronously. The mode energy decreases monotonically to well below 2 Δ and survives even after the charge density wave order is suppressed. We propose the interpretation of this collective mode as Leggett mode between different superconducting components or the Bardasis-Schrieffer mode due to a subleading superconducting component.
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Affiliation(s)
- Bin Hu
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
| | - Hui Chen
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
- Hefei National Laboratory, 230088, Hefei, Anhui, PR China
| | - Yuhan Ye
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
| | - Zihao Huang
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
| | - Xianghe Han
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
| | - Zhen Zhao
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
| | - Hongqin Xiao
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
| | - Xiao Lin
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
| | - Haitao Yang
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
| | - Ziqiang Wang
- Department of Physics, Boston College, Chestnut Hill, MA, 02467, USA.
| | - Hong-Jun Gao
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China.
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China.
- Hefei National Laboratory, 230088, Hefei, Anhui, PR China.
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Niemann U, Wu YM, Oka R, Hirai D, Wang Y, Suyolcu YE, Kim M, van Aken PA, Takagi H. Crystallization of heavy fermions via epitaxial strain in spinel LiV 2O 4 thin film. Proc Natl Acad Sci U S A 2023; 120:e2215722120. [PMID: 37279264 PMCID: PMC10268588 DOI: 10.1073/pnas.2215722120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Accepted: 04/07/2023] [Indexed: 06/08/2023] Open
Abstract
The mixed-valent spinel LiV2O4 is known as the first oxide heavy-fermion system. There is a general consensus that a subtle interplay of charge, spin, and orbital degrees of freedom of correlated electrons plays a crucial role in the enhancement of quasi-particle mass, but the specific mechanism has remained yet elusive. A charge-ordering (CO) instability of V3+ and V4+ ions that is geometrically frustrated by the V pyrochlore sublattice from forming a long-range CO down to T = 0 K has been proposed as a prime candidate for the mechanism. Here, we uncover the hidden CO instability by applying epitaxial strain on single-crystalline LiV2O4 thin films. We find a crystallization of heavy fermions in a LiV2O4 film on MgO, where a charge-ordered insulator comprising of a stack of V3+ and V4+ layers along [001], the historical Verwey-type ordering, is stabilized by the in-plane tensile and out-of-plane compressive strains from the substrate. Our discovery of the [001] Verwey-type CO, together with previous realizations of a distinct [111] CO, evidence the close proximity of the heavy-fermion state to degenerate CO states mirroring the geometrical frustration of the V pyrochlore lattice, which supports the CO instability scenario for the mechanism behind the heavy-fermion formation.
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Affiliation(s)
- Ulrike Niemann
- Max Planck Institute for Solid State Research,70569Stuttgart, Germany
- Department of Physics, University of Tokyo, Tokyo113-0033, Japan
| | - Yu-Mi Wu
- Max Planck Institute for Solid State Research,70569Stuttgart, Germany
| | - Ryosuke Oka
- Max Planck Institute for Solid State Research,70569Stuttgart, Germany
- Department of Physics, University of Tokyo, Tokyo113-0033, Japan
| | - Daigorou Hirai
- Department of Physics, University of Tokyo, Tokyo113-0033, Japan
| | - Yi Wang
- Max Planck Institute for Solid State Research,70569Stuttgart, Germany
| | - Y. Eren Suyolcu
- Max Planck Institute for Solid State Research,70569Stuttgart, Germany
| | - Minu Kim
- Max Planck Institute for Solid State Research,70569Stuttgart, Germany
| | - Peter A. van Aken
- Max Planck Institute for Solid State Research,70569Stuttgart, Germany
| | - Hidenori Takagi
- Max Planck Institute for Solid State Research,70569Stuttgart, Germany
- Department of Physics, University of Tokyo, Tokyo113-0033, Japan
- Institute for Functional Matter and Quantum Technologies, University of Stuttgart,70550Stuttgart, Germany
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Xue H, Wang L, Wang Z, Zhang G, Peng W, Wu S, Gao CL, An Z, Chen Y, Li W. Fourfold Symmetric Superconductivity in Spinel Oxide LiTi 2O 4(001) Thin Films. ACS NANO 2022; 16:19464-19471. [PMID: 36331279 DOI: 10.1021/acsnano.2c09338] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
The charge frustration with the mixed-valence state inherent to LiTi2O4, which is found to be the only oxide superconductor with spinel structure, is the impetus for paying special attention to unveil the underlying intriguing superconducting properties. Here, we report a pronounced fourfold rotational symmetry of the superconductivity in high-quality single-crystalline LiTi2O4(001) thin films. Both the magnetoresistivity and upper critical field under an applied magnetic field manifest striking fourfold oscillations deep inside the superconducting state, whereas the anisotropy vanishes in the normal state, demonstrating that it is an intrinsic property of the superconducting phase. We attribute this behavior to the unconventional d-wave superconducting Cooper pairs with the irreducible representation of Eg protected by the Oh point group in cubic LiTi2O4. Our findings show the nontrivial character of the pairing interaction in a three-dimensional spinel oxide superconductor.
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Affiliation(s)
| | | | | | | | - Wei Peng
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, and Center for Excellence in Superconducting Electronics, Chinese Academy of Sciences, Shanghai 200050, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
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Nishio K, Ichinokura S, Nakanishi A, Shimizu K, Kobayashi Y, Nakamura N, Imazeki D, Shimizu R, Hirahara T, Watanabe S, Hitosugi T. Ionic Rectification across Ionic and Mixed Conductor Interfaces. NANO LETTERS 2021; 21:10086-10091. [PMID: 34807612 DOI: 10.1021/acs.nanolett.1c03872] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
In electrochemical devices, it is important to control the ionic transport between the electrodes and solid electrolytes. However, it is difficult to tune the transport without applying an electric field. This paper presents a method to modulate the transport via tuning of the electrochemical potential difference by controlling the electronic states at the interfaces. We fabricated thin-film solid-state Li batteries using LiTi2O4 thin films as positive electrodes. The spontaneous Li-ion transport between the solid electrolyte and LiTi2O4 is controlled by tuning the electrochemical potential difference via use of an electrically conducting Nb-doped SrTiO3 substrate. This study establishes the foundation for rectifying the ionic transport via electronic energy band alignment.
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Affiliation(s)
- Kazunori Nishio
- School of Materials and Chemical Technology, Tokyo Institute of Technology, Tokyo 152-8552, Japan
| | - Satoru Ichinokura
- Department of Physics, Tokyo Institute of Technology, Tokyo 152-8550, Japan
| | - Akitaka Nakanishi
- Department of Materials Engineering, The University of Tokyo, Tokyo 113-8656, Japan
| | - Koji Shimizu
- Department of Materials Engineering, The University of Tokyo, Tokyo 113-8656, Japan
| | - Yasutaka Kobayashi
- School of Materials and Chemical Technology, Tokyo Institute of Technology, Tokyo 152-8552, Japan
| | - Naoto Nakamura
- School of Materials and Chemical Technology, Tokyo Institute of Technology, Tokyo 152-8552, Japan
| | - Daisuke Imazeki
- School of Materials and Chemical Technology, Tokyo Institute of Technology, Tokyo 152-8552, Japan
| | - Ryota Shimizu
- School of Materials and Chemical Technology, Tokyo Institute of Technology, Tokyo 152-8552, Japan
| | - Toru Hirahara
- Department of Physics, Tokyo Institute of Technology, Tokyo 152-8550, Japan
| | - Satoshi Watanabe
- Department of Materials Engineering, The University of Tokyo, Tokyo 113-8656, Japan
| | - Taro Hitosugi
- School of Materials and Chemical Technology, Tokyo Institute of Technology, Tokyo 152-8552, Japan
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Boukhvalov DW, Paolucci V, D'Olimpio G, Cantalini C, Politano A. Chemical reactions on surfaces for applications in catalysis, gas sensing, adsorption-assisted desalination and Li-ion batteries: opportunities and challenges for surface science. Phys Chem Chem Phys 2021; 23:7541-7552. [PMID: 32926041 DOI: 10.1039/d0cp03317k] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The study of chemical processes on solid surfaces is a powerful tool to discover novel physicochemical concepts with direct implications for processes based on chemical reactions at surfaces, largely exploited by industry. Recent upgrades of experimental tools and computational capabilities, as well as the advent of two-dimensional materials, have opened new opportunities and challenges for surface science. In this Perspective, we highlight recent advances in application fields strictly connected to novel concepts emerging in surface science. Specifically, we show for selected case-study examples that surface oxidation can be unexpectedly beneficial for improving the efficiency in electrocatalysis (the hydrogen evolution reaction and oxygen evolution reaction) and photocatalysis, as well as in gas sensing. Moreover, we discuss the adsorption-assisted mechanism in membrane distillation for seawater desalination, as well as the use of surface-science tools in the study of Li-ion batteries. In all these applications, surface-science methodologies (both experimental and theoretical) have unveiled new physicochemical processes, whose efficiency can be further tuned by controlling surface phenomena, thus paving the way for a new era for the investigation of surfaces and interfaces of nanomaterials. In addition, we discuss the role of surface scientists in contemporary condensed matter physics, taking as case-study examples specific controversial debates concerning unexpected phenomena emerging in nanosheets of layered materials, solved by adopting a surface-science approach.
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Affiliation(s)
- Danil W Boukhvalov
- College of Science, Institute of Materials Physics and Chemistry, Nanjing Forestry University, Nanjing 210037, P. R. China
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Tada K, Ozaki H, Kiyobayashi T, Kitta M, Tanaka S. How does the Li-distribution in the 16d sites determine the stability of A 3(Li,Ti 5)O 12 (A = Li and Na)? RSC Adv 2020; 10:33509-33516. [PMID: 35515046 PMCID: PMC9056721 DOI: 10.1039/d0ra06125e] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Accepted: 08/28/2020] [Indexed: 12/18/2022] Open
Abstract
Li3(Li,Ti5)O12 (LTO) is a stable and safe negative electrode material for Li-ion batteries, and its Na substitute Na3(Li,Ti5)O12 (NTO) is a counterpart for the Na-ion battery. In LTO and NTO, a sixth of the Ti-sites (16d) in the spinel framework are replaced by Li: Li mixing in the 16d sites. For conducting theoretical studies on these materials, e.g., density functional theory (DFT) calculations, one has to confront the astronomical number of combinations of Li distribution in 16d sites to construct model structures, of which the size is sufficiently large to represent the bulk material properties. Only a limited number of models, whose structures are a priori specified by “researcher intuition,” have been examined thus far, and how Li-mixing determines the material stability has yet to be clarified. Herein, we statistically analyzed the DFT total energy of more than 2 × 104 model structures of LTO and NTO that were extracted from the 4 × 108 possible combinations of Li-mixing with computer-aided symmetry analysis and an automated model building system. The local energy analysis further revealed the local stability/instability of each structure. We found that LTO and NTO stability can be well explained by the apparent coulombic repulsion between Li+ in the 16d sites as if they were placed in a matrix of dielectric constants of 1.92 and 2.04 for LTO and NTO, respectively. That is, the sum of the inverse of the Li–Li distance (S) serves as a good descriptor in predicting the stability of these materials. The extent to which the O2− anions are displaced from the Wyckoff position (32e) is considered to differentiate NTO from LTO. However, the electronic structure of NTO does not significantly differ from that of LTO unless S exceeds a certain limit. These results suggest that the spinel framework tolerates the structural instability and variety to some extent, which is important in constructing a spinel structure with the mixing of other cations, thereby replacing the rare element Li. Li3(Li,Ti5)O12 (LTO) is a stable and safe negative electrode material for Li-ion batteries, and its Na substitute Na3(Li,Ti5)O12 (NTO) is a counterpart for the Na-ion battery.![]()
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Affiliation(s)
- Kohei Tada
- Research Institute of Electrochemical Energy (RIECEN), Department of Energy and Environment, National Institute of Advanced Industrial Science and Technology (AIST) 1-8-31 Midorigaoka Ikeda Osaka 563-8577 Japan
| | - Hiroyuki Ozaki
- Research Institute of Electrochemical Energy (RIECEN), Department of Energy and Environment, National Institute of Advanced Industrial Science and Technology (AIST) 1-8-31 Midorigaoka Ikeda Osaka 563-8577 Japan
| | - Tetsu Kiyobayashi
- Research Institute of Electrochemical Energy (RIECEN), Department of Energy and Environment, National Institute of Advanced Industrial Science and Technology (AIST) 1-8-31 Midorigaoka Ikeda Osaka 563-8577 Japan
| | - Mitsunori Kitta
- Research Institute of Electrochemical Energy (RIECEN), Department of Energy and Environment, National Institute of Advanced Industrial Science and Technology (AIST) 1-8-31 Midorigaoka Ikeda Osaka 563-8577 Japan
| | - Shingo Tanaka
- Research Institute of Electrochemical Energy (RIECEN), Department of Energy and Environment, National Institute of Advanced Industrial Science and Technology (AIST) 1-8-31 Midorigaoka Ikeda Osaka 563-8577 Japan
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Iwaya K, Ohsawa T, Shimizu R, Okada Y, Hitosugi T. Atomic-scale visualization of oxide thin-film surfaces. SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 2018; 19:282-290. [PMID: 29707068 PMCID: PMC5917431 DOI: 10.1080/14686996.2018.1442616] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Revised: 02/15/2018] [Accepted: 02/15/2018] [Indexed: 06/08/2023]
Abstract
The interfaces of complex oxide heterostructures exhibit intriguing phenomena not observed in their constituent materials. The oxide thin-film growth of such heterostructures has been successfully controlled with unit-cell precision; however, atomic-scale understandings of oxide thin-film surfaces and interfaces have remained insufficient. We examined, with atomic precision, the surface and electronic structures of oxide thin films and their growth processes using low-temperature scanning tunneling microscopy. Our results reveal that oxide thin-film surface structures are complicated in contrast to the general perception and that atomically ordered surfaces can be achieved with careful attention to the surface preparation. Such atomically ordered oxide thin-film surfaces offer great opportunities not only for investigating the microscopic origins of interfacial phenomena but also for exploring new surface phenomena and for studying the electronic states of complex oxides that are inaccessible using bulk samples.
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Affiliation(s)
- Katsuya Iwaya
- Advanced Institute for Materials Research (AIMR), Tohoku University, Sendai, Japan
- Center for Emergent Matter Science, RIKEN, Saitama, Japan
| | - Takeo Ohsawa
- Advanced Institute for Materials Research (AIMR), Tohoku University, Sendai, Japan
- National Institute for Materials Research, Ibaraki, Japan
| | - Ryota Shimizu
- Advanced Institute for Materials Research (AIMR), Tohoku University, Sendai, Japan
- School of Materials and Chemical Technology, Tokyo Institute of Technology, Tokyo, Japan
| | - Yoshinori Okada
- Advanced Institute for Materials Research (AIMR), Tohoku University, Sendai, Japan
| | - Taro Hitosugi
- Advanced Institute for Materials Research (AIMR), Tohoku University, Sendai, Japan
- School of Materials and Chemical Technology, Tokyo Institute of Technology, Tokyo, Japan
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Mesoraca S, Knudde S, Leitao DC, Cardoso S, Blamire MG. All-spinel oxide Josephson junctions for high-efficiency spin filtering. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:015804. [PMID: 29135466 DOI: 10.1088/1361-648x/aa9a9d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Obtaining high efficiency spin filtering at room temperature using spinel ferromagnetic tunnel barriers has been hampered by the formation of antiphase boundaries due to their difference in lattice parameters between barrier and electrodes. In this work we demonstrate the use of LiTi2O4 thin films as electrodes in an all-spinel oxide CoFe2O4-based spin filter devices. These structures show nearly perfect epitaxy maintained throughout the structure and so minimise the potential for APBs formation. The LiTi2O4 in these devices is superconducting and so measurements at low temperature have been used to explore details of the tunnelling and Josephson junction behaviour.
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Affiliation(s)
- S Mesoraca
- Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
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