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Narayan DM, Hao P, Kurleto R, Berggren BS, Linn AG, Eckberg C, Saraf P, Collini J, Zavalij P, Hashimoto M, Lu D, Fernandes RM, Paglione J, Dessau DS. Potential Lifshitz transition at optimal substitution in nematic pnictide Ba 1-xSr xNi 2As 2. SCIENCE ADVANCES 2023; 9:eadi4966. [PMID: 37851807 PMCID: PMC10584352 DOI: 10.1126/sciadv.adi4966] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2023] [Accepted: 09/15/2023] [Indexed: 10/20/2023]
Abstract
BaNi2As2 is a structural analog of the pnictide superconductor BaFe2As2, which, like the iron-based superconductors, hosts a variety of ordered phases including charge density waves (CDWs), electronic nematicity, and superconductivity. Upon isovalent Sr substitution on the Ba site, the charge and nematic orders are suppressed, followed by a sixfold enhancement of the superconducting transition temperature (Tc). To understand the mechanisms responsible for enhancement of Tc, we present high-resolution angle-resolved photoemission spectroscopy (ARPES) measurements of the Ba1-xSrxNi2As2 series, which agree well with our density functional theory (DFT) calculations throughout the substitution range. Analysis of our ARPES-validated DFT results indicates a Lifshitz transition and reasonably nested electron and hole Fermi pockets near optimal substitution where Tc is maximum. These nested pockets host Ni dxz/dyz orbital compositions, which we associate with the enhancement of nematic fluctuations, revealing unexpected connections to the iron-pnictide superconductors. This gives credence to a scenario in which nematic fluctuations drive an enhanced Tc.
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Affiliation(s)
- Dushyant M. Narayan
- Center for Experiments on Quantum Materials, Department of Physics, University of Colorado, Boulder, CO 80309, USA
| | - Peipei Hao
- Center for Experiments on Quantum Materials, Department of Physics, University of Colorado, Boulder, CO 80309, USA
| | - Rafał Kurleto
- Center for Experiments on Quantum Materials, Department of Physics, University of Colorado, Boulder, CO 80309, USA
| | - Bryan S. Berggren
- Center for Experiments on Quantum Materials, Department of Physics, University of Colorado, Boulder, CO 80309, USA
| | - A. Garrison Linn
- Center for Experiments on Quantum Materials, Department of Physics, University of Colorado, Boulder, CO 80309, USA
| | - Christopher Eckberg
- Maryland Quantum Materials Center, Department of Physics, University of Maryland, College Park, MD 20742, USA
| | - Prathum Saraf
- Maryland Quantum Materials Center, Department of Physics, University of Maryland, College Park, MD 20742, USA
| | - John Collini
- Maryland Quantum Materials Center, Department of Physics, University of Maryland, College Park, MD 20742, USA
| | - Peter Zavalij
- Department of Chemistry, University of Maryland, College Park, MD 20742, USA
| | - Makoto Hashimoto
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
| | - Donghui Lu
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
| | - Rafael M. Fernandes
- School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA
| | - Johnpierre Paglione
- Maryland Quantum Materials Center, Department of Physics, University of Maryland, College Park, MD 20742, USA
- Canadian Institute for Advanced Research, Toronto, ON M5G-1Z8, Canada
| | - Daniel S. Dessau
- Center for Experiments on Quantum Materials, Department of Physics, University of Colorado, Boulder, CO 80309, USA
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Qin T, Zhong R, Cao W, Shen S, Wen C, Qi Y, Yan S. Real-Space Observation of Unidirectional Charge Density Wave and Complex Structural Modulation in the Pnictide Superconductor Ba 1-xSr xNi 2As 2. NANO LETTERS 2023; 23:2958-2963. [PMID: 37011415 DOI: 10.1021/acs.nanolett.3c00323] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
Here we use low-temperature and variable-temperature scanning tunneling microscopy to study the pnictide superconductor, Ba1-xSrxNi2As2. In the low-temperature phase (triclinic phase) of BaNi2As2, we observe the unidirectional charge density wave (CDW) with Q = 1/3 on both the Ba and NiAs surfaces. On the NiAs surface of the triclinic BaNi2As2, there are structural-modulation-induced chain-like superstructures with distinct periodicities. In the high-temperature phase (tetragonal phase) of BaNi2As2, the NiAs surface appears as the periodic 1 × 2 superstructure. Interestingly, in the triclinic phase of Ba0.5Sr0.5Ni2As2, the unidirectional CDW is suppressed on both the Ba/Sr and NiAs surfaces, and the Sr substitution stabilizes the periodic 1 × 2 superstructure on the NiAs surface, which enhance the superconductivity in Ba0.5Sr0.5Ni2As2. Our results provide important microscopic insights for the interplay among the unidirectional CDW, structural modulation, and superconductivity in this class of pnictide superconductors.
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Affiliation(s)
- Tian Qin
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Ruixia Zhong
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Weizheng Cao
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Shiwei Shen
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Chenhaoping Wen
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Yanpeng Qi
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
- ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai 201210, China
- Shanghai Key Laboratory of High-Resolution Electron Microscopy, ShanghaiTech University, Shanghai 201210, China
| | - Shichao Yan
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
- ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai 201210, China
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Souliou SM, Lacmann T, Heid R, Meingast C, Frachet M, Paolasini L, Haghighirad AA, Merz M, Bosak A, Le Tacon M. Soft-Phonon and Charge-Density-Wave Formation in Nematic BaNi_{2}As_{2}. PHYSICAL REVIEW LETTERS 2022; 129:247602. [PMID: 36563274 DOI: 10.1103/physrevlett.129.247602] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2022] [Revised: 10/14/2022] [Accepted: 11/21/2022] [Indexed: 06/17/2023]
Abstract
We use diffuse and inelastic x-ray scattering to study the formation of an incommensurate charge-density-wave (I-CDW) in BaNi_{2}As_{2}, a candidate system for charge-driven electronic nematicity. Intense diffuse scattering is observed around the modulation vector of the I-CDW, Q_{I-CDW}. It is already visible at room temperature and collapses into superstructure reflections in the long-range ordered state where a small orthorhombic distortion occurs. A clear dip in the dispersion of a low-energy transverse optical phonon mode is observed around Q_{I-CDW}. The phonon continuously softens upon cooling, ultimately driving the transition to the I-CDW state. The transverse character of the soft-phonon branch elucidates the complex pattern of the I-CDW satellites observed in the current and earlier studies and settles the debated unidirectional nature of the I-CDW. The phonon instability and its reciprocal space position are well captured by our ab initio calculations. These, however, indicate that neither Fermi surface nesting, nor enhanced momentum-dependent electron-phonon coupling can account for the I-CDW formation, demonstrating its unconventional nature.
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Affiliation(s)
- S M Souliou
- Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology, D-76021 Karlsruhe, Germany
| | - T Lacmann
- Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology, D-76021 Karlsruhe, Germany
| | - R Heid
- Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology, D-76021 Karlsruhe, Germany
| | - C Meingast
- Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology, D-76021 Karlsruhe, Germany
| | - M Frachet
- Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology, D-76021 Karlsruhe, Germany
| | - L Paolasini
- ESRF The European Synchrotron, 71 avenue des Martyrs, CS 40220 F-38043 Grenoble, Cedex 9, France
| | - A-A Haghighirad
- Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology, D-76021 Karlsruhe, Germany
| | - M Merz
- Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology, D-76021 Karlsruhe, Germany
- Karlsruhe Nano Micro Facility (KNMFi), Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany
| | - A Bosak
- ESRF The European Synchrotron, 71 avenue des Martyrs, CS 40220 F-38043 Grenoble, Cedex 9, France
| | - M Le Tacon
- Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology, D-76021 Karlsruhe, Germany
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Yao Y, Willa R, Lacmann T, Souliou SM, Frachet M, Willa K, Merz M, Weber F, Meingast C, Heid R, Haghighirad AA, Schmalian J, Le Tacon M. An electronic nematic liquid in BaNi 2As 2. Nat Commun 2022; 13:4535. [PMID: 35927267 PMCID: PMC9352674 DOI: 10.1038/s41467-022-32112-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Accepted: 07/14/2022] [Indexed: 11/25/2022] Open
Abstract
Understanding the organizing principles of interacting electrons and the emergence of novel electronic phases is a central endeavor of condensed matter physics. Electronic nematicity, in which the discrete rotational symmetry in the electron fluid is broken while the translational one remains unaffected, is a prominent example of such a phase. It has proven ubiquitous in correlated electron systems, and is of prime importance to understand Fe-based superconductors. Here, we find that fluctuations of such broken symmetry are exceptionally strong over an extended temperature range above phase transitions in \documentclass[12pt]{minimal}
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\begin{document}$${{{{{\rm{Ba}}}}}}{{{{{{\rm{Ni}}}}}}}_{2}{({{{{{{\rm{As}}}}}}}_{1-x}{{{{{{\rm{P}}}}}}}_{x})}_{2}$$\end{document}BaNi2(As1−xPx)2, the nickel homologue to the Fe-based systems. This lends support to a type of electronic nematicity, dynamical in nature, which exhibits a particularly strong coupling to the underlying crystal lattice. Fluctuations between degenerate nematic configurations cause splitting of phonon lines, without lifting degeneracies nor breaking symmetries, akin to spin liquids in magnetic systems. Electronic nematicity is typically associated with the breaking of rotational symmetry. Here the authors report unusual nematicity in BaNi2As2, manifested in a large splitting of the optical phonon mode above the structural transition temperature, and link it to the coupling between the lattice and nematic fluctuations.
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Affiliation(s)
- Yi Yao
- Institut für Quantenmaterialien und -technologien, Karlsruher Institut für Technologie, 76021, Karlsruhe, Germany
| | - Roland Willa
- Institut für Theorie der Kondensierten Materie, Karlsruher Institut für Technologie, 76131, Karlsruhe, Germany
| | - Tom Lacmann
- Institut für Quantenmaterialien und -technologien, Karlsruher Institut für Technologie, 76021, Karlsruhe, Germany
| | - Sofia-Michaela Souliou
- Institut für Quantenmaterialien und -technologien, Karlsruher Institut für Technologie, 76021, Karlsruhe, Germany
| | - Mehdi Frachet
- Institut für Quantenmaterialien und -technologien, Karlsruher Institut für Technologie, 76021, Karlsruhe, Germany
| | - Kristin Willa
- Institut für Quantenmaterialien und -technologien, Karlsruher Institut für Technologie, 76021, Karlsruhe, Germany
| | - Michael Merz
- Institut für Quantenmaterialien und -technologien, Karlsruher Institut für Technologie, 76021, Karlsruhe, Germany.,Karlsruhe Nano Micro Facility (KNMFi), Karlsruhe Institute of Technology (KIT), 76344, Eggenstein-Leopoldshafen, Germany
| | - Frank Weber
- Institut für Quantenmaterialien und -technologien, Karlsruher Institut für Technologie, 76021, Karlsruhe, Germany
| | - Christoph Meingast
- Institut für Quantenmaterialien und -technologien, Karlsruher Institut für Technologie, 76021, Karlsruhe, Germany
| | - Rolf Heid
- Institut für Quantenmaterialien und -technologien, Karlsruher Institut für Technologie, 76021, Karlsruhe, Germany
| | - Amir-Abbas Haghighirad
- Institut für Quantenmaterialien und -technologien, Karlsruher Institut für Technologie, 76021, Karlsruhe, Germany
| | - Jörg Schmalian
- Institut für Quantenmaterialien und -technologien, Karlsruher Institut für Technologie, 76021, Karlsruhe, Germany.,Institut für Theorie der Kondensierten Materie, Karlsruher Institut für Technologie, 76131, Karlsruhe, Germany
| | - Matthieu Le Tacon
- Institut für Quantenmaterialien und -technologien, Karlsruher Institut für Technologie, 76021, Karlsruhe, Germany.
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