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Haque SRU, Michael MH, Zhu J, Zhang Y, Windgätter L, Latini S, Wakefield JP, Zhang GF, Zhang J, Rubio A, Checkelsky JG, Demler E, Averitt RD. Terahertz parametric amplification as a reporter of exciton condensate dynamics. Nat Mater 2024:10.1038/s41563-023-01755-2. [PMID: 38172546 DOI: 10.1038/s41563-023-01755-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2022] [Accepted: 11/06/2023] [Indexed: 01/05/2024]
Abstract
Condensates are a hallmark of emergence in quantum materials such as superconductors and charge density waves. Excitonic insulators are an intriguing addition to this library, exhibiting spontaneous condensation of electron-hole pairs. However, condensate observables can be obscured through parasitic coupling to the lattice. Here we employ nonlinear terahertz spectroscopy to disentangle such obscurants through measurement of the quantum dynamics. We target Ta2NiSe5, a putative room-temperature excitonic insulator in which electron-lattice coupling dominates the structural transition (Tc = 326 K), hindering identification of excitonic correlations. A pronounced increase in the terahertz reflectivity manifests following photoexcitation and exhibits a Bose-Einstein condensation-like temperature dependence well below the Tc, suggesting an approach to monitor the exciton condensate dynamics. Nonetheless, dynamic condensate-phonon coupling remains as evidenced by peaks in the enhanced reflectivity spectrum at select infrared-active phonon frequencies, indicating that parametric reflectivity enhancement arises from phonon squeezing. Our results highlight that coherent dynamics can drive parametric stimulated emission.
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Affiliation(s)
- Sheikh Rubaiat Ul Haque
- Department of Physics, University of California San Diego, La Jolla, CA, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
| | | | - Junbo Zhu
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Yuan Zhang
- Department of Physics, University of California San Diego, La Jolla, CA, USA
| | - Lukas Windgätter
- Max Planck Institute for the Structure and Dynamics of Matter (MPSD), Hamburg, Germany
| | - Simone Latini
- Max Planck Institute for the Structure and Dynamics of Matter (MPSD), Hamburg, Germany
| | - Joshua P Wakefield
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Gu-Feng Zhang
- Department of Physics, University of California San Diego, La Jolla, CA, USA
| | - Jingdi Zhang
- Department of Physics, University of California San Diego, La Jolla, CA, USA
- Department of Physics, The Hong Kong University of Science and Technology, Hongkong, China
| | - Angel Rubio
- Max Planck Institute for the Structure and Dynamics of Matter (MPSD), Hamburg, Germany
- Center for Computational Quantum Physics, The Flatiron Institute, New York, NY, USA
| | - Joseph G Checkelsky
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Eugene Demler
- Department of Physics, Harvard University, Cambridge, MA, USA
- Institute for Theoretical Physics, ETH Zürich, Zürich, Switzerland
| | - Richard D Averitt
- Department of Physics, University of California San Diego, La Jolla, CA, USA.
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Mazza G, Rösner M, Windgätter L, Latini S, Hübener H, Millis AJ, Rubio A, Georges A. Nature of Symmetry Breaking at the Excitonic Insulator Transition: Ta_{2}NiSe_{5}. Phys Rev Lett 2020; 124:197601. [PMID: 32469559 DOI: 10.1103/physrevlett.124.197601] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Accepted: 04/23/2020] [Indexed: 06/11/2023]
Abstract
Ta_{2}NiSe_{5} is one of the most promising materials for hosting an excitonic insulator ground state. While a number of experimental observations have been interpreted in this way, the precise nature of the symmetry breaking occurring in Ta_{2}NiSe_{5}, the electronic order parameter, and a realistic microscopic description of the transition mechanism are, however, missing. By a symmetry analysis based on first-principles calculations, we uncover the discrete lattice symmetries which are broken at the transition. We identify a purely electronic order parameter of excitonic nature that breaks these discrete crystal symmetries and contributes to the experimentally observed lattice distortion from an orthorombic to a monoclinic phase. Our results provide a theoretical framework to understand and analyze the excitonic transition in Ta_{2}NiSe_{5} and settle the fundamental questions about symmetry breaking governing the spontaneous formation of excitonic insulating phases in solid-state materials.
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Affiliation(s)
- Giacomo Mazza
- Department of Quantum Matter Physics, University of Geneva, Quai Ernest-Ansermet 24, 1211 Geneva, Switzerland
- CPHT, CNRS, Ecole Polytechnique, IP Paris, F-91128 Palaiseau, France
- Collège de France, 11 place Marcelin Berthelot, 75005 Paris, France
| | - Malte Rösner
- Radboud University, Institute for Molecules and Materials, Heijendaalseweg 135, 6525 AJ Nijmegen, Netherlands
| | - Lukas Windgätter
- Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Simone Latini
- Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Hannes Hübener
- Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Andrew J Millis
- Center for Computational Quantum Physics, Flatiron Institute, New York, New York 10010, USA
- Department of Physics, Columbia University, New York, New York 10027, USA
| | - Angel Rubio
- Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
- Center for Computational Quantum Physics, Flatiron Institute, New York, New York 10010, USA
- Nano-Bio Spectroscopy Group, Departamento de Física de Materiales, Universidad del País Vasco, 20018 San Sebastian, Spain
| | - Antoine Georges
- Department of Quantum Matter Physics, University of Geneva, Quai Ernest-Ansermet 24, 1211 Geneva, Switzerland
- CPHT, CNRS, Ecole Polytechnique, IP Paris, F-91128 Palaiseau, France
- Collège de France, 11 place Marcelin Berthelot, 75005 Paris, France
- Center for Computational Quantum Physics, Flatiron Institute, New York, New York 10010, USA
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