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Storeck G, Horstmann JG, Diekmann T, Vogelgesang S, von Witte G, Yalunin SV, Rossnagel K, Ropers C. Structural dynamics of incommensurate charge-density waves tracked by ultrafast low-energy electron diffraction. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2020; 7:034304. [PMID: 32596414 PMCID: PMC7311179 DOI: 10.1063/4.0000018] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Accepted: 04/13/2020] [Indexed: 06/11/2023]
Abstract
We study the non-equilibrium structural dynamics of the incommensurate and nearly commensurate charge-density wave (CDW) phases in 1T-TaS 2 . Employing ultrafast low-energy electron diffraction with 1 ps temporal resolution, we investigate the ultrafast quench and recovery of the CDW-coupled periodic lattice distortion (PLD). Sequential structural relaxation processes are observed by tracking the intensities of main lattice as well as satellite diffraction peaks and the diffuse scattering background. Comparing distinct groups of diffraction peaks, we disentangle the ultrafast quench of the PLD amplitude from phonon-related reductions of the diffraction intensity. Fluence-dependent relaxation cycles reveal a long-lived partial suppression of the order parameter for up to 60 ps, far outlasting the initial amplitude recovery and electron-phonon scattering times. This delayed return to a quasi-thermal level is controlled by lattice thermalization and coincides with the population of zone-center acoustic modes, as evidenced by a structured diffuse background. The long-lived non-equilibrium order parameter suppression suggests hot populations of CDW-coupled lattice modes. Finally, a broadening of the superlattice peaks is observed at high fluences, pointing to a non-linear generation of phase fluctuations.
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Affiliation(s)
- G. Storeck
- 4th Physical Institute, Solids and Nanostructures, University of Göttingen, 37077 Göttingen, Germany
| | - J. G. Horstmann
- 4th Physical Institute, Solids and Nanostructures, University of Göttingen, 37077 Göttingen, Germany
| | - T. Diekmann
- 4th Physical Institute, Solids and Nanostructures, University of Göttingen, 37077 Göttingen, Germany
| | - S. Vogelgesang
- 4th Physical Institute, Solids and Nanostructures, University of Göttingen, 37077 Göttingen, Germany
| | - G. von Witte
- 4th Physical Institute, Solids and Nanostructures, University of Göttingen, 37077 Göttingen, Germany
| | - S. V. Yalunin
- 4th Physical Institute, Solids and Nanostructures, University of Göttingen, 37077 Göttingen, Germany
| | | | - C. Ropers
- Author to whom correspondence should be addressed:
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Zhang J, Lian C, Guan M, Ma W, Fu H, Guo H, Meng S. Photoexcitation Induced Quantum Dynamics of Charge Density Wave and Emergence of a Collective Mode in 1 T-TaS 2. NANO LETTERS 2019; 19:6027-6034. [PMID: 31416307 DOI: 10.1021/acs.nanolett.9b01865] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Photoexcitation is a powerful means in distinguishing different interactions and manipulating the states of matter, especially in charge density wave (CDW) materials. The CDW state of 1T-TaS2 has been widely studied experimentally mainly because of its intriguing laser-induced ultrafast responses of electronic and lattice subsystems. However, the microscopic atomic dynamics and underlying electronic mechanism upon photoexcitation remain unclear. Here, we demonstrate photoexcitation induced ultrafast dynamics of CDW in 1T-TaS2 using time-dependent density functional theory molecular dynamics. We discover a novel collective oscillation mode between the CDW state and a transient state induced by photodoping, which is significantly different from thermally induced phonon mode and attributed to the modification of the potential energy surface from laser excitation. In addition, our finding validates nonthermal melting of CDW induced at low light intensities, supporting that conventional hot electron model is inadequate to explain photoinduced dynamics. Our results provide a deep insight into the coherent electron and lattice quantum dynamics during the formation and excitation of CDW in 1T-TaS2.
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Affiliation(s)
- Jin Zhang
- Beijing National Laboratory for Condensed Matter Physics , Institute of Physics, Chinese Academy of Sciences , Beijing 100190 , P. R. China
- School of Physical Sciences , University of Chinese Academy of Sciences , Beijing 100049 , P. R. China
| | - Chao Lian
- Beijing National Laboratory for Condensed Matter Physics , Institute of Physics, Chinese Academy of Sciences , Beijing 100190 , P. R. China
| | - Mengxue Guan
- Beijing National Laboratory for Condensed Matter Physics , Institute of Physics, Chinese Academy of Sciences , Beijing 100190 , P. R. China
- School of Physical Sciences , University of Chinese Academy of Sciences , Beijing 100049 , P. R. China
| | - Wei Ma
- Beijing National Laboratory for Condensed Matter Physics , Institute of Physics, Chinese Academy of Sciences , Beijing 100190 , P. R. China
- School of Physical Sciences , University of Chinese Academy of Sciences , Beijing 100049 , P. R. China
| | - Huixia Fu
- Beijing National Laboratory for Condensed Matter Physics , Institute of Physics, Chinese Academy of Sciences , Beijing 100190 , P. R. China
- School of Physical Sciences , University of Chinese Academy of Sciences , Beijing 100049 , P. R. China
| | - Haizhong Guo
- School of Physics and Engineering , Zhengzhou University , Zhengzhou , Henan 450001 , P. R. China
| | - Sheng Meng
- Beijing National Laboratory for Condensed Matter Physics , Institute of Physics, Chinese Academy of Sciences , Beijing 100190 , P. R. China
- School of Physical Sciences , University of Chinese Academy of Sciences , Beijing 100049 , P. R. China
- Songshan Lake Materials Laboratory , Dongguan , Guangdong 523808 , P. R. China
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