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Liu WH, Gu YX, Wang Z, Li SS, Wang LW, Luo JW. Origin of Immediate Damping of Coherent Oscillations in Photoinduced Charge-Density-Wave Transition. PHYSICAL REVIEW LETTERS 2023; 130:146901. [PMID: 37084436 DOI: 10.1103/physrevlett.130.146901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Revised: 02/16/2023] [Accepted: 03/13/2023] [Indexed: 05/03/2023]
Abstract
In stark contrast to the conventional charge density wave (CDW) materials, the one-dimensional CDW on the In/Si(111) surface exhibits immediate damping of the CDW oscillation during the photoinduced phase transition. Here, we successfully reproduce the experimental observation of the photoinduced CDW transition on the In/Si(111) surface by performing real-time time-dependent density functional theory (rt-TDDFT) simulations. We show that photoexcitation promotes valence electrons from the Si substrate to the empty surface bands composed primarily of the covalent p-p bonding states of the long In-In bonds. Such photoexcitation generates interatomic forces to shorten the long In-In bonds and thus drives the structural transition. After the structural transition, these surface bands undergo a switch among different In-In bonds, causing a rotation of the interatomic forces by about π/6 and thus quickly damping the oscillations in feature CDW modes. These findings provide a deeper understanding of photoinduced phase transitions.
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Affiliation(s)
- Wen-Hao Liu
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yu-Xiang Gu
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Zhi Wang
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
| | - Shu-Shen Li
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Lin-Wang Wang
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
| | - Jun-Wei Luo
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
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Hafke B, Witte T, Janoschka D, Dreher P, Meyer zu Heringdorf FJ, Horn-von Hoegen M. Condensation of ground state from a supercooled phase in the Si(111)-(4 × 1) → (8 × 2)-indium atomic wire system. Struct Dyn 2019; 6:045101. [PMID: 31406702 PMCID: PMC6677565 DOI: 10.1063/1.5111636] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Accepted: 07/18/2019] [Indexed: 11/14/2022] Open
Abstract
Strong optical irradiation of indium atomic wires on a Si(111) surface causes the nonthermal structural transition from the (8 × 2) reconstructed ground state to an excited (4 × 1) state. The immediate recovery of the system to the ground state is hindered by an energy barrier for the collective motion of the indium atoms along the reaction coordinate from the (4 × 1) to the (8 × 2) state. This metastable, supercooled state can only recover through nucleation of the ground state at defects like adsorbates or step edges. Subsequently, a recovery front propagates with constant velocity across the surface and the (8 × 2) ground state is reinstated. In a combined femtosecond electron diffraction and photoelectron emission microscopy study, we determined—based on the step morphology—a velocity of this recovery front of ∼100 m/s.
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Affiliation(s)
- B. Hafke
- Department of Physics and CENIDE, University Duisburg-Essen,
Lotharstr. 1, 47057 Duisburg, Germany
| | - T. Witte
- Department of Physics and CENIDE, University Duisburg-Essen,
Lotharstr. 1, 47057 Duisburg, Germany
| | - D. Janoschka
- Department of Physics and CENIDE, University Duisburg-Essen,
Lotharstr. 1, 47057 Duisburg, Germany
| | - P. Dreher
- Department of Physics and CENIDE, University Duisburg-Essen,
Lotharstr. 1, 47057 Duisburg, Germany
| | | | - M. Horn-von Hoegen
- Department of Physics and CENIDE, University Duisburg-Essen,
Lotharstr. 1, 47057 Duisburg, Germany
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Hafke B, Witte T, Brand C, Duden T, Horn-von Hoegen M. Pulsed electron gun for electron diffraction at surfaces with femtosecond temporal resolution and high coherence length. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2019; 90:045119. [PMID: 31042971 DOI: 10.1063/1.5086124] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Accepted: 03/20/2019] [Indexed: 06/09/2023]
Abstract
We present a newly designed 30 kV pulsed electron gun for ultrafast electron diffraction suited for pump-probe setups driven by femtosecond laser pulses. The electron gun can be operated both in transmission and reflection geometry. A robust design with a back illuminated Au photocathode, extraction fields of 7.5 kV/mm, and a magnetic focus lens ensures reliable daily use. Magnetic deflectors allow for beam alignment and characterization. Focusing of the UV pulse on the photocathode results in a small source size of photoemitted electrons and thus a high transverse coherence length of more than 50 nm in diffraction. A low difference of ΔE = 0.1 eV between the work function of the 10 nm Au photocathode and photon energy of the frequency tripled UV laser pulses results in an instrumental temporal resolution of 330 fs full width at half maximum. This resolution is discussed with respect to the number of electrons per pulse.
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Affiliation(s)
- B Hafke
- Department of Physics and Center for Nanointegration CENIDE, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
| | - T Witte
- Department of Physics and Center for Nanointegration CENIDE, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
| | - C Brand
- Department of Physics and Center for Nanointegration CENIDE, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
| | - Th Duden
- Th. Duden Konstruktionsbüro, Borgsen-Allee 35, 33649 Bielefeld, Germany
| | - M Horn-von Hoegen
- Department of Physics and Center for Nanointegration CENIDE, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
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