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Title: Ultrafast non-radiative dynamics of atomically thin MoSe 2

Non-radiative energy dissipation in photoexcited materials and resulting atomic dynamics provide a promising pathway to induce structural phase transitions in two-dimensional materials. However, these dynamics have not been explored in detail thus far because of incomplete understanding of interaction between the electronic and atomic degrees of freedom, and a lack of direct experimental methods to quantify real-time atomic motion and lattice temperature. Here, we explore the ultrafast conversion of photoenergy to lattice vibrations in a model bi-layered semiconductor, molybdenum diselenide, MoSe 2. Specifically, we characterize sub-picosecond lattice dynamics initiated by the optical excitation of electronic charge carriers in the high electron-hole plasma density regime. Our results focuses on the first ten picosecond dynamics subsequent to photoexcitation before the onset of heat transfer to the substrate, which occurs on a ~100 picosecond time scale. Photoinduced atomic motion is probed by measuring the time dependent Bragg diffraction of a delayed mega-electronvolt femtosecond electron beam. Transient lattice temperatures are characterized through measurement of Bragg peak intensities and calculation of the Debye-Waller factor (DWF). These measurements show a sub-picosecond decay of Bragg diffraction and a correspondingly rapid rise in lattice temperatures. We estimate a high quantum yield for the conversion of excited charge carriermore » energy to lattice motion under our experimental conditions, indicative of a strong electron-phonon interaction. First principles nonadiabatic quantum molecular dynamics simulations (NAQMD) on electronically excited MoSe 2 bilayers reproduce the observed picosecond-scale increase in lattice temperature and ultrafast conversion of photoenergy to lattice vibrations. Calculation of excited-state phonon dispersion curves suggests that softened vibrational modes in the excited state are involved in efficient and rapid energy transfer between the electronic system and the lattice.« less
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [1] ;  [4] ;  [2] ;  [2] ;  [2] ;  [4] ;  [4] ;  [3] ;  [2] ;  [3] ;  [3] ;  [5] ;  [4] ;  [6] ;  [7]
  1. SLAC National Accelerator Lab., Menlo Park, CA (United States). Linac Coherent Light Source (LCLS), Stanford PULSE Inst.
  2. Rice Univ., Houston, TX (United States). Dept. of Materials Science and NanoEngineering
  3. Univ. of Southern California, Los Angeles, CA (United States). Collaboratory for Advanced Computing and Simulations
  4. SLAC National Accelerator Lab., Menlo Park, CA (United States)
  5. Kumamoto Univ. (Japan). Dept. of Physics
  6. SLAC National Accelerator Lab., Menlo Park, CA (United States). Linac Coherent Light Source (LCLS)
  7. SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford PULSE Inst.
Publication Date:
Grant/Contract Number:
AC02-76SF00515; SC00014607; AC02-05CH11231; ACI-1548562
Type:
Accepted Manuscript
Journal Name:
Nature Communications
Additional Journal Information:
Journal Volume: 8; Journal Issue: 1; Journal ID: ISSN 2041-1723
Publisher:
Nature Publishing Group
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE
OSTI Identifier:
1399583