Ultrafast non-radiative dynamics of atomically thin MoSe2
- SLAC National Accelerator Lab., Menlo Park, CA (United States). Linac Coherent Light Source (LCLS), Stanford PULSE Inst.
- Rice Univ., Houston, TX (United States). Dept. of Materials Science and NanoEngineering
- Univ. of Southern California, Los Angeles, CA (United States). Collaboratory for Advanced Computing and Simulations
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- Kumamoto Univ. (Japan). Dept. of Physics
- SLAC National Accelerator Lab., Menlo Park, CA (United States). Linac Coherent Light Source (LCLS)
- SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford PULSE Inst.
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, MoSe2. 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 carrier 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 MoSe2 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.
- Research Organization:
- SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)
- Grant/Contract Number:
- AC02-76SF00515; SC00014607; AC02-05CH11231; ACI-1548562
- OSTI ID:
- 1399583
- Journal Information:
- Nature Communications, Vol. 8, Issue 1; ISSN 2041-1723
- Publisher:
- Nature Publishing GroupCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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