Ab initio approaches to Resonant Raman Spectroscopy of Transition Metal Dichalcogenides
English
Pereira Coutada Miranda, Henrique[University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit >]
22-Sep-2017
University of Luxembourg, Luxembourg, Luxembourg
[en] This thesis deals with the theory and simulation of resonant Raman spectroscopy in two-dimensional transition metal dichalcogenides. We present two different ab initio approaches. In the first, we calculate the Raman susceptibility tensor as a function of laser energy from the change of the dielectric susceptibility with atomic displacements. In the second, we formulate the Raman tensor in terms of time-dependent perturbation theory and calculate it using electron-light and electron-phonon coupling matrix elements obtained from density functional theory. We investigate the role of resonance, quantum interference and excitonic effects in the Raman spectra of single and triple-layer MoTe2. We compare our simulations with experimental results, explaining the dependence of the Raman intensities on the excitation energy. We demonstrate that the two approaches are formally and numerically equivalent in the adiabatic limit. In addition, the second approach allows to include the dynamical effects and captures a shift of the intensities with respect to the adiabatic case. This method is also more computationally efficient and is extended to include temperature effects using many-body perturbation theory. We have implemented both of these methods in a software package with interfaces to open source ab initio codes. Furthermore, we have developed web based tools to visualize excitonic states and phonon modes.
Fonds National de la Recherche - FnR
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[University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit >]
