Dresden 2017 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 6: Focus Session: Two-Dimensional Materials I (joint session DS, HL, TT, organized by HL)

TT 6.7: Talk

Monday, March 20, 2017, 12:00–12:15, POT 81

Carrier dynamics in MoS2 — •Michael Lorke, A. Steinhoff, M. Florian, C. Gies, M. Roesner, T. Wehling, and F. Jahnke — Institute for Theoretical Physics, University of Bremen, Germany

In the context of the current interest in transition-metal dichalcogenides, we study the optical generation and relaxation of excited carriers and their influence on optical properties. In these two-dimensional atomically thin semiconductors, the Coulomb interaction is known to be much stronger than in quantum wells of conventional semiconductors like GaAs, as witnessed by the up to 50 times larger exciton binding energy. The question arises, whether this translates into equivalently faster carrier-carrier Coulomb scattering of excited carriers. We answer this question by combining ab-initio band-structures and single-particle wave functions with kinetic equations for the Coulomb-induced carrier scattering in the full Brillouin zone, We find an ultrafast redistrubution of carriers into different valleys of the band structure on a 100fs timescale. The other main source of carrier relaxation is the interaction of the excited carriers with phonons. To analyze carrier-phonon scattering and dephasing, we solve kinetic equations, based on ab-initio carrier-phonon interaction matrix elements, both for carriers and phonons, including heating effects due to the excitation of non-equilibrium phonons. We find that within 100fs the electrons have relaxed into the valleys of the bandstructure, demostrating fast carrier dynamics, which is accompanied by the generation of non-equilibrium phonons. This process is followed by carrier cooling on a timescale of about 1ps, which is consistent with recent experimental findings.