title: Trion fine structure and coupled spin-valley dynamics in monolayer tungsten disulfide.
abstract: Monolayer transition-metal dichalcogenides have recently emerged as possible candidates for valleytronic applications, as the spin and valley pseudospin are directly coupled and stabilized by a large spin splitting. The optical properties of these two-dimensional crystals are dominated by tightly bound electron-hole pairs (excitons) and more complex quasiparticles such as charged excitons (trions). Here we investigate monolayer WS2 samples via photoluminescence and time-resolved Kerr rotation. In photoluminescence and in energy-dependent Kerr rotation measurements, we are able to resolve two different trion states, which we interpret as intravalley and intervalley trions. Using time-resolved Kerr rotation, we observe a rapid initial valley polarization decay for the A exciton and the trion states. Subsequently, we observe a crossover towards exciton-exciton interaction-related dynamics, consistent with the formation and decay of optically dark A excitons. By contrast, resonant excitation of the B exciton transition leads to a very slow decay of the Kerr signal.
authors: Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93040 Regensburg, Germany.
authors: Gerd
authors: G
authors: Plechinger
authors: Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93040 Regensburg, Germany.
authors: Philipp
authors: P
authors: Nagler
authors: Physikalisches Institut, Westfälische Wilhelms-Universität Münster, D-48149 Münster, Germany.
authors: Ashish
authors: A
authors: Arora
authors: Physikalisches Institut, Westfälische Wilhelms-Universität Münster, D-48149 Münster, Germany.
authors: Robert
authors: R
authors: Schmidt
authors: Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93040 Regensburg, Germany.
authors: Alexey
authors: A
authors: Chernikov
authors: High Field Magnet Laboratory (HFML-EMFL), Radboud University, 6525 ED Nijmegen, The Netherlands.
authors: Andrés Granados
authors: AG
authors: Del Águila
authors: High Field Magnet Laboratory (HFML-EMFL), Radboud University, 6525 ED Nijmegen, The Netherlands.
authors: Peter C M
authors: PC
authors: Christianen
authors: Physikalisches Institut, Westfälische Wilhelms-Universität Münster, D-48149 Münster, Germany.
authors: Rudolf
authors: R
authors: Bratschitsch
authors: Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93040 Regensburg, Germany.
authors: Christian
authors: C
authors: Schüller
authors: Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93040 Regensburg, Germany.
authors: Tobias
authors: T
authors: Korn