Abstract
Monolayer transition metal dichalcogenides (TMDs), an emerging family of two-dimensional (2D) semiconductors with a direct bandgap at visible and near-infrared range, have been intriguing great interests for their extraordinary optical and electronic properties, such as enhanced exciton effect, valley related physics, giant spin-obit coupling and spin-valley locking. In this seminar, optical and electrical characterization of 2D TMDs focusing on the study of exciton binding energy and the optical control of spin-polarized photocurrents of 2D TMDs will be discussed.
The exciton binding energy in monolayer WS2 was measured to be 0.71 eV in our experiments. This was directly extracted as the energy difference between the single particle bandgap obtained by two-photon photoluminescence excitation (TP-PLE) spectroscopy and the optical bandgap obtained by linear absorption and photoluminescence (PL) spectroscopy.
Spin-polarized photocurrents were generated by circularly polarized laser and electrically detected by the spin-valve-like device. Remarkably, spin polarization of the photocurrents was shown to be manipulated by tuning photon energy of the circularly polarized excitation light with the same helicity, utilizing the valley dependent optical selection rules, the giant spin-orbit coupling and the spin-valley locking in monolayer TMDs.
Anyone interested is welcome to attend.