講演情報
[17p-K102-1][The 57th Young Scientist Presentation Award Speech] Control of the valley lifetime in a suspended WSe2 monolayer by opto-electro-mechanical tuning
〇Giacomo Mariani1, Yoji Kunihashi1, Louis Smet1, Taro Wakamura1, Satoshi Sasaki1, Jun Ishihara2, Makoto Kohda2, Junsaku Nitta1,2, Haruki Sanada1 (1.NTT-BRL, 2.Tohoku Univ.)
キーワード：
2D materials、Transition-metal dichalcogenides、Kerr rotation
Two-dimensional (2D) transition-metal dichalcogenides (TMD) are emerging materials which exhibit novel physical phenomena related to their valley degree of freedom. However, contact with other materials degrades the properties of 2D TMD; monolayers suspended over empty spaces are an alternative. The contact-free nature of suspended TMD monolayers enables a precise control of the intrinsic valley lifetime. Here, we report that the lifetime of the valley polarization can be controlled by tuning the optical, electrical, and mechanical properties of a suspended and undoped WSe2 monolayer. In previous studies related to suspended monolayers, photoluminescence spectroscopy was used to probe bright and short-lived exciton dynamics as a function of the monolayer deflection produced by electrostatic gating. However, since photoluminescence gives only a limited overview of the carrier dynamics, it does not reveal the contribution of neither “resident” carriers nor non-radiative excitonic species which are expected to have valley lifetimes on the order of nano- and micro-seconds. In our study, we measured the valley polarization of a suspended monolayer by using a two-color and time-resolved Kerr rotation spectroscopy which allowed us to discuss the long lifetime of the valley polarization given by charged resident carriers as a function of a gate voltage applied to the device. Moreover, we strategically designed the mechanical, optical, and electrical parameters of our device to optimize the signal-to-noise ratio of the Kerr rotation spectroscopy conducted at a temperature of 7 K. As a result, we realized the control of the valley lifetime in range of 1-100 ns by electrostatic gating in a low doping and strain regime of the material. As a next step after these experiments, we have further improved our fabrication techniques to reduce the influence of other factors such as lattice defects or strain puddles on the intrinsic carrier dynamics in suspended monolayers.