Exciton valley relaxation in a single layer of WS2 measured by ultrafast spectroscopy

作     者：Cong Mai Yuriy G. Semenov Andrew Barrette Yifei Yu Zhenghe Jin Linyou Cao Ki Wook Kim Kenan Gundogdu 

作者机构：Department of Physics North Carolina State University Raleigh North Carolina 27695 USA Department of Electrical and Computer Engineering North Carolina State University Raleigh North Carolina 27695 USA Department of Material Science and Engineering North Carolina State University Raleigh North Carolina 27695 USA 

出 版 物：《Physical Review B》 (Phys. Rev. B Condens. Matter Mater. Phys.)

年 卷 期：2014年第90卷第4期

页      面：041414(R)-041414(R)页

核心收录：

学科分类：07[理学] 0702[理学-物理学] 

基　　金：Army Research Office  (W911NF-13-1-0201) 

主　　题：SPECTRUM analysis SPIN polarization ACTIVATION energy EXCITON theory ABSORPTION spectra 

摘      要：We measured the lifetime of optically created valley polarization in single-layer WS2 using transient absorption spectroscopy. The electron valley relaxation is very short (1 ps). However, the hole valley lifetime is at least two orders of magnitude longer and exhibits a temperature dependence that cannot be explained by single-carrier spin/valley relaxation mechanisms. Our theoretical analysis suggests that a collective contribution of two potential processes may explain the valley relaxation in single-layer WS2. One process involves direct scattering of excitons from K to K′ valleys with a spin flip-flop interaction. The other mechanism involves scattering through the spin-degenerate Γ valley. This second process is thermally activated with an Arrhenius behavior due to the energy barrier between the Γ and K valleys.