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arXiv · 1405.5141

Temperature Dependent Valley Relaxation Dynamics in Single Layer WS2 Measured Using Ultrafast Spectroscopy

Cong Mai·Yuriy G. Semenov·Andrew Barrette·Yifei Yu·Zhenghe Jin·Linyou Cao·Ki Wook Kim·Kenan Gundogdu
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Abstract

We measured the lifetime of optically created valley polarization in single layer WS2 using transient absorption spectroscopy. The electron valley relaxation is very short (< 1ps). 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 spin degenerate Gamma valley. This second process is thermally activated with an Arrhenius behavior due to the energy barrier between Gamma and K valleys.

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Cong Mai, Yuriy G. Semenov, Andrew Barrette, Yifei Yu, Zhenghe Jin, Linyou Cao, Ki Wook Kim, Kenan Gundogdu. 2014-05-20. Temperature Dependent Valley Relaxation Dynamics in Single Layer WS2 Measured Using Ultrafast Spectroscopy. https://doi.org/10.1103/physrevb.90.041414

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