Electrical Valley Filtering in Transition Metal Dichalcogenides
Tzu-Chi Hsieh1*, Mei-Yin Chou1,2,3, Yu-Shu Wu4,5
1Institute of Atomic and Molecular Science, Academia Sinica, Taipei, Taiwan
2School of Physics, Georgia Institute of Technology, Georgia, USA
3Department of Physics, National Taiwan University, Taipei, Taiwan
4Department of Electrical Engineering, National Tsing-Hua University, Hsinchu, Taiwan
5Department of Physics, National Tsing-Hua University, Hsinchu, Taiwan
* presenting author:Tzu-Chi Hsieh, email:zihcisie@gmail.com
Electrons in transition metal dichalcogenides (TMDs) possess the novel degree of freedom known as valley pseudopsin. Due to the unique spin-valley coupling, spins and valleys of electrons are both well protected in these materials, making TMDs good candidates for the implementation of spin-valleytronics. Following our previous proposal of valleytronics in gapped graphene systems [1,2,3], the valley-orbit interaction (VOI) is considered here as a potential mechanism to implement all-electrical spin-valleytronics. We propose a scheme utilizing a potential barrier to produce valley-dependent tunneling probabilities and generate valley-polarized currents. Based on tight-binding models, we study the hole transmission through a potential barrier in zigzag or armchair directions as functions of incident energy and angle. It is found that both VOI and band structure warping contribute to valley-dependent tunneling, with the VOI contribution being manifest only for asymmetric potentials but vanishing for symmetric potentials, and the warping contribution reaching maximum for transmission in the armchair direction. It is demonstrated that the valley polarization can be enhanced when potential barriers are increased in width or height. Specifically, for transmission ~ 0.1 our numerical result shows that valley-polarization of a few percents can be achieved.

[1] G. Y. Wu, N.-Y. Lue, and L. Chang, Phys. Rev. B 84, 195463 (2011).
[2] M.-K. Lee, N.-Y. Lue, C.-K. Wen, and G. Y. Wu, Phys. Rev. B 86, 165411 (2012).
[3] G. Y. Wu, N.-Y. Lue, and Y.-C. Chen, Phys. Rev. B 88, 125422 (2013).

Keywords: valley filter, transition metal dichalcogenides, valleytronics