Valleytronics - an introduction

In this video I talk about valleytronics: I explain the basic valley physics, valleytronic applications and valleytronic properties. I look in some detail at the valley lifetime of excitons. This video was created to fulfill a graduate course requirement. I do not guarantee that it is error-free. Reading list and resources: ***two other great presentations*** Wang Yao --Valley-spin phenomena in van der Waals heterobilayers: https://www.youtube.com/watch?v=jhOdUb-iyT4 2DCC-MIP Topological Valleytronics Bilayer Graphene Webinar Nov. 2017: https://www.youtube.com/watch?v=iOsout7aVGc ***great reviews*** Vitale, S. A., Nezich, D., Varghese, J. O., Kim, P., Gedik, N., Jarillo‐Herrero, P., Xiao, D., & Rothschild, M. (2018). Valleytronics: Opportunities, Challenges, and Paths Forward. Small, 14(38), 1801483. https://doi.org/10.1002/smll.201801483 Wang, G., Chernikov, A., Glazov, M. M., Heinz, T. F., Marie, X., Amand, T., & Urbaszek, B. (2018). Colloquium: Excitons in atomically thin transition metal dichalcogenides. Reviews of Modern Physics, 90(2), 021001. https://doi.org/10.1103/RevModPhys.90.021001 ***valley physics*** Xiao, D., Yao, W., & Niu, Q. (2007). Valley-Contrasting Physics in Graphene: Magnetic Moment and Topological Transport. Physical Review Letters, 99(23), 236809. https://doi.org/10.1103/PhysRevLett.99.236809 Yao, W., Xiao, D., & Niu, Q. (2008). Valley-dependent optoelectronics from inversion symmetry breaking. Physical Review B, 77(23), 235406. https://doi.org/10.1103/PhysRevB.77.235406 Xiao, D., Liu, G.-B., Feng, W., Xu, X., & Yao, W. (2012). Coupled Spin and Valley Physics in Monolayers of MoS2 and Other Group-VI Dichalcogenides. Physical Review Letters, 108(19), 196802. https://doi.org/10.1103/PhysRevLett.108.196802 ***experimental confirmation*** Cao, T., Wang, G., Han, W., Ye, H., Zhu, C., Shi, J., Niu, Q., Tan, P., Wang, E., Liu, B., & Feng, J. (2012). Valley-selective circular dichroism of monolayer molybdenum disulphide. Nature Communications, 3(1), 1–5. https://doi.org/10.1038/ncomms1882 Mak, Kin Fai, He, K., Shan, J., & Heinz, T. F. (2012). Control of valley polarization in monolayer MoS 2 by optical helicity. Nature Nanotechnology, 7(8), 494–498. https://doi.org/10.1038/nnano.2012.96 Mak, K. F., McGill, K. L., Park, J., & McEuen, P. L. (2014). The valley Hall effect in MoS2 transistors. Science, 344(6191), 1489–1492. https://doi.org/10.1126/science.1250140 Lee, J., Mak, K. F., & Shan, J. (2016). Electrical control of the valley Hall effect in bilayer MoS 2 transistors. Nature Nanotechnology, 11(5), 421–425. https://doi.org/10.1038/nnano.2015.337 ***valley lifetime*** Yu, H., Liu, G.-B., Gong, P., Xu, X., & Yao, W. (2014). Dirac cones and Dirac saddle points of bright excitons in monolayer transition metal dichalcogenides. Nature Communications, 5(1), 1–7. https://doi.org/10.1038/ncomms4876 Yu, T., & Wu, M. W. (2014). Valley depolarization due to intervalley and intravalley electron-hole exchange interactions in monolayer MoS2. Physical Review B, 89(20), 205303. https://doi.org/10.1103/PhysRevB.89.205303 Kim, J., Jin, C., Chen, B., Cai, H., Zhao, T., Lee, P., Kahn, S., Watanabe, K., Taniguchi, T., Tongay, S., Crommie, M. F., & Wang, F. (2017). Observation of ultralong valley lifetime in WSe2/MoS2 heterostructures. Science Advances, 3(7), e1700518. https://doi.org/10.1126/sciadv.1700518 Tang, Y., Mak, K. F., & Shan, J. (2019). Long valley lifetime of dark excitons in single-layer WSe2. Nature Communications, 10. https://doi.org/10.1038/s41467-019-12129-1 Maialle, M. Z., de Andrada e Silva, E. A., & Sham, L. J. (1993). Exciton spin dynamics in quantum wells. Physical Review B, 47(23), 15776–15788. https://doi.org/10.1103/PhysRevB.47.15776