Proceedings of nanoGe Fall Meeting19 (NFM19)
DOI: https://doi.org/10.29363/nanoge.nfm.2019.326
Publication date: 18th July 2019
Manipulation of intrinsic electron degrees of freedom, such as charge and spin, gives rise to electronics and spintronics, respectively. Electrons in monolayer materials with a honeycomb lattice structure, such as the Transition-Metal Dichalcogenides (TMD’s), can be classified according to the region (valley) of the Brillouin zone to which they belong. Valleytronics, the manipulation of this electron’s property, is expected to set up a new era in the realm of electronic devices. In this work, we accurately determine the energy spectrum and lifetimes of exciton (electron-hole) bound-states for different TMD materials, namely WSe2, WS2 and MoS2. For all of them, we obtain a splitting of the order of 170 meV between the exciton energies from different valleys, corresponding to an effective Zeeman magnetic field of 1400 T. Our approach, which employs quantum-field theory (QFT) techniques based on the Bethe-Salpeter equation and the Schwinger-Dyson formalism, takes into account the full electromagnetic interaction among the electrons. The valley selection mechanism operates through the dynamical breakdown of the time-reversal (TR) symmetry, which originally interconnects the two valleys. This symmetry is spontaneously broken whenever the full electromagnetic interaction vertex is used to probe the response of the system to an external field.[1]
References
[1] E. C. Marino, Leandro O. Nascimento, Van Sérgio Alves, N. Menezes, C. Morais Smith Quantum Electrodynamical Approach to the Exciton Spectrum in Transition Metal Dichalcogenides, 2D Materials 5 (2018) 041006
[2] A. Chernikov, T. C. Berkelbach, H. M. Hill, A. Rigosi, Y. Li, O. B. Aslan, D. R. Reichman, M. S. Hybertsen, & T. F. Heinz, Exciton Binding Energy and Nonhydrogenic Rydberg Series in Monolayer WS2, Phys. Rev. Lett. 113, (2014). 076802
[3] K. He, N. Kumar, L. Zhao, Z. Wang, K. F. Mak, H. Zhao, & J. Shan, Tightly Bound Excitons in Monolayer WSe2, Phys. Rev. Lett. 113, (2014) 026803
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