Quantum-electrodynamical approach to the exciton spectrum in Transition-Metal Dichalcogenides

Abstract

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 distinguished 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 WSe${}_2$, WS${}_2$ and MoS${}_2$. 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.

References in corpus (13)

• Excitons in atomically thin transition metal dichalcogenides
• Tightly bound excitons in monolayer WSe2
• Valley-Polarized Metals and Quantum Anomalous Hall Effect in Silicene
• Magnetic Control of Valley Pseudospin in Monolayer WSe2
• Valley Zeeman Effect in Elementary Optical Excitations of a Monolayer WSe2
• Breaking of valley degeneracy by magnetic field in monolayer MoSe2
• Photo-Induced Topological Phase Transition and a Single Dirac-Cone State in Silicene
• Valley Splitting and Polarization by the Zeeman Effect in Monolayer MoSe2
• Spin-Valleytronics in Silicene: Quantum-Spin-Quantum-Anomalous Hall Insulators and Single-Valley Semimetals
• Ultrafast Generation of Pseudo-magnetic Field for Valley Excitons in WSe2 Monolayers
• Ultrafast Manipulation of Valley Pseudospin
• Excitonic effects in the optical properties of 2D materials: An equation of motion approach
• Unitarity of theories containing fractional powers of the d'Alembertian operator

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