Photoinduced Nonperturbative Valley Polarization in Graphene

Photoinduced valley-polarized current of layered MoS2 by electric tuning

A photoinduced current of a layered MoS2-based transistor is studied from first-principles. Under the illumination of circular polarized light, a valley-polarized current is generated, which can be tuned by the gate voltage. For monolayer MoS2, the valley-polarized spin-up (down) electron current at K (K') points is induced by the right (left) circular polarized light. The valley polarization is found to reach +1.0 (-1.0) for the valley current that carried such a K (K') index. For bilayer MoS2, the spin-up (down) current can be induced at both K and K' valleys by the right (left) circular lig…

Photoinduced quantum spin and valley Hall effects and orbital magnetization in monolayer MoS2

We theoretically demonstrate that 100\% valley-polarized transport in monolayers of MoS$_{2}$ and other group-VI dichalcogenides can be obtained using off-resonant circularly polarized light. By tuning the intensity of the off-resonant light the intrinsic band gap in one valley is reduced, while it is enhanced in the other valley, enabling single valley quantum transport. As a consequence, we predict (i) enhancement of the longitudinal electrical conductivity, accompanied by an increase in the spin-polarization of the flowing electrons, (ii) enhancement of the intrinsic spin Hall effect, toget…

Nonequilibrium Theory of Photoinduced Valley Hall Effect

A recent scientific debate has arisen: Which processes underlie the actual ground of the valley Hall effect (VHE) in two-dimensional materials? The original VHE emerges in samples with ballistic transport of electrons due to the anomalous velocity terms resulting from the Berry phase effect. In disordered samples though, alternative mechanisms associated with electron scattering off impurities have been suggested: (i) asymmetric electron scattering, called skew scattering, and (ii) a shift of the electron wave packet in real space, called a side jump. It has been claimed that the side jump not…

Photoinduced valley and electron-hole symmetry breaking in $ α$-$T_3$ lattice: The role of a variable Berry phase

We consider $α$-$T_3$ lattice illuminated by intense circularly polarized radiation in terahertz regime. We present quasienergy band structure, time-averaged energy spectrum and time-averaged density of states of $α$-$T_3$ lattice by solving the Floquet Hamiltonian numerically. We obtain exact analytical expressions of the quasienergies at the Dirac points for all values of $α$ and field strength. We find that the quasienergy band gaps at the Dirac point decrease with increase of $α$. Approximate forms of quasienergy and band gaps at single and multi-photon resonant points are derived using ro…

单层1T$^\prime$-MoS$_2$中的光诱导拓扑相变

Photoinduced topological phase transition in monolayer 1T$^\prime$-MoS$_2$

本文采用低能$k\cdot p$哈密顿量结合范弗莱克展开研究高频圆偏振驱动下单层1T$^\prime$-MoS$_2$的非平衡拓扑相，揭示了光控拓扑相变规律，证实其为实现非平衡拓扑相的可调谐平台。

单层Ti$_2$SiCO$_2$中的光诱导拓扑相变

Photoinduced topological phase transition in monolayer Ti$_2$SiCO$_2$

基于紧束缚模型和Floquet理论，研究了单层Ti$_2$SiCO$_2$在激光和电场下的光诱导拓扑相变，发现圆偏振光可使其从二阶拓扑绝缘体转变为陈数为±2的陈绝缘体，并揭示了丰富的拓扑相图，拓展了其在光电器件中的应用。