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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 () 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 () index. For bilayer MoS2, the spin-up (down) current can be induced at both K and valleys by the right (left) circular light. In contrast to monolayer MoS2, the photoinduced valley polarization shows asymmetric behavior upon reversal of the gate voltage. Our results show that the valley polarization of the photoinduced current can be modulated by the circular polarized light and the gate voltage. All the results can be well understood using a simple kp model. [ABSTRACT FROM AUTHOR]

We report an investigation of the dynamic conductance fluctuation of disordered mesoscopic conductors including one-dimensional, two-dimensional, and quantum dot systems. Our numerical results show that in the quasi-ballistic regime the average emittance is negative, indicating the expected inductive-like behavior. However, in the diffusive and localized regime, the average emittance is still negative. This disagrees qualitatively with the result obtained from random matrix theory. Our analysis suggests that this counterintuitive result is due to the appearance of non-diffusive elements in the system, the necklace states (or the precursor of necklace states in the diffusive regime) whose existence has been confirmed experimentally in an optical system. [ABSTRACT FROM AUTHOR]