Nonadiabatic particle transport in a one-dimensional electron system

Localization, Topology, and Quantized Transport in Disordered Floquet Systems

We investigate the effects of disorder on a periodically driven one-dimensional model displaying quantized topological transport. We show that, while instantaneous eigenstates are necessarily Anderson localized, the periodic driving plays a fundamental role in delocalizing Floquet states over the whole system, henceforth allowing for a steady-state nearly quantized current. Remarkably, this is linked to a localization-delocalization transition in the Floquet states at strong disorder, which occurs for periodic driving corresponding to a nontrivial loop in the parameter space. As a consequence, the Floquet spectrum becomes continuous in the delocalized phase, in contrast with a pure-point instantaneous spectrum.

Nonadiabatic Breaking of Topological Pumping

We study Thouless pumping out of the adiabatic limit. Our findings show that despite its topological nature, this phenomenon is not generically robust to nonadiabatic effects. Indeed, we find that the Floquet diagonal ensemble value of the pumped charge shows a deviation from the topologically quantized limit which is quadratic in the driving frequency for a sudden switch on of the driving. This is reflected also in the charge pumped in a single period, which shows a nonanalytic behavior on top of an overall quadratic decrease. Exponentially small corrections are recovered only with a careful tailoring of the driving protocol. We also discuss thermal effects and the experimental feasibility of observing such a deviation.

Disorder-enhanced dielectric response of nanoscale and mesoscopic insulators

Enhancement of the dielectric response of insulators by disorder is theoretically proposed, where the quantum interference of electronic waves through the nanoscale or mesoscopic system and its change due to external perturbations control the polarization. In the disordered case with all the states being localized, the resonant tunneling, which is topologically protected, plays a crucial role, and enhances the dielectric response by a factor 30-40 compared with the pure case. The realization of this idea with accessible materials or structures is also discussed.

High-frequency single-electron transport in a quasi-one-dimensional GaAs channel induced by surface acoustic waves

We report on an experimental investigation of the direct current induced by transmitting a surface acoustic wave (SAW) with frequency 2.7 GHz through a quasi-one-dimensional (1D) channel defined in a GaAs - AlGaAs heterostructure by a split gate, when the SAW wavelength was approximately equal to the channel length. At low SAW power levels the current reveals oscillatory behaviour as a function of the gate voltage with maxima between the plateaux of quantized 1D conductance. At high SAW power levels, an acoustoelectric current was observed at gate voltages beyond pinch-off. In this region the current displays a step-like behaviour as a function of the gate voltage (or of the SAW power) with the magnitude corresponding to the transfer of one electron per SAW cycle. We interpret this as due to trapping of electrons in the moving SAW-induced potential minima with the number of electrons in each minimum being controlled by the electron - electron interactions. As the number of electrons is reduced, the classical Coulomb charging energy becomes the Mott - Hubbard gap between two electrons and finally the system becomes a sliding Mott insulator with one electron in each well.