Evidence for Current-Flow Anomalies in the Irradiated 2D Electron System at Small Magnetic Fields

Abstract

We report experimental transport results in 2D electron systems exposed to dipole radiation up to 20 GHz. Magnetoresistance oscillations occur as seen with higher frequency radiation; however, minima here can be seen to extend to negative biases, and zeros are not observed persistently around sample perimeters. Under radiation, voltages are generated from internal to external contacts in the absence of applied driving currents. These findings may be consistent with theoretical pictures of current instabilities due to local negative resistivities.

Zero-Differential Resistance State of Two-Dimensional Electron Systems in Strong Magnetic Fields

“…Strong oscillations of the longitudinal resistance induced by microwave radiation have been found at magnetic fields which satisfy the condition ω = n × ω c , where ω is the microwave frequency, ω c is cyclotron frequency and n=1,2.... [1,2] At high levels of the microwave excitations the minima of the oscillations can reach value close to zero. [3,4,5,6] This so-called zero resistance state (ZRS) has stimulated extensive theoretical interest. [7,8,9,10,11,12] At higher magnetic field ω c > ω a considerable decrease of magnetoresistance with microwave power is found [2,5,6] which has been attributed to intra-Landau-level transitions.…”

“…[3,4,5,6] This so-called zero resistance state (ZRS) has stimulated extensive theoretical interest. [7,8,9,10,11,12] At higher magnetic field ω c > ω a considerable decrease of magnetoresistance with microwave power is found [2,5,6] which has been attributed to intra-Landau-level transitions. [13] Another interesting nonlinear phenomena have been observed in response to DC electric field.…”

Temperature effects on microwave-induced resistivity oscillations and zero-resistance states in two-dimensional electron systems

“…Very few experiments in the field of Condensed Matter Physics have produced such intense theoretical and experimental activities in the recent years as the one of longitudinal magnetoresisitvity (ρ xx ) oscillations and zero resistance states (ZRS) [1,2,3,4]. These are obtained when a two dimensional electron gas (2DEG) is subjected simultaneously to the influence of a moderate magnetic field (B) and microwave (MW) radiation.…”

“…Among all those contributions only very few of them have been devoted fully or partially to the study of the influence of T [10,11,12]. Experimental evidence [1,2,3,4] shows two common features concerning the dependence of ρ xx with T : the first one is a reduction of ρ xx oscillation amplitude as T is increased, eventually disappearing ZRS; the second one is the Tvariation of ρ xx at the deepest minima which suggests thermally activated transport, that is, ρ xx ∝ exp( −Eact kB T ) where E act is the activation energy [1,2,4]. In this paper we develop a microscopic model to explain most experimental results that involve the effect of T .…”

Oscillatory nonlinear differential magnetoresistance of highly mobile 2D electrons in high Landau levels

“…These resistance oscillations always occur at low temperatures and are related to magnetotransport of 2D electrons occupying high Landau levels (LLs). Among them the microwave-induced magnetoresistance oscillations and the related zero-resistance states were the central focus of most experimental 1,2,3,4,5,6,7,8,9,10 and theoretical 11,12,13,14,15,16,17,18,19,20,21 studies. Recently, the oscillatory behavior in the nonlinear magnetotransport has attracted much attention: in a 2D system even without irradiation, a relatively weak current can induce drastic suppression and strong oscillations of the differential magnetoresistance, and may result in a state of zero-differential resistance.…”