CPM Seminar

Current Flow in Microwave-Induced Zero-Resistance States

Rui-Rui Du

Department of Physics and Astronomy
Rice University

Microwave can induce remarkable new phenomena in the dc transport of a high-mobility two-dimensional electron system (2DES). Surprising new 1/B resistance oscillations, as well as “zero-resistance states (ZRS)”, were discovered in Hall samples of GaAs/AlGaAs heterostructures. Alternatively, “zero-conductance states” have been observed in Corbino samples. Current theories suggest that the ZRS can be understood by the presence of non-equilibrium 2D electron states under microwaves and the consequent formation of electrical current domains. This talk will present new experimental results on some aspects of the phenomena. We first report on a strong suppression of oscillation and ZRS by a modest parallel magnetic field. Our experiments show that the oscillations become substantially weakened in a B_// and are completely suppressed at B_// > 1 T. Although both Zeeman energy _// and scattering times of the 2DES are affected by B_//, analysis shows that these influences are small and cannot account for the observations. In contrast to the ZRS, the magnetoplasmon resonances, which are also observed in the same samples, become stronger in B_//. In the second part of the talk we will report on results for bichromatic experiments (frequency i₁, i₂). It is found that for nonzero-resistance states the resultant resistance was the average of the values corresponding to the two frequencies separately. On the other hand, when the measurements included frequencies that had yielded a zero resistance, the bichromatic resistance is dramatically reduced. We discuss the interpretation of these results in terms of electron flow pattern, as proposed by theories, and the prospect for imaging these patterns in low temperature scanning Hall microscopy experiments.