Zero-resistance states induced by electromagnetic-wave excitation in GaAs/AlGaAs heterostructures

The observation of vanishing electrical resistance in condensed matter has led to the discovery of new phenomena such as, for example, superconductivity, where a zero-resistance state can be detected in a metal below a transition temperature T-c (ref. 1). More recently, quantum Hall effects were discovered from investigations of zero-resistance states at low temperatures and high magnetic fields in two-dimensional electron systems (2DESs)(2-4). In quantum Hall systems and superconductors, zero-resistance states often coincide with the appearance of a gap in the energy spectrum(1,2,4). Here we report the observation of zero-resistance states and energy gaps in a surprising setting(5) : ultrahigh-mobility GaAs/AlGaAs heterostructures that contain a 2DES exhibit vanishing diagonal resistance without Hall resistance quantization at low temperatures and low magnetic fields when the specimen is subjected to electromagnetic wave excitation. Zero-resistance states occur about magnetic fields B=4/5B(f) and B=4/9B(f), where B-f=2pifm*/e;m* is the electron mass, e is the electron charge, and f is the electromagnetic-wave frequency. Activated transport measurements on the resistance minima also indicate an energy gap at the Fermi level(6). The results suggest an unexpected radiation-induced, electronic-state-transition in the GaAs/AlGaAs 2DES.