1. Gordon McKay Laboratory of Applied Science, Harvard University, 9 Oxford Street, Cambridge, Massachusetts 02138, USA
2. Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany
3. Pierce Hall, Harvard University, 29 Oxford Street, Cambridge, Massachusetts 02138, USA
4. Laboratory for Physical Sciences, University of Maryland, College Park, Maryland 20740, USA
5. Braun Center for Submicron Research, Weizmann Institute, Rehovot 76100, Israel

Correspondence to: Ramesh G. Mani^1,2 Correspondence and requests for materials should be addressed to R.G.M. (e-mail: Email: mani@deas.harvard.edu).

Abstract

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, 3, 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 setting⁵: 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 = 4/5 B_f and B = 4/9 B_f, where B_f = 2fm*/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 level⁶. The results suggest an unexpected radiation-induced, electronic-state-transition in the GaAs/AlGaAs 2DES.