Hall detection of time-reversal symmetry breaking under AC electric driving.

In a four terminal sample, microscopic time reversibility leads to symmetry relations between resistance measurements where the role of current and voltage leads are exchanged. These reciprocity relations are a manifestation of general Onsager-Casimir symmetries in equilibrium systems. We investigate experimentally the validity of time-reversal symmetry in a GaAs/Ga_{1-x}Al_{x}As Hall bar irradiated by an external ac field, at a zero magnetic field. For inhomogeneous ac fields, we find strong deviations from reciprocity relations and show that their origin can be understood from the billiard model of a Hall junction. Under homogeneous irradiation, the symmetry is more robust, indicating that time-reversal symmetry is preserved.