Ensemble-Average Spectrum of Aharonov-Bohm Conductance Oscillations: Evidence for Spin-Orbit-Induced Berry's Phase

We have experimentally investigated Aharonov-Bohm conductance oscillations in two-dimensional rings in the presence of a strong Rashba spin-orbit interaction. The peak of the ensemble average spectrum corresponding to the h/e oscillations is split in several samples. We argue that the splitting originates from the geometric phase acquired by an electron spin under the influence of the spin-orbit interaction. Our results demonstrate how the ensemble average spectrum provides information otherwise not easily accessible.