Conductance oscillations in mesoscopic rings:: Microscopic versus global phase

The phase of Aharonov-Bohm oscillations in mesoscopic diffusive metal rings in the presence of a magnetic field, can be modulated by the application of a dc-bias current I-dc. We address the question of how a variation of I-dc and hence of the microscopic phases of the electronic wave functions results in the observable "global" phase of the conductance oscillations. Whereas the first one can be varied continuously, the latter has to be quantized for a ring in a two-wire configuration by virtue of the Onsager symmetry relations. We observe a correlation between a phase flip by +/-pi and the amplitude of the oscillations.