  Magnetic field dependences of critical current, resistance, and rectified
voltage of asymmetric (half circles of different widths) and symmetrical (half
circles of equal widths) aluminum rings were measured in the temperature region
close to the superconducting transition. All these dependences are periodic
magnetic field functions with periods corresponding to the flux quantum in the
ring. The periodic dependences of critical current measured in opposite
directions were found to be close to each other for symmetrical rings and
shifted with respect to each other by half the flux quantum in asymmetric rings
with ratios between half circle widths of from 1.25 to 2. This shift of the
dependences by a quarter of the flux quantum as the ring becomes asymmetric
makes critical current anisotropic, which explains the rectification effect
observed for asymmetric rings. Shifts of the extrema of the periodic
dependences of critical current by a quarter of the flux quantum contradict
directly to the results obtained by measuring asymmetric ring resistance
oscillations, whose extrema are, as for symmetrical rings, observed at magnetic
fluxes equal to an integer and a half of flux quanta.
