Oscillations of the critical superconducting current of thin doubly-connected Sn films in an external perpendicular magnetic field

The results of experimental and theoretical studies of oscillations of the critical superconducting current of thin doubly-connected Sn films in an external perpendicular magnetic field are presented. The experiments were performed on samples that consisted of two wide electrodes joined together by two narrow channels. The length of the channels l satisfied the condition l much greater than x (x being the Ginzburg-Landau coherence length). At temperatures close to the critical temperature T_c, the dependence of critical current I_c on average external magnetic flux F_e has the form of a piece-wise linear function, periodic with respect to flux quantum F₀. The amplitude of I_c oscillations at a given temperature is proportional to the factor x/l. Moreover, the dependence I_c=I_c(F_e), proves to be multivalued, which signifies the presence of metastable states. Based on the Ginzburg-Landau approximation, a theory is constructed that explains the above-mentioned features of the oscillation effect by the example of an ideally symmetric system. Besides, the experiments displayed effects related to the inequality of the critical currents of the superconducting channels, i.e., shifts of the maxima of the dependence I_c=I_c(F_e) accompanied by an asymmetry with respect to a change of the direction of the transport current