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

Abstract

We report the results of experimental and theoretical studies of critical current oscillations in thin doubly-connected Sn films in an external perpendicular magnetic field. 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 ≫ ξ (ξ is the Ginzburg–Landau coherence length). At temperatures close to the critical temperature Tc, the dependence of the critical current Ic on average external magnetic flux Φ¯e has the form of a piecewise linear function, periodic with respect to the flux quantum Φ0. The amplitude of the Ic oscillation at a given temperature is proportional to the factor ξ/l. Moreover, the dependence Ic=Ic(Φ¯e) is found to be multivalued, hence indicating the presence of metastable states. Based on the Ginzburg–Landau approximation, a theory was constructed that explains the above features of the oscillation phenomenon taking a perfectly symmetric system as an example. Further, the experiments displayed the effects related to the critical currents imbalance between the superconducting channels, i.e., shift of the maxima of the dependence Ic=Ic(Φ¯e) accompanied by an asymmetry with respect to the transport current direction.

Asymmetric nanowire SQUID: Linear current-phase relation, stochastic switching, and symmetries

“…Additionally, many computationally advanced models based on Ginzburg-Landau theory have been developed [22,24,25]. Here, we have shown that a simple model based on a linear CPR provides excellent fits to our critical current data.…”

“…Furthermore, we observe that the regions of stability of the vorticity, namely the Little-Parks diamonds [24,31,32], can overlap significantly, thus generating multivaluedness of the critical current and of the vorticity at a fixed magnetic field. Yet we find some magnetic field -bias current parameter regions, which we call uniquevorticity diamonds, in which only one vorticity is stable.…”

“…Advanced computational simulations based on Ginzburg-Landau theory, which is known to be valid at temperatures near the critical temperature T C [30], have been used to simulate the critical current versus field dependence of nanowire loops previously [22,24,25]. While some of these computational models do calculate a piecewise linear or near-linear dependence of critical current on magnetic field [22,24], these authors do not present theoretical analysis of cases in which the loop is asymmetric. Additionally, none plot theory on top of experimental data to allow direct comparison of the two.…”

“…We also observe that the general shape of the I C (B) curve is made of linear segments rather than being sinusoidal. At temperatures much lower than T C , a linear CPR (and therefore a linear relationship between critical current and field) is both expected [2,[26][27][28][29] and has been observed experimentally [13,15,[22][23][24]. Advanced computational simulations based on Ginzburg-Landau theory, which is known to be valid at temperatures near the critical temperature T C [30], have been used to simulate the critical current versus field dependence of nanowire loops previously [22,24,25].…”

Spontaneous emergence of Josephson junctions in homogeneous rings of single-crystal Sr2RuO4

“…Since ( ) varies with temperature while remains fixed, the CPR of such weak links is strongly temperature dependent. Generally, lowering the temperature transforms the CPR from sinusoidal to a sawtooth-like function, which ultimately turns into multivalued relations once ≳ 3.5 ( ), corresponding to the nucleation of phase-slip centres [33,34,35]. The multivalued CPR manifests itself as a hysteretic ( ) relation, which is a well-known characteristic of constriction junctions at ≪ [36,37].…”