(Color online) Temperature dependence of the resistance of microbridges A1 and A2. Both were fabricated on the same chip and thus have the same thicknesses of Nb and Au. Au layer of A2 was removed by wet etching. The insert shows the sample geometry and the configuration of the contact leads.
Temperature dependence of the resistance of sample B1 at different magnetic fields applied perpendicular to the plane of the microbridge. Measurements were taken in a PPMS.
Temperature dependence of the upper critical field, B c2. The solid line is a polynomial fit to the data. Results are for sample B1.
(Color online) (a) VICs of A1 (Nb/Au microbridge) under various external magnetic fields. For B a < 0.16 mT, the transition from the zero-voltage state to the normal state is abrupt. Some of the recorded VICs at different B a are not shown for clarity. For 0.165 mT < B a < 2.65 mT, low-voltage dissipation is observed before the onset of the voltage jump to the normal state which is shown in (b). Please notice the small voltage range plotted. Black solid lines are a guide for the eye, indicating linear behaviour. The slopes of the black solid lines just above I p fall in the range of 10–23 mΩ. (c) VICs of A2 (single layer Nb microbridge) in a similar voltage range as sample A1 in (b), indicating the onset of the voltage jump to the normal state is now abrupt at I c in the field range of 0 < B a < 3 mT.
(Color online) The time variation of voltage and temperature for A1 at zero field. The measurement was taken as the bias current increased manually from zero until the voltage suddenly jumped to the level at which the microbridge switched to the normal state. Then, the bias current was kept constant for a period of few minutes, before it was reduced to zero.
(Color online) The dependence of critical current I c and I p on applied field, B a of sample A1, extracted from the VICs in Fig. 4(b). The solid lines are fits using Kim model.
(Color online) (a)–(c) VICs of B1 under various applied magnetic fields. The straight lines (solid or dotted-dashed) are a guide to the eye, indicating linear behaviour before the final voltage jump to the normal state. The two linear branches have resistance values of approximately 15 mΩ and 30 mΩ respectively. (d) VICs of B1 under various applied magnetic fields after the Au layer have been removed by wet etching (single layer Nb microbridge). Please notice a similar voltage range is used as (a)–(c), before Au layer was removed.
(Color online) The time variation of voltage and temperature for B1 under a constant bias current of 11.85 mA and a constant applied magnetic field of 2 mT.
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