Measurement of the Current-Phase Relation of a Niobium-Nitride Bridge in the Non-Hysteretic Regime Using a SQUID.
The static current-phase relation, I ((phi)), has been determined by measuring the induced flux as a function of the external field for granular NbN weak links incorporated in a superconducting ring. The measurement was made using a SQUID magnetometer. We find a temperature -independent kinetic inductance together with a sinusoidal component resulting in a current-phase relation expressed implicitly in the form (phi)(i) = 2(pi)/(PHI)(,0) (iL(,k)) + arcsin(i/i(,c)). The value of L(,k) for these bridges, whose dimensions are from 1-50 (mu)m in width by 1 (mu)m in length is approximately 1.2 x 10('-10)H. A kinetic inductance of this magnitude is consistent with a model of small grains of superconducting material separated by Josephson barriers. Furthermore, the critical current versus temperature has been measured. Although it is more linear than corresponding data taken at microwave frequencies, the magnitudes of the maximum critical currents and normal resistances are similar (20-59 (mu)a and 25-50(OMEGA) respectively). The linearity of the data may be attributable to flux-flow.
- Pub Date:
- Physics: Condensed Matter