Transport properties and lower critical field of Josephson junctions

摘要

We prepared Josephson junctions based on artificial grain boundaries in thin epitaxial Bi_2Sr_2Ca_2Cu_3O_(10+δ) films. The Josephson junctions show an I_cR_n product of 0.1 mV, 0.7 mV and 1 mV for 45°, 36.8° and 24° grain boundary angles respectively. The 36.8°grain boundary junctions are hysteretic for T = 4.2 K and follow the tesistively shunted junction (RSJ) model for temperatures above 50 K. The 24° grain boundary junctions are RSJ-like over the whole temperature range. The critical current density was measured and compared to the theoretical values from the Ambegaokar-Baratoff theory for s-wave superconductor and a d_(x~2-y~2)-wave model. The magnetic field dependence of the critical current was used to determine the lower critical Held of the Josephson junction. The values are in good agreement with calculations of the lower critical field with a thermodynamic approach.