Josephson Effect in MgB₂: Large I_cR_N Product and Superconducting Energy Gap

We report the observation of the Josephson effect on the newly
discovered superconductor MgB₂ with break-junction technique. Similar to the conventional superconductors, the I - V curve can be fitted with the resistively shunted junction model including the noise effect, and a large characteristic voltage V_c = I_cR_N = 9.6 meV was obtained. The energy gap determined by the Ambegaokar-Baratoff relation with the fitted V_c is consistent with the Bardeen-Cooper-Schrieffer weak-coupling value well. Our result implies that the superconductor MgB₂ is a promising material for the Josephson device applications.