Josephson tunneling in MgB 2 break junctions

Josephson effects in break junctions of MgB ₂ sintered at ambient pressure, have been investigated. The measured I- V characteristics of the junctions and the current step heights of the Shapiro steps can well be fitted with the resistively shunted junction model. Relatively large I_cR_n was obtained, which ranges from 1.4 to 4.2 mV. The temperature dependence of the Josephson critical current indicated that our break junctions were of the SNS weak link. The apparent deviation in the Fraunhofer pattern implied inhomogeneous current flow in the MgB ₂ break junctions.