Linear temperature dependence of lower critical field in MgB2 - art. no. 094522

The lower critical field H-c1 has been carefully measured on a well-shaped cylindrical dense sample of the new superconductor MgB2 fabricated by high- pressure synthesis. The penetration depth lambda is calculated from the H-c 1 data. It is found that a linear relation of H-c1(T) appears in the whole temperature region below T-c. Furthermore, a finite slope of dH(c1)/dT and d lambda (T)/dT remains down to the lowest temperature (2 K). These are inc onsistent with the expectation for an isotropic s-wave superconductivity in MgB2.