MAGNETIC-FIELD DEPENDENCE OF THE LONDON PENETRATION DEPTH OF BI2SR2CACU2OY

London penetration depth λL was investigated as a function of dc magnetic field H in the Meissner state of Bi2Sr2CaCu2Oy. At low temperatures, λL changes linearly in H, which is in contrast to the H2 behavior observed in conventional superconductors. With increasing temperature, systematic rounding around zero field was observed. Together with the comparative study for a conventional superconductor V3Si, it is suggested that the superconducting state of Bi2Sr2CaCu2Oy is unconventional. These findings are the first confirmation of a recent new theoretical prediction for d-wave superconductors. © 1995 The American Physical Society.