UPPER CRITICAL-FIELD IN BOROCARBIDES

Resistive measurement of superconducting transitions under externally applied magnetic fields in polycrystalline samples of YPd5B3C0.3 and Y Ni2B2C has revealed a marked positive curvature in the temperature dep endence of H-c2, with the slope - dH(c2)/dT increasing monotonically f rom T-c to 4.2 K. This observed positive curvature is in marked contra st with the predictions of the conventional theories of upper critical field. It is possible that a compensation mechanism may have to be in voked to account for the observed results.