Precursor diamagnetism above the superconducting transition in YNi $_\mathsf{2}$ B $_\mathsf{2}$ C

Abstract

High-resolution SQUID magnetization measurements in a single crystal of YNi2B2C around the superconducting transition are reported. The diamagnetic magnetization −Mfl at constant field H as a function of temperature and isothermal magnetization curves −Mfl vs. H are used to derive insights on precursor phenomena approaching the bulk transition temperature Tc(H =0 ) =1 5.25 ± 0.02 K. The precursor diamagnetism is found strongly enhanced with respect to the conventional Ginzburg-Landau value for Gaussian fluctuations and the curves −Mfl vs. H exhibit an upturn with the field and hysteretic effects up to T ∗ =1 5.4 K. These results are interpreted in terms of a non-zero order parameter in super- conducting droplets above the bulk Tc. These droplets are likely to be related to inhomogeneities resulting from small amount of boron to carbon substitutions.