Precursor diamagnetism above the superconducting transition in YNi_mathsf{2}B_mathsf{2}C

High-resolution SQUID magnetization measurements in a single crystal of YNi₂B₂C around the superconducting transition are reported. The diamagnetic magnetization -M _fl at constant field H as a function of temperature and isothermal magnetization curves -M _fl vs. H are used to derive insights on precursor phenomena approaching the bulk transition temperature K. The precursor diamagnetism is found strongly enhanced with respect to the conventional Ginzburg-Landau value for Gaussian fluctuations and the curves -M _fl vs. H exhibit an upturn with the field and hysteretic effects up to T ^* = 15.4 K. These results are interpreted in terms of a non-zero order parameter in superconducting droplets above the bulk T _c . These droplets are likely to be related to inhomogeneities resulting from small amount of boron to carbon substitutions.Received: 23 April 2003, Published online: 15 October 2003PACS: 74.40.+k Fluctuations (noise, chaos, nonequilibrium superconductivity, localization, etc.) - 74.20.De Phenomenological theories (two-fluid, Ginzburg-Landau, etc.) - 74.25.Ha Magnetic properties