Extracting the diffusivity ratio from point contact Andreev reflection spectroscopy and upper critical field measurements in MgB2

Abstract

The diffusivity ratio η, which measures the relative intraband scattering in the π and σ bands in MgB2 has been determined by fitting the Hc2 (T) at T ∼ Tcand by Point Contact Andreev Reflection. We find a satisfactory agreement between the values for η obtained by both methods for c-axis orientated MgB2 thin films. Point contact Andreev Reflection was then applied to bulk MgB2 containing Mg vacancies. Spectra obtained in zero field indicate a distribution of the two gaps Δσ,π but no merging of the values with increased magnesium deficiency. Spectra fitted as a function of field are consistent with an increase in π intraband scattering with increasing magnesium deficiency. Measurement of the point contact Andreev reflection spectra as a function of temperature revealed features not immediately expected from current theoretical models. © 2008 IOP Publishing Ltd.