Effect of two bands on critical fields in MgB2 thin films with various resistivity values

TL;DR

This study measures the upper critical fields of MgB2 thin films with varying resistivities, revealing a linear temperature dependence and independence from resistivity, and analyzes the multiband superconductivity effects.

Contribution

It provides new insights into how multiband effects influence critical fields and resistivity in MgB2 thin films, challenging BCS theory predictions.

Findings

Critical fields range from 13-24 T perpendicular and 42-57 T in-plane.

No saturation of critical fields at low temperatures, linear dependence observed.

Critical fields are independent of normal state resistivity.

Abstract

Upper critical fields of four MgB2 thin films were measured up to 28 Tesla at Grenoble High Magnetic Field Laboratory. The films were grown by Pulsed Laser Deposition and showed critical temperatures ranging between 29.5 and 38.8 K and resistivities at 40 K varying from 5 to 50 mWcm. The critical fields in the perpendicular direction turned out to be in the 13-24 T range while they were estimated to be in 42-57 T the range in ab-planes. In contrast to the prediction of the BCS theory, we did not observe any saturation at low temperatures: a linear temperature dependence is exhibited even at lowest temperatures at which we made the measurements. Moreover, the critical field values seemed not to depend on the normal state resistivity value. In this paper, we analyze these data considering the multiband nature of superconductivity in MgB2 We will show how the scattering mechanisms that determine critical fields and resistivity can be different.