Upper critical field pecularities of superconducting YNi2B2C and LuNi2B2C

TL;DR

This study investigates the upper critical field behavior of superconducting YNi2B2C and LuNi2B2C single crystals across a broad temperature range, revealing two-band effects and electronic structure insights.

Contribution

It provides new Hc2(T) data and explains the positive curvature using a two-band model, highlighting limitations of single-band approaches.

Findings

Sizeable positive curvature of Hc2(T) at high and intermediate T

Effective two-band model explains critical field behavior

Evidence for clean limit type II superconductivity

Abstract

We present new upper critical field Hc2(T) data in a broad temperature region from 0.3K to Tc for LuNi2B2C and YNi2B2C single crystals with well characterized low impurity scattering rates. The absolute values for all T, in particular Hc2(0), and the sizeable positive curvature (PC) of Hc2(T) at high and intermediate T are explained quantitatively within an effective two-band model. The failure of the isotropic single band approach is discussed in detail. Supported by de Haas van Alphen data, the superconductivity reveals direct insight into details of the electronic structure. The observed maximal PC near Tc gives strong evidence for clean limit type II superconductors.