Unconventional superconductivity of NdFeAsO0.82F0.18 indicated by the low temperature dependence of the lower critical field Hc1

TL;DR

This study investigates the unconventional superconductivity in NdFeAsO0.82F0.18, revealing a nodal gap structure and potential multi-gap features through low temperature measurements of the lower critical field.

Contribution

It provides experimental evidence of unconventional, possibly multi-gap superconductivity in NdFeAsO0.82F0.18 based on low temperature Hc1 behavior.

Findings

Hc1 shows linear temperature dependence at low temperatures

Indicates non-s-wave, unconventional superconductivity

Suggests presence of multi-gap features

Abstract

We measured the initial M-H curves for a sample of the newly discovered superconductor NdFeAsO0.82Fe0.18, which had a critical temperature, Tc, of 51 K, and was fabricated at the high pressure of 6 GPa. The lower critical field, Hc1, was extracted from the deviation point of the Meissner linearity in the M-H curves, which show linear temperature dependence in the low temperature region down to 5 K. The Hc1(T) indicates no s-wave superconductivity, but rather an unconventional superconductivity with a nodal gap structure. Furthermore, the linearity of Hc1 at low temperature does not hold at high temperature, but shows other characteristics, indicating that this superconductor might have multi-gap features. Based on the low temperature nodal gap structure, we estimate that the maximum gap magnitude delta 0 = (1.6+- 0.2) kBTc.