Point contact Andreev reflection spectroscopy of NdFeAsO_0.85

TL;DR

This study uses point contact Andreev reflection spectroscopy to measure the superconducting gap in NdFeAsO0.85, revealing a gap of about 7meV and suggesting complex underlying physics.

Contribution

It provides the first detailed spectroscopic measurement of the superconducting gap in NdFeAsO0.85, highlighting potential complexities in its superconducting state.

Findings

Superconducting gap of approximately 7meV at 4.2K.

Spectra vary with contact pressure, indicating complex physics.

Consistent gap value with previous oxypnictide studies.

Abstract

The newly discovered oxypnictide family of superconductors show very high critical temperatures of up to 55K. Whilst there is growing evidence that suggests a nodal order parameter, point contact Andreev reflection spectroscopy can provide crucial information such as the gap value and possibly the number of energy gaps involved. For the oxygen deficient NdFeAsO0.85 with a Tc of 45.5K, we show that there is clearly a gap value at 4.2K that is of the order of 7meV, consistent with previous studies on oxypnictides with lower Tc. Additionally, taking the spectra as a function of gold tip contact pressure reveals important changes in the spectra which may be indicative of more complex physics underlying this structure.