Superconducting Properties of the Non-Centrosymmetric Superconductor Re6Hf

TL;DR

This paper reports the synthesis and detailed characterization of Re6Hf, a noncentrosymmetric superconductor with a transition temperature around 6 K, exhibiting both conventional and unconventional superconducting features.

Contribution

It provides comprehensive experimental data on Re6Hf's structure, superconducting properties, and thermodynamics, highlighting potential unconventional behavior and triplet pairing possibilities.

Findings

Re6Hf has a cubic noncentrosymmetric alpha-Mn structure.

Superconducting transition temperature is approximately 5.96 K.

Critical fields exceed Pauli limit, indicating unconventional superconductivity.

Abstract

The synthesis and detailed characterization of the noncentrosymmetric superconductor Re$_{6}$Hf using powder x-ray diffraction (XRD), magnetization, transport and thermodynamic measurements are reported. XRD confirms the crystal structure of Re$_{6}$Hf to be cubic noncentrosymmetric $\alpha$-\textit{Mn} with a lattice parameter a = 9.6850(3)\text{\AA}. Resistivity, DC and AC magnetization confirms the bulk superconducting transition T$_{c}^{onset} \sim $ ~ 5.96 K. The lower critical field H$_{C1}(0)\approx$ 5.6 mT and upper critical H$_{C2}(0)$ was found to be around 12.2 T which is greater than the Pauli limiting field, indicating unconventional behavior in Re$_{6}$Hf and leads to the possibility of triplet pairing. A sharp discontinuity in the specific heat data was observed around T$_{c}$ indicating bulk superconductivity, and the normalized specific heat jump is $\Delta C_{el}$/$\gamma_{n}$T$_{c}$ = 1.53 which is in close agreement with BCS value. Superconducting electronic specific heat data is fitted reasonably well for an exponential relation with Sommerfeld coefficient ($\gamma$) showing a linear relation with magnetic field suggesting that in Re$_{6}$Hf dominant pairing channel is s-wave with isotropic superconducting gap parameter without nodes.