Two-band superconductivity with unconventional pairing symmetry in HfV$_2$Ga$_4$

TL;DR

This study reveals that HfV₂Ga₄ exhibits unconventional two-band superconductivity with a nodal s+d-wave order parameter, driven by multiband electronic structure and spin fluctuations, supported by experimental and first-principles calculations.

Contribution

It demonstrates the unconventional multiband superconductivity in HfV₂Ga₄ through combined experimental muon-spin relaxation and first-principles electronic structure analysis.

Findings

Bulk superconductivity at T_c ~ 3.9 K

Nodal two-gap s+d-wave order parameter

Presence of weak spin fluctuations

Abstract

In this letter, we have examined the superconducting ground state of the HfV$_2$Ga$_4$ compound using resistivity, magnetization, zero-field (ZF) and transverse-field (TF) muon-spin relaxation and rotation ($\mu$SR) measurements. Resistivity and magnetization unveil the onset of bulk superconductivity with $T_{\bf c}\sim$ 3.9~K, while TF-$\mu$SR measurements show that the temperature dependence of the superfluid density is well described by a nodal two-gap $s$+$d$-wave order parameter model. In addition, ZF muon relaxation rate increases with decreasing temperature below 4.6 K, indicating the presence of weak spin fluctuations. These observations suggest an unconventional multiband nature of the superconductivity possibly arising from the distinct $d$-bands of V and Hf ions with spin fluctuations playing an important role. To better understand these findings, we carry out first-principles electronic-structure calculations, further highlighting that the Fermi surface consists of multiple disconnected sheets with very different orbital weights and spin-orbit coupling, bridging the way for a nodal multiband superconductivity scenario. In this vein, therefore, HfV$_2$Ga$_4$-family stands out as an open avenue to novel unexplored unconventional superconducting compounds, such as ScV$_2$Ga$_4$ and ZrV$_2$Ga$_4$, and other many rare earths based materials.