Doping-induced superconductivity of ZrB$_2$ and HfB$_2$

TL;DR

This study investigates how small amounts of vanadium doping induce superconductivity in ZrB₂ and HfB₂, revealing their magnetic and electronic properties and comparing them to MgB₂ within a multiband superconductivity framework.

Contribution

It provides a comparative analysis of doped ZrB₂ and HfB₂ superconductors, including experimental measurements and electronic structure calculations, highlighting differences from MgB₂.

Findings

Vanadium doping induces superconductivity in ZrB₂ and HfB₂.

Magnetic and superconducting properties are characterized and compared.

Electronic structure calculations reveal differences from MgB₂.

Abstract

Unlike the widely studied $s$-type two-gap superconductor MgB$_2$, the chemically similar compounds ZrB$_2$ and HfB$_2$ do not superconduct above 1 K. Yet, it has been shown that small amounts of self- or extrinsic doping (in particular with vanadium), can induce superconductivity in these materials. Based on results of different macro- and microscopic measurements, including magnetometry, nuclear magnetic resonance (NMR), resistivity, and muon-spin rotation ($\mu$SR), we present a comparative study of Zr$_{0.96}$V$_{0.04}$B$_2$ and Hf$_{0.97}$V$_{0.03}$B$_2$. Their key magnetic and superconducting features are determined and the results are considered within the theoretical framework of multiband superconductivity proposed for MgB$_2$. Detailed Fermi surface (FS) and electronic structure calculations reveal the difference between MgB$_2$ and transition-metal diborides.