Tunneling and Magnetic Characteristics of Superconducting ZrB$_{12}$ Single Crystals

TL;DR

This study investigates the superconducting and magnetic properties of high-quality ZrB$_{12}$ single crystals, revealing surface superconductivity and analyzing the pairing mechanism through various spectroscopic and magnetization measurements.

Contribution

It provides new insights into the surface versus bulk superconducting characteristics of ZrB$_{12}$ and discusses discrepancies in electron-phonon coupling estimates.

Findings

Surface superconductivity observed at fields above the critical field.

Consistent with s-wave pairing from spectroscopy and magnetization data.

Discrepancies in electron-phonon coupling strength estimates.

Abstract

Bulk and surface properties of high-quality single crystals of zirconium dodecaboride have been studied in the temperature range from 4.5 K up to the superconducting transition temperature which is found to be nearly 6.06 K. Scanning tunnelling spectroscopy data, together with dc and ac magnetization measurements, are consistent with the conventional s-wave pairing scenario, whereas they disagree in estimates of the electron-phonon coupling strength. We explain the divergence, supposing a great difference between the surface and bulk superconducting characteristics of the compound. This assertion is supported by our findings of a non-linear magnetic response to an amplitude-modulated alternating magnetic field, testifying to the presence of surface superconductivity in the ZrB$_{12}$ samples at dc fields exceeding the thermodynamic critical field.