Glass-like low frequency ac response of ZrB$_{12}$ and Nb single crystals in the surface superconducting state

TL;DR

This study investigates the low frequency ac response of ZrB$_{12}$ and Nb single crystals in the surface superconducting state, revealing glass-like behavior and large losses at ultra low frequencies through susceptibility measurements.

Contribution

It provides new insights into the electrodynamics of surface superconductivity, including frequency-dependent susceptibility and surface wave function characteristics.

Findings

Logarithmic frequency dependence of susceptibility in surface superconducting state

Large losses observed at frequencies below 3 Hz

Surface wave function slope determined

Abstract

We report experimental studies of the low frequency electrodynamics of ZrB$_{12}$ and Nb single crystals. AC susceptibility at frequencies 3 - 1000 Hz have been measured under a dc magnetic field, $H_0$, applied parallel to the sample surface. In the surface superconducting state, for several $H_0$, the real part of the ac magnetic susceptibility exhibits a logarithmic frequency dependence as for spin-glass systems. Kramers-Kronig analysis of the experimental data, shows large losses at ultra low frequencies ($<3$ Hz). The wave function slope at the surface was found. The linear response of the order parameter to the ac excitation was extracted from the experimental data.