Vortex phases and glassy dynamics in the highly anisotropic superconductor HgBa$_2$CuO$_{4+\delta}$

TL;DR

This study investigates vortex behavior in the highly anisotropic superconductor HgBa$_2$CuO$_{4+eta}$, revealing detailed phase diagrams and dynamic regimes, including glassy states and elastic-to-plastic transitions, through magnetization and vortex creep measurements.

Contribution

It provides a comprehensive vortex phase diagram and identifies the crossover from elastic to plastic vortex dynamics in a highly anisotropic superconductor.

Findings

Vortex phase diagram with exponential decay of key fields at low T

Glassy vortex behavior with collective creep of 2D pancake vortices

Elastic-to-plastic crossover coinciding with the second magnetization peak

Abstract

We present an extensive study of vortex dynamics in a high-quality single crystal of HgBa$_2$CuO$_{4+\delta}$ (Hg1201), a highly anisotropic superconductor that is a model system for studying the effects of anisotropy. From magnetization $M$ measurements over a wide range of temperatures $T$ and fields $H$, we construct a detailed vortex phase diagram. We find that the temperature-dependent vortex penetration field $H_p(T)$, second magnetization peak $H_{smp}(T)$, and irreversibility field $H_{irr}(T)$ all decay exponentially at low temperatures and exhibit an abrupt change in behavior at high temperatures $T/T_c \gtrsim 0.5$. By measuring the rates of thermally activated vortex motion (creep) $S(T,H)=|d \ln M(T,H) / d \ln t|$, we reveal glassy behavior involving collective creep of bundles of 2D pancake vortices as well as temperature- and time-tuned crossovers from elastic (collective) dynamics to plastic flow. Based on the creep results, we show that the second magnetization peak coincides with the elastic-to-plastic crossover at low $T$, yet the mechanism changes at higher temperatures.