Glassy Dynamics in a heavy ion irradiated NbSe2 crystal

TL;DR

This study investigates vortex-glass behavior in a NbSe2 crystal with tilted columnar defects, revealing glassy states and disorder effects, but not the characteristic peaks seen in other materials like YBCO.

Contribution

It demonstrates the impact of tilted columnar defects on vortex dynamics in NbSe2, expanding understanding of glassy phases beyond YBCO and exploring disorder-induced transitions.

Findings

Magnetization is five times higher with defects parallel to the field.

Vortex motion rate S is minimized when field aligns with defects.

No peak in S(T) or plateau observed as in YBCO.

Abstract

Fascination with glassy states has persisted since Fisher introduced the vortex-glass as a new thermodynamic phase that is a true superconductor that lacks conventional long-range order. Though Fisher's original model considered point disorder, it was later predicted that columnar defects (CDs) could also induce glassiness -- specifically, a Bose-glass phase. In YBa$_2$Cu$_3$O$_{7-x}$ (YBCO), glassy states can cause distinct behavior in the temperature ($T$) dependent rate of thermally activated vortex motion ($S$). The vortex-glass state produces a plateau in $S(T)$ whereas a Bose-glass can transition into a state hosting vortex excitations called double-kinks that can expand, creating a large peak in $S(T)$. Although glass phases have been well-studied in YBCO, few studies exist of other materials containing CDs that could contribute to distinguishing universal behavior. Here, we report on the effectiveness of CDs tilted ~30$\deg$ from the c-axis in reducing $S$ in a NbSe$_2$ crystal. The magnetization is 5 times higher and $S$ is minimized when the field is parallel to the defects versus aligned with the c-axis. We see signatures of glassiness in both field orientations, but do not observe a peak in $S(T)$ nor a plateau at values observed in YBCO. We discuss the possibility that competing disorder induces a field-orientation-driven transition from a Bose-glass to an anisotropic glass involving both point and columnar disorder.