Evidence for an angular dependent contribution from columnar defects to the equilibrium magnetization of YBa_2Cu_3O_{7-d}

TL;DR

This study investigates how columnar defects in YBa_2Cu_3O_{7-d} influence the equilibrium magnetization, revealing an angle-dependent contribution that affects vortex pinning and is sensitive to temperature and magnetic field conditions.

Contribution

It provides experimental evidence of an angle-dependent contribution from columnar defects to the magnetization, highlighting the role of thermal fluctuations in pinning energy renormalization.

Findings

Observed a jump in equilibrium torque at defect crossing angles.

Pinning energy decreases and vanishes below Tc due to thermal fluctuations.

Quantified the energy gain from vortex pinning on defects.

Abstract

We have measured an angle-dependent contribution to the equilibrium magnetization of a YBa_2Cu_3O_{7-d} single crystal with columnar defects created by 5.8GeV Pb ions. This contribution manifests itself as a jump in the equilibrium torque signal, when the magnetic field crosses that of the defects. The magnitude of the signal, which is observed in a narrow temperature interval less than 2K and for fields up to about twice the irradiation field, is used to estimate the the energy gained by vortex pinning on the defects. The vanishing of the effective pinning energy at a temperature below Tc is attributed to its renormalization by thermal fluctuations.