Direct visualization of local interaction forces in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ vortex matter

TL;DR

This study visualizes and quantifies local vortex-vortex interaction forces in irradiated Bi2212 superconductors, revealing how these forces and pinning vary with magnetic field and defect type, providing insights into vortex matter behavior.

Contribution

It introduces a method to directly measure local interaction forces in vortex matter and compares effects of different defect types on these forces.

Findings

Interaction force magnitude grows with magnetic field.

Irradiated samples have 20-50% smaller pinning forces than defected samples.

Vortex structures are in equilibrium at the measured temperature.

Abstract

We study the local vortex-vortex interaction force $\textbf{f}_i$ of the structure frozen during a field-cooling process in an electron-irradiated Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ sample. We compute this magnitude from snapshots of the vortex structure obtained via magnetic decoration experiments at various fields H in the same sample. Since the observed structures correspond to the equilibrium ones frozen at T$\sim$T$_{irr}$(H), at this temperature the local modulus of $\textbf{f}_i$ roughly equals the local pinning force at the decorated surface of the sample. We estimate the most probable local pinning force from the mode value of the f$_i$(r) distribution, f $_{p}^{m}$. We found that f $_{p}^{m}$ grows algebraically with H and in electron-irradiated samples is 50-20% smaller than for samples with columnar defects.