Large Hall angle of vortex motion in high-$T_c$ cuprate superconductors revealed by microwave flux-flow Hall effect

TL;DR

This study reveals an unexpectedly large Hall angle in vortex motion within high-$T_c$ cuprate superconductors, challenging existing theories and highlighting the influence of vortex state and pinning effects on vortex dynamics.

Contribution

It provides the first detailed measurements of flux-flow Hall effect at microwave frequencies in different cuprate superconductors, uncovering large Hall angles and their dependence on vortex state and pinning.

Findings

Hall angle reaches near unity in BSCCO at low temperatures

Hall angle increases with magnetic field in YBCO due to vortex state differences

Large Hall angles exceed previous estimates from viscous drag measurements

Abstract

We investigated the nature of the quasi-particle state in the vortex core by means of the flux-flow Hall effect measurements at 15.8 GHz. We measured the flux-flow Hall effect in cuprate superconductors, Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{y}$ and YBa$_{2}$Cu$_{3}$O$_{y}$ single crystals, whose equilibrium $B$-$T$ phase diagrams were different. As a result, we found that the Hall angle is independent of the magnetic field, and reaches an order of unity at low temperatures in BSCCO. However, in YBCO, the angle increases with increasing magnetic field even at low temperatures. We understood that this difference in the magnetic field dependence of the Hall angle is due to the difference in the influence of the pinning, which originated from the difference in the vortex state (liquid vs. solid) between the two materials. However, as a common feature, both materials showed a large tangent of the Hall angle at low temperatures, which was larger by an order of magnitude than those obtained in the effective viscous drag coefficient measurements. We discussed the origin of the discrepancy both in terms of the possible nonlinearity of the viscous drag force and possible hidden dissipation mechanisms. The unexpectedly large Hall angle of the vortex motion in cuprates revealed in our flux-flow Hall effect study poses a serious question on the fundamental understanding of the motion of the quantized vortex in superconductors, and it deserves further investigation.