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

We investigated the nature of the quasiparticle 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, Bi2Sr2CaCu2Oy and YBa2Cu3Oy 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.

Automated summary

The Hall angle of the vortex motion in cuprates was found to be independent of the magnetic field in BSCCO, reaching unity at low temperatures, while in YBCO, the angle increased with increasing magnetic field even at low temperatures. The difference in the magnetic field dependence of the Hall angle was attributed to the varying influence of pinning originating from differences in the vortex state between the two materials. Both materials exhibited a significantly large tangent of the Hall angle at low temperatures, suggesting possible nonlinearity in viscous drag force and hidden dissipation mechanisms. The unexpectedly large Hall angle observed in the flux-flow Hall effect study raises fundamental questions regarding the motion of quantized vortices in superconductors, warranting further investigation.