R. Ogawa | Searcharxiv

arXiv2023

Microwave flux-flow Hall effect in a multi-band superconductor FeSe

We have measured the flux-flow Hall effect in a multi-band superconductor FeSe pure single crystal to investigate the nature of the vortex core state by means of the cross-shaped bimodal cavity technique. We found that the flux-flow Hall angle of FeSe at low temperatures is about 0.5, which is equal to or smaller than that evaluated by the effective viscous drag coefficient measurements. This feature is in contrast to the cuprate superconductors. The conductivity tensor of multi-band superconductors that are contributed from holes and electrons shows partial cancellation of the flux-flow Hall voltage by the electrons and holes, wchich can explain the observed feature. Therefore, our study suggests the appearance of the multi-band nature in the vortex dynamics.

cond-mat.supr-con↗

arXiv2021

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

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.

cond-mat.supr-con↗