Insulating transition in the flux-flow resistivity of a high temperature superconductor

TL;DR

This study reveals a metal-insulator transition in the flux-flow resistivity of optimally doped YBa2Cu3O6+x superconductors at low temperatures, observed through high-resolution microwave measurements, indicating intrinsic electronic phase changes within vortex cores.

Contribution

First to report a metal-insulator transition in optimally doped YBa2Cu3O6+x, using microwave flux-flow resistivity measurements in the mixed state at very low temperatures.

Findings

Metal-insulator transition observed at 13 K

Logarithmic resistivity growth below 5 K

Transition occurs in high-quality samples at low magnetic fields

Abstract

Measurements of the DC resistivity of under-doped cuprate superconductors have revealed a metal--insulator transition at low temperatures when superconductivity is suppressed by a very large magnetic field, with the resistivity growing logarithmically in the low temperature limit. This insulating behaviour has been associated not only with the large magnetic fields, but also with the under-doped composition and intrinsic sample inhomogeneity, and it is important to establish whether these factors are essential to it. Here we report high resolution microwave measurements of the flux-flow resistivity of optimally doped YBa_(2)Cu_(3)O_(6+x) in the mixed state at temperatures down to 1.2 K. We find that the effective resistivity of the vortex cores exhibits a metal-insulator transition, with a minimum at 13 K and a logarithmically growing form below 5 K. The transition is seen in samples of the highest quality and in magnetic fields as low as 1 T. Our work is the first report of a metal-insulator transition in optimally doped YBa_(2)Cu_(3)O_(6+x), and the first such transition to be seen in a system in which superconductivity has not been globally suppressed.