Metal-to-Insulator Crossover in YBa_{2}Cu_{3}O_{y} Probed by Low-Temperature Quasiparticle Heat Transport

TL;DR

This study investigates the magnetic-field dependence of low-temperature thermal conductivity in YBa2Cu3O7−y across various doping levels, revealing a metal-insulator crossover at a critical doping of about 0.07 holes per Cu, linked to stripe correlations.

Contribution

It extends the understanding of metal-insulator crossover in cuprates by measuring thermal conductivity in YBCO and identifying a critical doping deep in the underdoped regime.

Findings

Critical doping for crossover is around 0.07 holes/Cu.

Thermal conductivity behavior indicates a ground state change.

Stripe correlations are associated with the crossover.

Abstract

It was recently demonstrated that in La_{2-x}Sr_{x}CuO_{4} the magnetic-field (H) dependence of the low-temperature thermal conductivity \kappa up to 16 T reflects whether the normal state is a metal or an insulator. We measure the H dependence of \kappa in YBa_{2}Cu_{3}O_{y} (YBCO) at subkelvin temperatures for a wide doping range, and find that at low doping the \kappa(H) behavior signifies the change in the ground state in this system as well. Surprisingly, the critical doping is found to be located deeply inside the underdoped region, about the hole doping of 0.07 hole/Cu; this critical doping is apparently related to the stripe correlations as revealed by the in-plane resistivity anisotropy.