Origin of the metal-to-insulator crossover in cuprate superconductors

TL;DR

This paper investigates the metal-to-insulator crossover in cuprate superconductors, attributing it to a drop in carrier density linked to the pseudogap phase, supported by high-field resistivity and Hall measurements across multiple compounds.

Contribution

It proposes a universal mechanism where the crossover is caused by a carrier density reduction at the pseudogap onset, supported by quantitative resistivity and Hall data.

Findings

Resistivity upturns are consistent with a carrier density drop from 1+p to p.

The mechanism explains resistivity behavior in LSCO, YBCO, and Nd-LSCO.

The carrier density drop is approximately 1 hole per Cu atom.

Abstract

Superconductivity in cuprates peaks in the doping regime between a metal at high p and an insulator at low p. Understanding how the material evolves from metal to insulator is a fundamental and open question. Early studies in high magnetic fields revealed that below some critical doping an insulator-like upturn appears in the resistivity of cuprates at low temperature, but its origin has remained a puzzle. Here we propose that this 'metal-to-insulator crossover' is due to a drop in carrier density n associated with the onset of the pseudogap phase at a critical doping p*. We use high-field resistivity measurements on LSCO to show that the upturns are quantitatively consistent with a drop from n=1+p above p* to n=p below p*, in agreement with high-field Hall data in YBCO. We demonstrate how previously reported upturns in the resistivity of LSCO, YBCO and Nd-LSCO are explained by the same universal mechanism: a drop in carrier density by 1.0 hole per Cu atom.