Competing orders suppressed by disorder around a hidden quantum critical point in cuprate high Tc superconductors

TL;DR

This study uses muon spin rotation to explore how disorder affects competing magnetic and superconducting orders in lightly doped cuprates, revealing a hidden quantum critical point and the interplay between phases.

Contribution

It provides a detailed 3D phase diagram of lightly doped cuprates, highlighting the role of disorder in suppressing competing orders and unveiling a hidden quantum critical point.

Findings

Disorder suppresses both magnetic and superconducting orders.

A hidden quantum critical point exists beneath a frozen insulating magnetic state.

Doping and disorder induce a first-order phase transition line ending at the critical point.

Abstract

We report extensive muon spin rotation measurements on the lightly doped Y1-xCaxBa2Cu3O6+y compound, which allows us to disentangle the effect of disorder, controlled by random Ca2+ substitution, from that of mere doping. A 3D phase diagram of lightly doped cuprates is accurately drawn, showing that a thermally activated antiferromagnetic phase competes with superconductivity around a quantum critical point, hidden underneath a frozen insulating magnetic state. Disorder suppresses both competing order parameters and unveils the underlying frozen state. Doping and disorder destroy the activated magnetic phase along a line of first order phase transitions that ends at the critical point.