Metal-insulator quantum critical point beneath the high Tc superconducting dome

TL;DR

This study uncovers a quantum critical point beneath the superconducting dome in underdoped YBa2Cu3O6+x, where the quasiparticle effective mass diverges, suggesting a link between quantum criticality and high-temperature superconductivity.

Contribution

It provides experimental evidence for a metal-insulator quantum critical point beneath the superconducting dome, supporting theories of quantum criticality influencing high Tc superconductivity.

Findings

Doping-dependent effective mass upturn near the critical point

Quantum oscillation measurements reveal a divergence in quasiparticle effective mass

Evidence suggests two intersecting superconducting subdomes centered at Fermi surface instabilities

Abstract

An enduring question in correlated systems concerns whether superconductivity is favoured at a quantum critical point (QCP) characterised by a divergent quasiparticle effective mass. Despite such a scenario being widely postulated in high Tc cuprates and invoked to explain non-Fermi liquid transport signatures, experimental evidence is lacking for a critical divergence under the superconducting dome. We use ultra-strong magnetic fields to measure quantum oscillations in underdoped YBa2Cu3O6+x, revealing a dramatic doping-dependent upturn in quasiparticle effective mass at a critical metal-insulator transition beneath the superconducting dome. Given the location of this QCP under a plateau in Tc in addition to a postulated QCP at optimal doping, we discuss the intriguing possibility of two intersecting superconducting subdomes, each centred at a critical Fermi surface instability.