Double criticality in the magnetic field-driven transition of a high-TC superconductor

TL;DR

This paper provides experimental evidence for two distinct quantum critical regimes in underdoped La2-xSrxCuO4 thin films under high magnetic fields, revealing complex transitions in high-TC superconductors.

Contribution

It identifies and characterizes two separate quantum critical points in a high-TC superconductor under magnetic fields, highlighting different critical behaviors and regimes.

Findings

Observation of a 'ghost' QCP with fermionic critical exponents at 18-20T

Detection of a second QCP around 37T indicating a dimensional or disorder crossover

Evidence of complex quantum critical behavior in high-TC cuprate superconductors.

Abstract

Driving a two-dimensional superconductor normal by applying a high magnetic field may lead to Cooper pair localization. In this case, there should be a quantum critical point associated with specific scaling laws. Such a transition has been evidenced in a number of low critical temperature superconducting thin films and has been suggested to occur also in high temperature cuprate superconductors. Here we show experimental evidence for two distinct quantum critical regimes when applying perpendicular magnetic fields to underdoped La2-xSrxCuO4 thin films. At intermediate values of the magnetic field (18T-20T), a "ghost" QCP is observed, for which the values of the related critical exponents point towards a fermionic -as opposed to bosonic- scenario. At higher (about 37 T) magnetic field, another QCP is observed, which suggests the existence of either a 2D/3D or a clean/dirty temperature crossover.