Quantum critical behaviour in the superfluid density of strongly underdoped ultrathin cuprate films

TL;DR

This study investigates the quantum critical behavior of superfluid density in ultrathin cuprate films, revealing a scaling law near the critical doping level where superconductivity vanishes, highlighting quantum fluctuations as the key factor.

Contribution

It provides experimental evidence of quantum criticality in ultrathin cuprate films, linking superfluid density and transition temperature near the underdoped regime.

Findings

Observation of 2D Kosterlitz-Thouless transition at T_C

Scaling of T_C with superfluid density n_S(0)

Superconductivity loss driven by quantum fluctuations near a 2D quantum critical point

Abstract

A central issue in the physics of high temperature superconductors is to understand superconductivity within a single copper-oxide layer or bilayer, the fundamental structural unit in the cuprates, and how it is lost with underdoping. As mobile holes are removed from the CuO_2 planes, the transition temperature T_C and superfluid density n_S decrease in a surprisingly correlated fashion in crystals and thick films. We seek to elucidate the intrinsic physics of bilayers in the strongly underdoped regime, near the critical doping level where superconductivity disappears. We report measurements of n_S(T) in films of Y_{1-x}Ca_xBa_2Cu_3O_{7-\delta} as thin as two copper-oxide bilayers with T_C's as low as 3 K. In addition to seeing the two-dimensional (2D) Kosterlitz-Thouless-Berezinski transition at T_C, we observe a remarkable scaling of T_C with n_S(0) that demonstrates that the disappearance of superconductivity with underdoping is due to quantum fluctuations near a T = 0 2D quantum critical point.