Multiple Quantum Phase Transitions at the superconducting LaTiO3/SrTiO3 interface

TL;DR

This paper investigates multiple quantum phase transitions in superconducting LaTiO3/SrTiO3 interfaces, revealing their universality class, the role of disorder, and the influence of gate-tuned conductance on the nature of the transitions.

Contribution

It provides a detailed analysis of the quantum phase transitions at the interface, identifying their universality class and the conditions leading to single or double transitions based on disorder and coherence length.

Findings

QPT belongs to (2+1)D XY universality class

Transition type depends on 2DEG conductance and disorder

Critical exponents indicate 'clean' or 'dirty' regimes

Abstract

We study the magnetic field driven Quantum Phase Transition (QPT) in electrostatically gated superconducting LaTiO3/SrTiO3 interfaces. Through finite size scaling analysis, we show that it belongs to the (2+1)D XY model universality class. The system can be described as a disordered array of superconducting islands coupled by a two dimensional electron gas (2DEG). Depending on the 2DEG conductance tuned by the gate voltage, the QPT is single (corresponding to the long range phase coherence in the whole array) or double (one related to local phase coherence, the other one to the array). By retrieving the coherence length critical exponent \nu, we show that the QPT can be "clean" or "dirty" according to the Harris criteria, depending on whether the phase coherence length is smaller or larger than the island size. The overall behaviour is well described by a theoretical approach of Spivak et al., in the framework of the fermionic scenario of 2D superconducting QPT.