Multiple quantum criticality in a two-dimensional superconductor

• Published in: Nature materials Vol. 12; no. 6; pp. 542 - 548
• Main Authors: Biscaras, J., Bergeal, N., Hurand, S., Feuillet-Palma, C., Rastogi, A., Budhani, R. C., Grilli, M., Caprara, S., Lesueur, J.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-06-2013; Nature Publishing Group
• Subjects: 639/301/119/1003; Arrays; Biomaterials; Coherence length; Condensed Matter Physics; Conductance; Magnetic fields; Magnetism; Materials Science; Mathematical models; Nanotechnology; Optical and Electronic Materials; Phase coherence; Quantum physics; Superconductivity; Superconductors; Two dimensional
• ISSN: 1476-1122; 1476-4660
• DOI: 10.1038/nmat3624

The diverse phenomena associated with the two-dimensional electron gas (2DEG) that occurs at oxide interfaces include, among others, exceptional carrier mobilities, magnetism and superconductivity. Although these have mostly been the focus of interest for potential future applications, they also offer an opportunity for studying more fundamental quantum many-body effects. Here, we examine the magnetic-field-driven quantum phase transition that occurs in electrostatically gated superconducting LaTiO
3
/SrTiO
3
interfaces. Through a finite-size scaling analysis, we show that it belongs to the (2+1)D
X
Y
model universality class. The system can be described as a disordered array of superconducting puddles coupled by a 2DEG and, depending on its conductance, the observed critical behaviour 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). A phase diagram illustrating the dependence of the critical field on the 2DEG conductance is constructed, and shown to agree with theoretical proposals. Moreover, by retrieving the coherence-length critical exponent
ν
, we show that the quantum critical behaviour can be clean or dirty according to the Harris criterion, depending on whether the phase-coherence length is smaller or larger than the size of the puddles.
The range of phenomena associated with the two-dimensional electron gas occurring at oxide interfaces has garnered significant attention. By performing a finite-size scaling analysis, the universality class of the magnetic field-driven quantum phase transition that occurs at the superconducting LaTiO
3
/SrTiO
3
interface is now established.