Multiple quantum criticality in a two-dimensional superconductor

Abstract

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 LaTiO3/SrTiO3 interfaces. Through a 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 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.

Inhomogeneous multi carrier superconductivity at LaXO3/SrTiO3(X = Al or Ti) oxide interfaces

“…VII, we provide further evidence for inhomogeneous superconductivity at oxide interfaces, coming from the peculiar multiple quantum critical scaling, observed when superconductivity is suppressed by means of a magnetic field, revisiting the results of Ref. [21]. In Sec.…”

“…4,12,15,16,21,22 Here, we first provide new compelling evidence of the inhomogeneous character of the 2DEG, extending previous multicarrier analyses of magneto-transport measurements to deal with inhomogeneous systems. We then put together the various pieces of the jigsaw into an overall coherent theoretical framework.…”

“…The electrode measures several hundreds µm across, thus being orders of magnitude larger than the nanoscale inhomogeneities. 21 At the lowest measured temperature, T = 30 mK, the spectra reveal a gap in the DOS at the Fermi energy, over the entire range of explored gate voltages V g ∈ [−300, 300] V, accompanied by more or less broadened coherence peaks above the gap, pointing to superconducting coherence and pairing as the origin of DOS suppression [see Fig. 4(h)].…”

Interface superconductivity

“…This interesting system presents many similarities with the LAO/STO compound. A detailed account of experiments performed on this heterostructure, mostly in Jérôme Lesueur's group in Paris, can be found in references [78,79].…”

Phase Separation from Electron Confinement at Oxide Interfaces

“…Here the electrostatic potential confining the electron gas at the interface is calculated self-consistently, finding that the electron confinement at the interface may induce phase separation, to avoid a thermodynamically unstable state with a negative compressibility. This provides a generic robust and intrinsic mechanism for the experimentally observed inhomogeneous character of these interfaces.PACS numbers: 73.43.Nq,73.21.Fg, The two-dimensional electron gas (2DEG) that forms at the interface of two insulating oxides, like LaAlO 3 /SrTiO 3 and LaTiO 3 /SrTiO 3 (hereafter generically referred to as LXO/STO) [1][2][3][4], exhibits a rich phenomenology, such as a gate-tunable metal-tosuperconductor transition [5][6][7][8], a magnetic-field-tuned quantum criticality [9], and inhomogeneous magnetic responses [10][11][12][13][14][15]. Tunneling [16,17] and SQUID magnetometry [18] provide clear evidence of an inhomogeneous interface on both micro-and nanoscopic scales.…”