PHYSICAL REVIEW B 99, 104515 (2019) Josephson-like dynamics of the superconducting LaAlO 3 /SrTiO 3 interface S. Hurand, 1, 2 A. Jouan, 1, 2 E. Lesne, 3 G. Singh, 1, 2 C. Feuillet-Palma, 1, 2 M. Bibes, 3 A. Barthélémy, 3 J. Lesueur, 1, 2 and N. Bergeal 1, 2 , * 1 Laboratoire de Physique et d’Etude des Matériaux, ESPCI Paris, PSL Research University, CNRS, 10 Rue Vauquelin – 75005 Paris, France 2 Université Pierre and Marie Curie, Sorbonne-Universités, 75005 Paris, France 3 Unité Mixte de Physique CNRS-Thales, 1 Av. A. Fresnel, 91767 Palaiseau, France (Received 7 December 2017; revised manuscript received 8 February 2019; published 19 March 2019) In this article, we show that the two-dimensional electron gas formed at the LaAlO 3 /SrTiO 3 interface behaves as a Josephson junction array. In particular, it exhibits a stochastic switching of the superconducting critical current, which qualitatively follows the dynamics of the resistively and capacitively shunted Josephson junction model. The switching current distribution (SCD) has been measured as a function of temperature and back- gate voltage. At low temperatures a clear saturation of the standard deviation of the SCD is observed, possibly indicating the presence of a macroscopic quantum tunneling regime with phase diffusion. Through the gate voltage we modify the damping of the array and compare it to artificial arrays of junctions. DOI: 10.1103/PhysRevB.99.104515 I. INTRODUCTION In SrTiO 3 -based heterostructures, such as LaAlO 3 /SrTiO 3 or LaTiO 3 /SrTiO 3 , a high-mobility two-dimensional electron gas (2-DEG) forms at the interface between two insulating layers [1,2]. This electronic system has stimulated intense research efforts due to its exotic properties, which include, in particular, superconductivity [3] in the presence of strong Rashba spin-orbit coupling [4–7]. The interest for oxide in- terfaces is further enhanced by the possibility of modulating the 2-DEG electronic properties by electrostatically tuning the carrier density with a back-gate [8–10] or a top-gate voltage [11–13]. A superconducting phase diagram of the interface can therefore be drawn by plotting the critical tem- perature T c as a function of gate voltage or, equivalently, the carrier density [10,12,14]. Because of the two-dimensional nature of the electron gas, the superconducting transition is expected to belong to the Berezinskii-Kosterlitz-Thouless type of phase transitions [3,15] that is derived within the XY equilibrium model. Consistently, it was shown that the mag- netic field-driven superconductor-to-insulator quantum phase transition in LaTiO 3 /SrTiO 3 interfaces falls into the (2D+1) XY universality class [16]. However, the exact nature of the superconducting phase and its evolution with electrostatic gating remain unclear. In particular, many experiments pro- vide clear evidence of the presence of spatial inhomogeneities whose origin could be related to structural domains or to an intrinsic electronic phase separation [17–22]. Such disorder has important consequences regarding the superconducting properties of oxide interfaces, including a suppression of the superfluid stiffness by phase fluctuations [23]. In this article, we show that the superconducting 2-DEG at the LaAlO 3 /SrTiO 3 interface exhibits the dynamical prop- * Corresponding author: nicolas.bergeal@espci.fr erties of a Josephson-junction (JJ) array that is known to be a physical realization of the 2D XY model. In particular, the critical current switching distribution is qualitatively de- scribed by the resistively and capacitively shunted junction (RCSJ) model whose dynamics can be superimposed on the equilibrium XY model. We also find that the behavior of the LaAlO 3 /SrTiO 3 interface is comparable to that of artificial JJ arrays fabricated with lumped elements. II. EXPERIMENTAL We measured 10-μm-wide and 30-μm-long Hall bars de- fined by the amorphous LaAlO 3 template method [24] in a six-unit-cell-thick LaAlO 3 crystalline layer grown on TiO 2 - terminated SrTiO 3 single crystal by pulsed laser deposition [12]. A metallic gate was deposited on the back side of the 0.5-mm-thick SrTiO 3 substrate. The sample was thermally anchored to the mixing chamber of a dilution refrigerator. In addition to room temperature filtering, low-pass filters were placed at the lowest temperature stage to suppress high-frequency electromagnetic noise and to ensure that the electronic temperature is identical to that of the phonon bath. III. RESULTS Switching and hysteresis. Figure 1 shows the sheet resis- tance of the Hall bar as a function of temperature. A gate- tunable superconducting transition is observed, as already reported for the LaAlO 3 /SrTiO 3 oxide interfaces [10,14]. The critical temperature T c displays a domelike shape as a function of gate voltage with a maximum value of 300 mK for V G =−5 V. While nonhysteretic behavior is usually expected for a homogeneous superconductor, the current-voltage (I - V ) characteristics of the Hall bar show a strong hysteresis [Fig. 2(a)] that is most commonly encountered in JJ [25], 2469-9950/2019/99(10)/104515(6) 104515-1 ©2019 American Physical Society