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Two-dimensional electronic gases (2DEGs) in SrTiO3-based heterostructures are known to be superconudcting [1]. In these systems, the critical temperature is tunable with an electrostatic gate voltage [2] that controls the carrier density of the 2DEG. Researchers have observed in this 2DEG density-of-states features resembling the pseudogap in cuprates [3] and paired electronic states without superconductivity [4]. Consequently, it has has emerged as a model system to study the physics of Cooper pair formation in two dimensions.

Our experiments on gate-controlled superconductivity in an AlOx / SrTiO3 heterostructure has revealed some striking similarities between features of the superconducting phase transition and the liquid-gas phase transition described by the van der Waals theory. We have measured non-equilibrium transport properties by measuring the relaxation time to reach steady-state conditions after a perturbation is applied to the electronic system. There are signifanct differences in behaviour above and below the critical superconducting parameters (critical temperature and critical magnetic field). We will discuss these results and its possible connection to the phenomenon of hydrodynamic flow of electron liquids.

[1] Reyren et al., Science 317, 1196 (2007)
[2] Caviglia et al., Nature 456, 624 (2008)
[3] Richter et al., Nature 502, 528 (2013)
[4] Cheng et al., Nature 521, 196 (2015)