Research Update: Conductivity and beyond at the LaAlO3/SrTiO3 interface

Abstract

In this review, we focus on the celebrated interface between two band insulators, LaAlO3 and SrTiO3, that was found to be conducting, superconducting, and to display a strong spin-orbit coupling. We discuss the formation of the 2-dimensional electron liquid at this interface, the particular electronic structure linked to the carrier confinement, the transport properties, and the signatures of magnetism. We then highlight distinctive characteristics of the superconducting regime, such as the electric field effect control of the carrier density, the unique tunability observed in this system, and the role of the electronic subband structure. Finally we compare the behavior of Tc versus 2D doping with the dome-like behavior of the 3D bulk superconductivity observed in doped SrTiO3. This comparison reveals surprising differences when the Tc behavior is analyzed in terms of the 3D carrier density for the interface and the bulk.

Modulation of the superconducting critical temperature due to quantum confinement at the LaAlO3/SrTiO3 interface

“…In Sec. III, we discuss recent experimental data by some of us on the LAO/STO 2DEL thickness [27]. With these data at hand, we can deduce from the measured Hall 2D density an equivalent 3D density for the 2DEL.…”

“…The in-plane coherence length remains larger than the superconducting thickness for all dopings [14,39], which is again consistent with the 2D character of the superconducting 2DEL. Figure 2 displays the thicknesses and critical temperatures measured as a function of the Hall density n 2D [27]. The dependence T c (n 2D ) draws a dome with a maximum at 365 mK.…”

Nonlinear I−V characteristics of two-dimensional superconductors: Berezinskii-Kosterlitz-Thouless physics versus inhomogeneity

“…The most crucial limitation comes from the fact that in clean thick films J s is much larger than the critical temperature, so that the temperature T BKT where J s (T BKT ) T BKT is indistinguishable from the T c at which pairing disappears. In few-nanometer thick films of conventional superconductors, like NbN or MoGe, the BKT scale becomes accessible, thanks to the fact that in such ultrathin films n s (and then J s ) is strongly suppressed by disorder [1,2,[10][11][12][13][14][15][18][19][20]. A similar condition can be reached in STO-based interfaces, where an extremely fragile SC condensate was recently reported [21][22][23].…”

Homogeneous superconductivity at the LaAlO3/SrTiO3 interface probed by nanoscale transport

“…The discovery of a two-dimensional electron system (2DES) at the interface between two wide band-gap insulators, LaAlO 3 (LAO) and SrTiO 3 (STO), that exhibits superconductivity, coexisting with intrinsic ferromagnetism and large gate-tunable spin-orbit coupling (SOC), has stimulated great interest and many experimental and theoretical studies of this system [3,4].…”

“…The thickness of the superconducting layer is also doping-dependent and was estimated from the anisotropy of parallel and perpendicular magnetic fields to be about 10 nm for optimal doping conditions. However, the thickness may extend up to 100 nm in the overdoped regime [4]. Recent theoretical investigations predicted the possibility of multiband superconductivity driven by the two-dimensional character in the LAO/STO interface [10].…”