High-temperature superconductivity at the lanthanum cuprate/lanthanum–strontium nickelate interface

Abstract

The utilization of interface effects in epitaxial systems at the nanoscale has emerged as a very powerful approach for engineering functional properties of oxides. Here we present a novel structure fabricated by a state-of-the-art oxide molecular beam epitaxy method and consisting of lanthanum cuprate and strontium (Sr)-doped lanthanum nickelate, in which interfacial high-temperature superconductivity (Tc up to 40 K) occurs at the contact between the two phases. In such a system, we are able to tune the superconducting properties simply by changing the structural parameters. By employing electron spectroscopy and microscopy combined with dedicated conductivity measurements, we show that decoupling occurs between the electronic charge carrier and the cation (Sr) concentration profiles at the interface and that a hole accumulation layer forms, which dictates the resulting superconducting properties. Such effects are rationalized in the light of a generalized space-charge theory for oxide systems that takes account of both ionic and electronic redistribution effects.

Design of Complex Oxide Interfaces by Oxide Molecular Beam Epitaxy

“…In particular, although the LCO (bottom)-LSNO (top) interface is found to be sharp, an obvious Sr redistribution in the LCO phase in growth direction is detected, which slightly changes depending on the doping level in the LSNO layer. The details are discussed in Ref [112]. Lastly, the broad resistance transition to the superconducting state at such high-onset temperature (similar to optimum-doped LSCO) and the reduced Meissner effect should also be pointed out, since this is an indirect evidence of the inhomogeneous superconducting interface with nanoscale superconducting puddles as a consequence of the interface intermixing.…”

“…One recent example of hetero-interface engineering by oxide MBE is the HT-IS with a critical temperature up to T c ≈ 40 K at LCO-La 2−x Sr x NiO 4 (LSNO) multilayers (Fig. 6a) [112]. Note that LCO and LSNO compounds share the same Ruddlesden-Popper 214-crystal structure, and the electronic phase transformation can be achieved by hole-carriers doping by the substitution of the La site with a Sr dopant.…”

Engineering mass transport properties in oxide ionic and mixed ionic-electronic thin film ceramic conductors for energy applications

“…due to concentration of vacancies, defect segregation, cationic and anionic inter-diffusion, Figure 3c). [70,92,125,126] As a consequence, a local redistribution of all the mobile (ionic and electronic) defects is expected in conditions of thermodynamic equilibrium (i.e. constancy of the electrochemical potential for each defect specie) within the so-called space-charge region across the interface, as described by Poisson-Boltzmann equation: [11]…”

High-temperature interface superconductivity in bilayer copper oxide films by pulsed laser deposition

“…The effect of interface on superconductivity has received much attention. It was demonstrated that superconductivity can occur at the interface of two nonsuperconducting materials [1][2][3][4][5][6], and the critical temperature (T c ) can even be significantly enhanced com-pared with the corresponding single-phase samples [1,[7][8][9]. One of the most intriguing interfaces is the bilayer of La 2 CuO 4 and La 2−x Sr x CuO 4 [LSCO(x)] films.…”

“…The lacking of relevant studies might be in part because the heavily Sr-riched LSCO(x) films are not stable due to oxygen vacancies [13,16]. In previous studies [1,[5][6][7]11] of interface superconductivity, the bilayers were grown in a unique atomic-layer-by-layer molecular beam epitaxy (MBE) system that was fantastic in making atomically flat high-quality samples, but might not be suitable in making the heavily Sr-riched LSCO(x) films. In contrast, due to its thermodynamically nonequilibrium nature, pulsed laser deposition (PLD) can be used to produce metastable films far from chemical equilibrium [17].…”