Fabrication of High-Temperature Quasi-Two-Dimensional Superconductors at the Interface of a Ferroelectric ${\mathrm{Ba}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{TiO}}_3$ Film and an Insulating Parent Compound of ${\mathrm{La}}_2{\mathrm{CuO}}_4$

We report the first observation of superconductivity in a heterostructure consisting of an insulating ferroelectric film (${\mathrm{Ba}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{TiO}}_3$) grown on an insulating parent compound of ${\mathrm{La}}_2{\mathrm{CuO}}_4$ with [001] orientation. The heterostructure was prepared by magnetron sputtering on a nonatomically flat surface with inhomogeneities of the order of 1–2 nm. The measured superconducting transition temperature $T_c$ is about 30 K. We have shown that superconductivity is confined near the interface region. Application of a weak magnetic field perpendicular to the interface leads to the appearance of the finite resistance. That confirms the quasi-two-dimensional nature of the superconductive state. The proposed concept promises ferroelectrically controlled interface superconductivity which offers the possibility of novel design of electronic devices.

Figure 1

The schematic structures of ${\mathrm{Ba}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{TiO}}_3/{\mathrm{La}}_2{\mathrm{CuO}}_4$ (a) with Q2DEG (shown in red); AFM image of the ${\mathrm{La}}_2{\mathrm{CuO}}_4$ single crystal surface without the film (b) illustrates the inhomogeneity of the interface. The temperature dependence of the magnetic susceptibility (c), and the temperature dependence of the resistivity (d) of ${\mathrm{La}}_2{\mathrm{CuO}}_4$ single crystal (without ferroelectric film).

Figure 2

The temperature dependence of the resistance of ${\mathrm{Ba}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{TiO}}_3/{\mathrm{La}}_2{\mathrm{CuO}}_4$ heterostructure in the wide temperature range (a) and at low temperatures (b) (the results of the same measurements).

Figure 3

The magnetic field dependence of the resistance of the ${\mathrm{Ba}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{TiO}}_3/{\mathrm{La}}_2{\mathrm{CuO}}_4$ heterostructure.

Figure 4

The temperature dependence of the resistance of the ${\mathrm{Ba}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{TiO}}_3/{\mathrm{La}}_2{\mathrm{CuO}}_4$ heterostructure from the substrate side. The temperature dependence of the heterostructure resistance is measured by electrodes deposited on the ${\mathrm{La}}_2{\mathrm{CuO}}_4$ surface opposite to the surface with the film.