Strongly coupled interface ferroelectricity and interface superconductivity in LAO/KTO

TL;DR

This study uncovers the coexistence of ferroelectricity and superconductivity at the LAO/KTO interface, demonstrating that ferroelectric manipulation can drastically alter interfacial conductivity and superconducting properties, revealing new physics and potential device applications.

Contribution

It provides the first experimental evidence of ferroelectricity at the LAO/KTO interface and shows its strong coupling with superconductivity, enabling non-volatile control of interfacial quantum states.

Findings

Ferroelectric order confirmed by STEM, SHG, and PFM.

Manipulating ferroelectricity changes interfacial conductivity by over 1000 times.

Superconductivity can be suppressed and reentrant due to ferroelectric polarization switching.

Abstract

Interfaces can differ from their parent compounds in terms of charge, spin, and orbital orders and are fertile ground for emergent phenomena, strongly correlated physics, and device applications. Here, we discover that ferroelectric order resides at the interface of two oxides, LaAlO3/KTaO3(111) (LAO/KTO), where two seemingly mutually exclusive orders-ferroelectricity and superconductivity-coexist. Moreover, manipulating ferroelectricity can change the interfacial conductivity by more than 1000 times, simultaneously causing superconductivity to diminish and reappear due to the coupling between these phenomena. The ferroelectricity is confirmed by scanning transmission electron microscopy (STEM), second harmonic generation (SHG) microscopy, and piezoelectric force microscopy (PFM). STEM reveals K ions are displaced relative to Ta ions, with the help of oxygen vacancies at the LAO/KTO interface. The resultant electric polarization is locally switchable by applying a voltage between the PFM tip and the LAO film. The ferroelectric hysteresis correlates with hysteresis change in interfacial conductivity and the superconducting transition temperature (Tc). The loss and reentrance of superconductivity are accounted for by orders of magnitude change in the Hall mobility induced by the polarization switching. These findings open the door to ferroelectric superconductivity with broken inversion symmetry and non-volatile modulation of superconductivity.