Ferroelectric Order and Enhanced Interfacial Superconductivity in Lightly-Doped Quantum Paraelectric KTa$_{1-x}$Nb$_x$O$_3$

TL;DR

This paper presents a theoretical analysis showing that Nb doping induces ferroelectric order and enhances interfacial superconductivity in KTaO$_3$, with predictions aligning with experiments and suggesting new ways to engineer quantum phases.

Contribution

It introduces a first-principles-inspired model linking ferroelectric quantum criticality to superconductivity enhancement in doped KTaO$_3$.

Findings

Doped Nb induces long-range ferroelectric order.

Dielectric properties match experimental data across temperature range.

Superconductivity is predicted to be enhanced on (111) surface near quantum-critical doping.

Abstract

Ferroelectric quantum criticality in perovskite oxides offers a fertile ground for emergent collective phenomena. Here we develop a first-principles-inspired quantum-statistics-based theoretical analysis of the ferroelectric order and interfacial superconductivity in lightly-doped quantum paraelectric, niobium (Nb)-doped KTaO$_3$. We demonstrate that local distortions induced by the doped Nb atoms beyond its quantum critical composition induce a long-range ferroelectric order. The predicted dielectric properties quantitatively agree with the experimental measurements over the entire temperature range from the symmetry-broken ferroelectric phase across the phase transition to the paraelectric region. As the same soft phonon mode that governs dielectric behavior provides the essential pairing channel for interfacial superconductivity of KTaO$_3$, we predict a pronounced enhancement of this superconductivity on (111) surface when the system is tuned to its quantum-critical composition via Nb doping, providing a concrete avenue for experimental verification. This finding establishes ferroelectric quantum criticality as a unique design principle for engineering enhanced superconductivity and discovering emergent quantum phases in polar oxide heterostructures, explicitly suggesting that similar materials-tuning strategies (e.g., epitaxial strain) could be exploited to enhance superconductivity in quantum paraelectric systems.