# Emergent superconductivity in single crystalline $\mathrm{MgTi}_2\mathrm{O}_4$ films via structural engineering

## TL;DR

This paper reports the discovery of superconductivity in MgTi2O4 spinel films engineered as superlattices with SrTiO3, revealing tunable transition temperatures and unconventional critical field behavior, expanding the potential of spinel compounds for superconductivity.

## Contribution

It demonstrates emergent superconductivity in MgTi2O4 via structural engineering, showing control over transition temperature and critical fields, and elucidates its origin through electronic structure analysis.

## Key findings

- Superconductivity achieved in MgTi2O4 films with T_c up to 5 K.
- Superlattice exhibits isotropic upper critical field exceeding Pauli limit.
- Superconductivity linked to suppression of Ti-Ti dimerization.

## Abstract

Spinel compounds have demonstrated rich functionalities but rarely shown superconductivity. Here, we report the emergence of superconductivity in the spinel $\mathrm{MgTi}_2\mathrm{O}_4$, known to be an insulator with a complicated order. The superconducting transition is achieved by engineering a superlattice of $\mathrm{MgTi}_2\mathrm{O}_4$ and $\mathrm{SrTiO}_3$. The onset transition temperature in the $\mathrm{MgTi}_2\mathrm{O}_4$ layer can be tuned from 0 to 5 K in such geometry, concurrently with a stretched $c$-axis (from 8.51 to 8.53 \AA) compared to the bulk material. Such a positive correlation without saturation suggests ample room for the further enhancement. Intriguingly, the superlattice exhibits isotropic upper critical field $H_{\mathrm{c}2}$ that breaks the Pauli limit, distinct from the highly anisotropic feature of interface superconductivity. The origin of superconductivity in the $\mathrm{MgTi}_2\mathrm{O}_4$ layer is understood in combination with the electron energy loss spectra and the first-principles electronic structure calculations, which point to the birth of superconductivity in the $\mathrm{MgTi}_2\mathrm{O}_4$ layer by preventing the Ti-Ti dimerization. Our discovery not only provides a platform to explore the interplay between the superconductivity and other exotic states, but also opens a new window to realize superconductivity in the spinel compounds as well as other titanium oxides.