Coexistence of spontaneous polarization and superconductivity in hole-doped oxyhydrides ATiO_2H (A=K, Rb, Cs): first-principles study

TL;DR

This first-principles study predicts that hole-doped ATiO2H oxyhydrides exhibit coexistence of spontaneous polarization and superconductivity, highlighting their potential for magneto-electric applications.

Contribution

It is the first to demonstrate the coexistence of ferroelectricity and superconductivity in oxyhydrides through detailed theoretical calculations.

Findings

Spontaneous polarization and superconductivity coexist at optimal doping.

Weak coupling between polar distortion and superconducting states.

Enhanced superconductivity due to unique electronic properties near the valence band maximum.

Abstract

The polar metal is a material that hosts both polar distortion and metallicity. Such a material is expected to show exotic magneto-electric phenomena if superconducts. Here, we theoretically explore ferroelectric and superconducting properties in a series of perovskite-type oxyhydrides ATiO$_2$H (A=K, Rb, Cs) under hole-doping conditions using the first-principles calculations based on the density functional theory. Our simulation shows that these compounds host spontaneous polarization and superconductivity at optimal doping concentration. The unusual coexistence of superconductivity and large polarization (~100 ${\mu}$C/cm$^2$) originates from weak coupling of the polar distortion and superconducting states, the reason of which is separation of the displaced atoms and spacially confined metallic carriers. Besides, the superconductivity is enhanced by the unique electronic properties near the valence band maximum: quartic band dispersion with a sizable contribution of hydrogen 1s states. Our study thus feature the oxyhydrides as possible model polar superconducting systems, which may be utilizable for future magneto-electric devices.