Coexistence of spontaneous polarization and superconductivity in hole-doped oxyhydrides ATiO(2)H (A = K, Rb, Cs): First-principles study

Abstract

Polar metal is a material that hosts both polar distortion and metallicity. Such a material is expected to show exotic magneto-electric phenomena if it 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 first-principles calculations based on 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 (similar to 100 mu C/cm(2)) originates from the weak coupling of the polar distortion and superconducting states, the reason for which is the separation of the displaced atoms and spatially confined metallic carriers. Additionally, superconductivity is enhanced by the unique electronic properties near the valence band maximum: quartic band dispersion with a sizable contribution of hydrogen 1s states. This paper thus features the oxyhydrides as possible model polar superconducting systems, which may be utilizable for future magneto-electric devices.