Pressure induced enhancement of polar distortions in a metal, and implications on the Rashba spin-splitting

TL;DR

This study reveals that applying high pressure enhances polar distortions in the polar metal Ca$_3$Ru$_2$O$_7$, with implications for Rashba spin-splitting and multifunctional device development.

Contribution

It demonstrates pressure-induced enhancement of polar distortions in a polar metal and challenges assumptions about their relationship with Rashba spin-splitting.

Findings

Polar distortions increase under high pressure.

Naive linear assumptions about polar distortion and Rashba splitting are invalid.

DFT calculations provide insights into the complex relationship.

Abstract

Polar metals are an intriguing class of materials in which electric polarisation and metallicity can coexist within a single phase. The unique properties of polar metals challenge expectations, making way for the exploration of exotic phenomena such as unconventional magnetism, hyperferroelectric multiferroicity and developing multifunctional devices that can leverage both the materials electric polarization and its asymmetry in the spin conductivity, that arises due to the Rashba effect. Here, via a high pressure single crystal diffraction study, we report the pressure-induced enhancement of polar distortions in such a metal, Ca$_3$Ru$_2$O$_7$. Our DFT calculations highlight that naive assumptions about the linear dependency between polar distortion amplitudes and the magnitude of the Rashba spin splitting may not be generally valid.