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

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.