Breaking of the weak-coupling mechanism in polar metals*

Polar metals exist because polar atomic displacements and metallicity can harmoniously coexist if inversion symmetry is removed through displacements of atoms whose electronic degrees of freedom are decoupled from the states at the Fermi level [1]."

For ABO₃ and A_n+1B_nO_3n+1 layered Ruddlesden-Popper perovskite structures with n=2, this weak-coupling ansatz leads to the operational principle that the polar distortions and electronic properties originate from two different sublattices.

Here we rationally design a polar metal oxide, utilizing oxygen vacancy ordering, which circumvents the weak-coupling principle. Experimental observations and first-principles calculations are used to support our design strategy.

1. D. Puggioni and J. M. Rondinelli, Nature Communications 5, 3432 (2014)