Electric octupole order in bilayer Rashba system

TL;DR

This paper investigates the emergence of electric octupole order in bilayer Rashba systems, highlighting the role of spin-orbit coupling and symmetry, with implications for high-temperature superconductors.

Contribution

It introduces a mechanism for stabilizing electric octupole order via layer-dependent Rashba spin-orbit coupling in bilayer systems.

Findings

Electric octupole order is stabilized by Rashba spin-orbit coupling.

The spin texture and magnetic response are characterized.

A parity-breaking quantum critical point is identified under magnetic field.

Abstract

The odd-parity multipole is an emergent degree of freedom, leading to spontaneous inversion symmetry breaking. The odd-parity multipole order may occur by forming staggered even-parity multipoles in a unit cell. We focus on a locally noncentrosymmetric bilayer Rashba system, and study an odd-parity electric octupole order caused by the antiferro stacking of local electric quadrupoles. Analyzing the forward scattering model, we show that the electric octupole order is stabilized by a layer-dependent Rashba spin-orbit coupling. The roles of the spin-orbit coupling are clarified on the basis of the analytic formula of multipole susceptibility. The spin texture allowed in the D_2d point group symmetry and its magnetic response are revealed. Furthermore, we show that the parity-breaking quantum critical point appears in the magnetic field. The possible realization of the electric octupole order in bilayer high-T_c cuprate superconductors is discussed.