Light-driven octupolar inverse Faraday effect and multipolar order in Mott insulators

Abstract

Hidden multipolar orders in spin-orbit-coupled Mott insulators provide a promising setting for correlated quantum matter, yet their control and detection remain major challenges. Here, we demonstrate that circularly polarized light enables both the control and detection of hidden multipolar order in $4d^2/5d^2$ systems with edge-sharing octahedra. Using a Floquet Schrieffer-Wolff expansion of a driven Hubbard-Kanamori model, we derive a low-energy multipolar Hamiltonian with two qualitatively new light-driven terms. One is an effective static field that couples linearly to the magnetic octupole, realizing an octupolar inverse Faraday effect. The other is a bond-dependent anisotropic exchange interaction absent in equilibrium. These two couplings constitute the key mechanisms of this work: the first provides a direct optical handle on hidden octupolar order, while the second reorganizes the multipolar exchange landscape and introduces strong bond-dependent frustration. Together, these couplings define a nonequilibrium multipolar Hamiltonian whose phase diagram contains robust antiferro-octupolar, ferro-octupolar, and partially polarized ferro-quadrupolar phases, alongside a putative Ising-octupolar regime and a strongly frustrated, liquid-like multipolar regime whose finite-size numerical signatures are compatible with Kitaev-type behavior. We further show that the induced multipolar order couples to the lattice, generating reversible trigonal and orthorhombic or tetragonal distortions that provide symmetry-resolved structural fingerprints in pump-probe experiments. In this way, our work establishes a general mechanism for the optical generation, control, and detection of hidden multipolar quantum states.