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arXiv · 2605.08049

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

Saikat Banerjee·Tara Steinhöfel·Florian Lange·Matthias Eschrig·Holger Fehske
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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 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 are the key result of this work: the first provides a direct optical handle on hidden octupolar order, while the second reorganizes the multipolar exchange landscape and opens an enlarged Kitaev-like multipolar liquid regime. Their interplay produces a nonequilibrium multipolar phase space inaccessible in equilibrium, enabling optical tuning among antiferro-octupolar, ferro-octupolar, partially polarized ferro-quadrupolar, Ising octupolar, and multipolar liquid phases. We further show that the induced multipolar order couples to the lattice, generating reversible trigonal and tetragonal distortions that provide structural fingerprints in pump-probe experiments. Our work establishes a general mechanism for the optical generation, control, and detection of hidden multipolar quantum states.

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Saikat Banerjee, Tara Steinhöfel, Florian Lange, Matthias Eschrig, Holger Fehske. 2026-05-08. Light-driven octupolar inverse Faraday effect and multipolar order in Mott insulators. https://arxiv.org/abs/2605.08049

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