Abstract

Light-induced breaking of time-reversal symmetry in insulating crystals is commonly attributed to the inverse Faraday effect, a weak magnetization generated by circularly polarized light. However, recent pump-probe experiments in SrTiO3 reported probe-polarization rotations associated with much larger fields [1], reportedly generated by coherent rotation of the ions [2]. Here we propose an alternative mechanism to explain experimental results: a light-induced Faraday effect arising from the antisymmetric component of the nonlinear optical susceptibility [3]. We show that this contribution appears already at the electronic level due to the breaking of Kleinman symmetry at finite frequency, even far from resonances. Phonon resonance is also expected to enhance the response. This effect can be understood as a dynamical breaking of time-reversal symmetry, where circularly polarized light acts as an effective internal magnetic field to induce the probe rotation, with an estimated magnitude of 30 mT, consistent with experiments.

[1] M. Basini, M. Pancaldi, B. Wehinger, M. Udina, V. Unikandanunni, T. Tadano, M.C. Hoffmann, A.V. Balatsky, and S. Bonetti, Nature 628, 534 (2024) [2] D.M. Juraschek, M. Fechner, A.V. Balatsky, and N.A. Spaldin, Phys. Rev. Mat. 1, 014401 (2017) [3] N. Sellati, J. Fiore, and L. Benfatto, in preparation (2026)