Optical control of structure-driven magnetic order offers a platform for magneto-optical terahertz devices. We control the magnetic phases of d1 Mott insulating titanates using nonlinear phononics to transiently perturb the atomic structure based on density functional theory (DFT) simulations and solutions to a lattice Hamiltonian including nonlinear multi-mode interactions. We show that magnetism is tuned by indirect excitation of a Raman-active phonon mode, which affects the amplitude of the TiO6 octahedral rotations that couple to static Ti--O Jahn-Teller distortions, through infrared-active phonon modes of LaTiO3 and YTiO3. The mode excitation reduces the rotational angle, driving a magnetic phase transition from ferromagnetic (FM) to A-type antiferromagnetic (AFM), and finally a G-type AFM state. This novel A-AFM state arises from a change in the exchange interactions and is absent in the bulk equilibrium phase diagram, but it emerges as a dynamically accessible optically induced state under multi-mode excitations. Our work shows nonlinear phononic coupling is able to stabilize phases inaccessible to static chemical pressure or epitaxial strain.
@article{arxiv.1710.00993,
title = {Nonlinear Phononic Control and Emergent Magnetism in Mott Insulating Titanates},
author = {Mingqiang Gu and James M. Rondinelli},
journal= {arXiv preprint arXiv:1710.00993},
year = {2018}
}