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arXiv · 1710.00993

Nonlinear Phononic Control and Emergent Magnetism in Mott Insulating Titanates

Mingqiang Gu·James M. Rondinelli
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Abstract

Optical control of structure-driven magnetic order offers a platform for magneto-optical terahertz devices. We control the magnetic phases of $d^1$ 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 TiO$_6$ octahedral rotations that couple to static Ti--O Jahn-Teller distortions, through infrared-active phonon modes of LaTiO$_3$ and YTiO$_3$. 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.

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Mingqiang Gu, James M. Rondinelli. 2017-12-07. Nonlinear Phononic Control and Emergent Magnetism in Mott Insulating Titanates. https://doi.org/10.1103/physrevb.98.024102

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