Nonlinear Phononic Control and Emergent Magnetism in Mott Insulating Titanates

TL;DR

This paper demonstrates how nonlinear phononics can transiently control magnetic phases in Mott insulating titanates, enabling access to novel magnetic states not achievable through static means.

Contribution

It introduces a method to manipulate magnetic order via nonlinear phononic excitations, revealing dynamically accessible magnetic phases in titanates.

Findings

Magnetism is tuned by indirect excitation of Raman-active phonons.

A novel $A$-type antiferromagnetic state is induced dynamically.

Nonlinear phononic coupling stabilizes phases inaccessible by static methods.

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.