Tracking local magnetic dynamics via high-energy charge excitations in a relativistic Mott insulator

TL;DR

This study uses advanced optical spectroscopy to explore how high-energy charge excitations can reveal and potentially control magnetic dynamics in a relativistic Mott insulator with complex magnetic phases.

Contribution

It demonstrates a novel method to map magnetic dynamics onto high-energy charge excitations in a strongly spin-orbit coupled Mott insulator.

Findings

Charge excitations delocalize via quasi-molecular orbitals

Magnetic dynamics occur at THz frequencies

High-energy charge excitations reflect magnetic interactions

Abstract

We use time- and energy-resolved optical spectroscopy to investigate the coupling of electron-hole excitations to the magnetic environment in the relativistic Mott insulator Na$_2$IrO$_3$. We show that, on the picosecond timescale, the photoinjected electron-hole pairs delocalize on the hexagons of the Ir lattice via the formation of quasi-molecular orbital (QMO) excitations and the exchange of energy with the short-range-ordered zig-zag magnetic background. The possibility of mapping the magnetic dynamics, which is characterized by typical frequencies in the THz range, onto high-energy (1-2 eV) charge excitations provides a new platform to investigate, and possibly control, the dynamics of magnetic interactions in correlated materials with strong spin-orbit coupling, even in the presence of complex magnetic phases.