Ultrafast dynamics in relativistic Mott insulators

Abstract

We study the photoinduced ultrafast dynamics in relativistic Mott insulators, i.e., Mott insulators with strong spin-orbit coupling. For this purpose, we consider a minimal one-band Hubbard model on lattices with square and triangular symmetries, as relevant for layered transition metal compounds such as Sr2IrO4. Depending on the lattice and the spin-orbit coupling, the systems have canted antiferromagnetic or 120 • order. They are excited by simulating a short laser pulse, and the dynamics is solved using nonequilibrium dynamical mean-field theory. The pulse generates hot carriers, which subsequently perturb the magnetic order due to the coupling between the collective order and photocarriers. We find that this dynamics, which is known form regular antiferromagnets, depends sensitively on the spatial structure of the spin-orbit coupling. On the triangular lattice, in particular, relaxation times are influenced by the spin-orbit coupling for the chiral 120 • order, while on the square lattice with canted antiferromagnetic order the spin-orbit induced canting angle remains unchanged after the excitation. Our study opens up new possibilities of controlling magnetism and exotic spin states on the ultrafast timescales.

Nonequilibrium dynamics of α-RuCl3 – a time-resolved magneto-optical spectroscopy study

“…When these charge excitations hop through the lattice, they continuously perturb and destroy the magnetic order. 53 This can be interpreted as creating spin defects, which naturally quench the zigzag order locally and hence decrease the zigzag antiferromagnetic order parameter. The strong charge-spin coupling has been theoretically proposed to display an efficient nonthermal demagnetization process.…”

Nonequilibrium dynamics of $α$-RuCl$_{3}$ -- a time-resolved magneto-optical spectroscopy study

“…By this charge excitation multiple spinless quasiparticles are created, such that magnetic moments are effectively removed from the lattice. When these charge excitations hop through the lattice, they continuously perturb and destroy the magnetic order [53]. This can be interpreted as creating spin defects, which naturally quench the zigzag order locally and hence decrease the zigzag antiferromagnetic order parameter.…”

The application of broadband ultrafast spectroscopy to reveal structural, magnetic and electronic dynamics in quantum materials

“…For example, the model is blind to the mechanism of perturbation beyond imposing an instantaneous change, which is something that will depend on the dominant energy scale of the system. Indeed, while charge transfer in any Mott insulator is expected to produce rapid demagnetization [65], the exact nature of the spin-orbit coupling and the exchange interaction are likely key factors for explaining the magnitude and speed of the switching process [66]. Despite the limitations of the model, this approach allows us to explore the basic response of a system to a disruption of long-range order and highlights the role played by the degeneracy of the spin-disordered state in preventing a rapid recovery.…”