Selection rules for ultrafast laser excitation and detection of spin correlations dynamics in a cubic antiferromagnet

TL;DR

This paper derives selection rules for ultrafast laser excitation and detection of spin correlation dynamics in cubic antiferromagnets, providing a microscopic understanding of how to probe these correlations with high spatial and temporal resolution.

Contribution

It introduces a simple microscopic model that establishes polarization-based selection rules for exciting and detecting spin correlations, enhancing the ability to study magnetic dynamics at ultrashort scales.

Findings

Selection rules for pump and probe polarization to isolate spin correlation dynamics.

Spin correlations influence optical anisotropy even without spin-orbit coupling.

Dynamics of the antiferromagnetic order parameter are linked to small magnetic anisotropy.

Abstract

Exchange interactions determine the correlations between microscopic spins in magnetic materials. Probing the dynamics of these spin correlations on ultrashort length and time scales is, however rather challenging, since it requires simultaneously high spatial and high temporal resolution. Recent experimental demonstrations of laser-driven two-magnon modes - zone-edge excitations in antiferromagnets governed by exchange coupling - posed questions about the microscopic nature of the observed spin dynamics, the mechanism underlying its excitation, and their macroscopic manifestation enabling detection. Here, on the basis of a simple microscopic model, we derive the selection rules for cubic systems that describe the polarization of pump and probe pulses required to excite and detect dynamics of nearest-neighbor spin correlations, and can be employed to isolate such dynamics from other magnetic excitations and magneto-optical effects. We show that laser-driven spin correlations contribute to optical anisotropy of the antiferromagnet even in the absence of spin-orbit coupling. In addition, we highlight the role of subleading anisotropy in the spin system and demonstrate that the dynamics of the antiferromagnetic order parameter occurs only in next-to-leading order, determined by the smallness of the magnetic anisotropy as compared to the isotropic exchange interactions in the system. We expect that our results will stimulate and support further studies of magnetic correlations on the shortest length and time scale.