Magnetic Excitations in Spin-Orbit Coupled $d^4$ Mott Insulator on Square Lattice

TL;DR

This paper investigates magnetic order and excitations in spin-orbit coupled d^4 Mott insulators on a square lattice, considering crystal field effects and their impact on magnetic phases and spectra, with relevance to Ca2RuO4.

Contribution

It extends previous models by including tetragonal crystal field splitting to analyze its influence on magnetic phases and magnon spectra in d^4 Mott insulators.

Findings

Identified two magnetic phases with different moment orientations based on crystal field strength.

Calculated magnetic excitation spectra for both paramagnetic and ordered phases.

Discussed implications for the material Ca2RuO4.

Abstract

We study the magnetic order and excitations in strong spin-orbit coupled, Van Vleck-type, $d^4$ Mott insulators on a square lattice. Extending the previous work, we include the tetragonal crystal field splitting and explore its effects on magnetic phase diagram and magnon spectra. Two different ordered phases, with in-plane and out-of-plane orientation of the staggered moments, are found for the higher and lower values of the crystal field splitting, respectively. The magnetic excitation spectra for paramagnetic and magnetically ordered phases are calculated and discussed in the context of a candidate spin-orbit $d^4$ Mott insulator Ca$_2$RuO$_4$.