Signatures of nonlinear magnetoelectricity in second harmonic spectra of SU(2) symmetry broken quantum many-body systems

TL;DR

This paper investigates how SU(2) symmetry breaking influences second harmonic spectra in quantum many-body systems, revealing signatures of nonlinear magnetoelectric effects through computational analysis of Hubbard models with spin-orbit and spin-phonon couplings.

Contribution

It introduces a perturbative framework for second order dynamical magnetoelectric susceptibilities in systems with broken SU(2) symmetry and demonstrates their signatures in spectra via computational methods.

Findings

Signatures of nonlinear ME effects appear in second harmonic spectra.

Peak intensities are maximized when Hubbard and SOC terms are comparable.

Both spin and charge contributions are observed in the spectra.

Abstract

Quantum mechanical perturbative expressions for second order dynamical magnetoelectric (ME) susceptibilities have been derived and calculated for a small molecular system using the Hubbard Hamiltonian with SU(2) symmetry breaking in the form of spin-orbit coupling (SOC) or spin-phonon coupling. These susceptibilities will have signatures in second harmonic generation spectra. We show that SU(2) symmetry breaking is the key to generate these susceptibilities. We have calculated these ME coefficients by solving the Hamiltonian for low lying excited states using Lanczos method. Varying the Hubbard term along with SOC strength, we find spin and charge and both spin-charge dominated spectra of dynamical ME coefficients. We have shown that intensities of the peaks in the spectra are highest when the magnitudes of Hubbard term and SOC coupling term are in similar range.