Quantum dynamics in a spin-1/2 square lattice $J_{1}$-$J_{2}$-$\delta$ altermagnet

TL;DR

This study explores the quantum dynamics of a frustrated spin-1/2 $J_1$-$J_2$-$elta$ Heisenberg model on a square lattice, revealing an altermagnetic ground state with split magnon spectra and complex excitations.

Contribution

It introduces the first detailed analysis of magnon and longitudinal excitations in an altermagnetic quantum spin model using tensor network and spin-wave methods.

Findings

Altermagnetic ground state identified for small $J_2$ and finite $elta$

Magnon spectrum exhibits splitting with maximum at rac{}{2}, rac{}{2} points

Low-energy longitudinal spectral weight also shows splitting, indicating complex quantum dynamics.

Abstract

A key feature of the newly discovered altermagnet is that its spin degeneracy is lifted, although it has an antiferromagnetic order and zero net magnetization. In this work, we investigate a frustrated spin-1/2 $J_1$-$J_2$-$\delta$ Heisenberg model on the square lattice by the tensor network methodin combination with the linear spin-wave theory, with our focus on both the magnon excitations and longitudinal excitations.For a small $J_2$ and a finite range of $\delta$ we demonstrate that such a model hosts an altermagnetic ground state. Its magnon spectrum is split into two branches and the largest splitting occurs at $\left(\pm\pi/2, \pm\pi/2\right)$ in the Brillouin zone. The magnitudes of splitting in the two magnon modes are equal with respect to the case of $\delta=0$. Dynamical spin structure factors show that the low-energy peak in the longitudinal spectral weight around $(\pi/2, \pi/2)$ is also split, and thus the relative positions of the magnon modes and longitudinal modes in energy may change in the presence of a finite $\delta$. These findings demonstrate that the altermagnets harbor more complex quantum dynamics than the conventional collinear antiferromagnets.