Quasiparticles governing the zero-temperature dynamics of the 1D spin-1/2 Heisenberg antiferromagnet in a magnetic field

TL;DR

This paper uses Bethe ansatz to identify new quasiparticles called psinons and antipsinons that govern the zero-temperature dynamics of the 1D spin-1/2 Heisenberg antiferromagnet in a magnetic field, providing detailed spectral analysis.

Contribution

It introduces the concept of psinons and antipsinons as new quasiparticles and characterizes their role in the dynamical properties of the 1D Heisenberg antiferromagnet under magnetic field.

Findings

Identification of psinons and antipsinons as key quasiparticles.

Calculation of spectral boundaries and densities of states.

Prediction of lineshapes for dynamic structure factors.

Abstract

The T=0 dynamical properties of the one-dimensional (1D) $s=1/2$ Heisenberg antiferromagnet in a uniform magnetic field are studied via Bethe ansatz for cyclic chains of $N$ sites. The ground state at magnetization $0<M_z<N/2$, which can be interpreted as a state with $2M_z$ spinons or as a state of $M_z$ magnons, is reconfigured here as the vacuum for a different species of quasiparticles, the {\em psinons} and {\em antipsinons}. We investigate three kinds of quantum fluctuations, namely the spin fluctuations parallel and perpendicular to the direction of the applied magnetic field and the dimer fluctuations. The dynamically dominant excitation spectra are found to be sets of collective excitations composed of two quasiparticles excited from the psinon vacuum in different configurations. The Bethe ansatz provides a framework for (i) the characterization of the new quasiparticles in relation to the more familiar spinons and magnons, (ii) the calculation of spectral boundaries and densities of states for each continuum, (iii) the calculation of transition rates between the ground state and the dynamically dominant collective excitations, (iv) the prediction of lineshapes for dynamic structure factors relevant for experiments performed on a variety of quasi-1D antiferromagnetic compounds, including KCuF$_3$, Cu(C$_4$H$_4$N$_2)(NO_3)_2$, and CuGeO$_3$.