Phase diagram of the XXZ ferrimagnetic spin-(1/2, 1) chain in the presence of transverse magnetic field

TL;DR

This paper maps the phase diagram of a ferrimagnetic spin-(1/2, 1) chain under a transverse magnetic field, revealing phase transitions, magnetization plateaus, and symmetry breaking using numerical and analytical methods.

Contribution

It provides the first detailed phase diagram of the anisotropic ferrimagnetic chain with transverse field, combining DMRG and spin wave theory to analyze quantum phases and critical points.

Findings

Magnetization plateau exists only in the isotropic case with U(1) symmetry.

The system transitions from Nél to spin-flop to paramagnetic phases as field increases.

Quantum critical points depend on anisotropy and are characterized by symmetry breaking.

Abstract

We investigate the phase diagram of an anisotropic ferrimagnet spin-(1/2, 1) in the presence of a non-commuting (transverse) magnetic field. We find a magnetization plateau for the isotropic case while there is no plateau for the anisotropic ferrimagnet. The magnetization plateau can appear only when the Hamiltonian has the U(1) symmetry in the presence of the magnetic field. The anisotropic model is driven by the magnetic field from the N\'{e}el phase for low fields to the spin-flop phase for intermediate fields and then to the paramagnetic phase for high fields. We find the quantum critical points and their dependence on the anisotropy of the aforementioned field-induced quantum phase transitions. The spin-flop phase corresponds to the spontaneous breaking of Z2 symmetry. We use the numerical density matrix renormalization group and analytic spin wave theory to find the phase diagram of the model. The energy gap, sublattice magnetization, and total magnetization parallel and perpendicular to the magnetic field are also calculated. The elementary excitation spectrums of the model are obtained via the spin wave theory in the three different regimes depending on the strength of the magnetic field.