Two-dimensional quantum-spin-1/2 XXZ magnet in zero magnetic field: global thermodynamics from renormalization group theory

TL;DR

This paper uses renormalization group theory to comprehensively analyze the thermodynamics, phase transitions, and quantum properties of the two-dimensional XXZ spin-1/2 model across all temperatures and anisotropies.

Contribution

It provides a global thermodynamic analysis of the 2D XXZ model using numerical renormalization group, covering all anisotropies and temperature ranges for the first time.

Findings

Existence of long-range order at low temperatures.

Gapped excitations in the Ising-like regime.

Identification of quantum phase transitions at zero temperature.

Abstract

Phase diagram, critical properties and thermodynamic functions of the two-dimensional field-free quantum-spin-1/2 XXZ model has been calculated globally using a numerical renormalization group theory. The nearest-neighbor spin-spin correlations and entanglement properties, as well as internal energy and specific heat are calculated globally at all temperatures for the whole range of exchange interaction anisotropy, from XY limit to Ising limits, for both antiferromagnetic and ferromagnetic cases. We show that there exists long-range (quasi-long-range) order at low-temperatures, and the low-lying excitations are gapped (gapless) in the Ising-like easy-axis (XY-like easy-plane) regime. Besides, we identify quantum phase transitions at zero-temperature.