Ising versus Potts criticality in a low-temperature magnetothermodynamics of a frustrated spin-1/2 Heisenberg triangular bilayer

TL;DR

This paper investigates the low-temperature magnetothermodynamics of a frustrated spin-1/2 Heisenberg triangular bilayer, revealing Ising and Potts criticality in its phase transitions through theoretical mapping and simulations.

Contribution

It demonstrates a mapping of the Heisenberg bilayer to an effective Ising model, uncovering Ising and Potts universality classes in its phase transitions, and compares these with exact diagonalization results.

Findings

Ferromagnetic interdimer coupling causes a zero-temperature magnetization jump.

Antiferromagnetic interdimer coupling leads to multistep magnetization with plateaus.

Transitions change from discontinuous to continuous with temperature, belonging to Ising and Potts universality classes.

Abstract

Low-temperature magnetization curves and thermodynamics of a frustrated spin-1/2 Heisenberg triangular bilayer with the antiferromagnetic intradimer interaction and either ferromagnetic or antiferromagnetic interdimer interaction are investigated in a highly frustrated parameter region, where localized many-magnon eigenstates provide the most dominant contribution to magnetothermodynamics. Low-energy states of the highly frustrated spin-1/2 Heisenberg triangular bilayer can be accordingly found from a mapping correspondence with an effective triangular-lattice spin-1/2 Ising model in a field. A description based on the effective Ising model implies that the frustrated Heisenberg triangular bilayer with the ferromagnetic interdimer coupling displays in a zero-temperature magnetization curve discontinuous magnetization jump, which is reduced upon increasing of temperature until a continuous field-driven phase transition from the Ising universality class is reached at a certain critical temperature. The frustrated Heisenberg triangular bilayer with the antiferromagnetic interdimer coupling contrarily exhibits multistep magnetization curve with intermediate plateaus at one-third and two-thirds of the saturation magnetization, whereas discontinuous magnetization jumps observable at zero temperature change to continuous field-driven phase transitions from the universality class of three-state Potts model at sufficiently low temperatures. Exact results and Monte Carlo simulations of the effective Ising model are confronted with full exact diagonalization data for the Heisenberg triangular bilayer in order to corroborate these findings.