Exact plaquette singlet phases in an orthogonal-plaquette model

TL;DR

This paper introduces a quantum spin-1/2 model with exact plaquette singlet ground states, phase transitions, and extensive degeneracy, providing insights into solvable models with potential realizations in quantum materials.

Contribution

The paper presents a new orthogonal-plaquette model with exactly solvable ground states and a detailed phase diagram analysis based on conserved quantities.

Findings

Two exact plaquette singlet ground states identified

An exact phase transition with extensive degeneracy occurs

Model based solely on Heisenberg interactions, feasible for quantum materials

Abstract

We introduce a quantum spin-1/2 model hosting two exact plaquette singlet ground states in extended parameter regimes. There is an exact phase transition between both phases, at which the system has an extensive ground-state degeneracy. Further, the model exhibits an extensive number of conserved quantities, which allow the prediction of additional phases. We exploit this feature and explore the phase diagram in detail for two specific parameter regimes. The model is based solely on Heisenberg interactions and seems sufficiently simple to be realized in quantum materials. A general scheme to determine exact singlet product states is briefly discussed.