Zero Temperature Phase Diagram of the Classical Kane-Mele-Heisenberg Model

TL;DR

This paper maps the classical phase diagram of the Kane-Mele-Heisenberg model, identifying six phases, including both ordered and degenerate incommensurate states, and explores quantum fluctuation effects that select specific states.

Contribution

It provides a comprehensive classical phase diagram of the Kane-Mele-Heisenberg model using multiple methods and investigates quantum order-by-disorder effects on degenerate phases.

Findings

Six distinct classical phases identified.

Quantum fluctuations select specific states in phase III.

Degenerate incommensurate phases may also be influenced by quantum effects.

Abstract

The classical phase diagram of the Kane-Mele-Heisenberg model is obtained by three complementary methods: Luttinger-Tisza, variational minimization, and the iterative minimization method. Six distinct phases were obtained in the space of the couplings. Three phases are commensurate with long-range ordering, planar N{\'e}el states in horizontal plane (phase.I), planar states in the plane vertical to the horizontal plane (phase.VI) and collinear states normal to the horizontal plane (phase.II). However the other three, are infinitely degenerate due to the frustrating competition between the couplings, and characterized by a manifold of incommensurate wave-vectors. These phases are, planar helical states in horizontal plane (phase.III), planar helical states in a vertical plane (phase.IV) and non-coplanar states (phase.V). Employing the linear spin-wave analysis, it is found that the quantum fluctuations select a set of symmetrically equivalent states in phase.III, through the quantum order-by-disorder mechanism. Based on some heuristic arguments is argued that the same scenario may also occur in the other two frustrated phases VI and V.