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arXiv · 2007.03717

Heisenberg-Kitaev model in a magnetic field: $1/S$ expansion

Pedro M. Cônsoli·Lukas Janssen·Matthias Vojta·Eric C. Andrade
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Abstract

The exact solution of Kitaev's spin-$1/2$ honeycomb spin-liquid model has sparked an intense search for Mott insulators hosting bond-dependent Kitaev interactions, of which $\mathrm{Na}_{2}\mathrm{IrO}_{3}$ and $α-\mathrm{RuCl}_{3}$ are prime examples. Subsequently, it has been proposed that also spin-$1$ and spin-$3/2$ analogs of Kitaev interactions may occur in materials with strong spin-orbit coupling. As a minimal model to describe these Kitaev materials, we study the Heisenberg-Kitaev Hamiltonian in a consistent $1/S$ expansion, with $S$ being the spin size. We present a comprehensive study of this model in the presence of an external magnetic field applied along two different directions, [001] and [111], for which an intricate classical phase diagram has been reported. In both settings, we employ spin-wave theory in a number of ordered phases to compute phase boundaries at the next-to-leading order in $1/S$ and show that quantum corrections substantially modify the classical phase diagram. More broadly, our work presents a consistent route to investigate the leading quantum corrections in spin models that break spin-rotational symmetry.

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Pedro M. Cônsoli, Lukas Janssen, Matthias Vojta, Eric C. Andrade. 2020-11-03. Heisenberg-Kitaev model in a magnetic field: $1/S$ expansion. https://doi.org/10.1103/physrevb.102.155134

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