Dresden 2020 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 43: Frustrated Magnets - Strong Spin-Orbit Coupling 2 (joint session TT/MA)

TT 43.9: Vortrag

Mittwoch, 18. März 2020, 17:15–17:30, HSZ 304

Nonlinear spin-wave theory for the Heisenberg-Kitaev model in a magnetic field — •Pedro M. Cônsoli1,2, Lukas Janssen2, Matthias Vojta2, and Eric C. Andrade11Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, Brazil — 2Institut für Theoretische Physik, TU Dresden, Dresden, Germany

The exact solution of Kitaev’s honeycomb model and the ensuing realization that it gives rise to chiral Majorana edge modes in a small and properly oriented magnetic field sparked an intense search for a physical mechanism capable of replicating such a system in real materials. This missing link was provided by Khaliullin and Jackeli, who showed that an interplay between crystal field effects and strong spin-orbit coupling originates the Kitaev interaction along with a Heisenberg exchange in a class of Mott insulators. Hence, the Heisenberg-Kitaev Hamiltonian became a minimal model to describe Kitaev materials and was subsequently studied in much detail. Still, several questions related to effects of external perturbations remain unanswered.

Here, we discuss the physics of the Heisenberg-Kitaev model in the presence of a magnetic field applied along two different directions: [100] and [111], for which an intricate classical phase diagram has been reported. In both settings, we employ spin-wave theory for a number of ordered phases to compute magnetization curves and phase boundaries in next-to-leading order in 1/S, with S being the spin size. In this way, we show that quantum corrections substantially modify the phase diagram. Finally, we compare our spin-wave theory results to exact diagonalization calculations performed on a 24-site cluster.

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