Matthias Gohlke

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The characterization of quantum spin liquid (QSL) phases in Kitaev materials has been a subject of intensive studies over the recent years, both theoretically and experimentally. The Kitaev-Gamma model with bond-dependent diagonal and off-diagonal exchange has been considered as a minimal model in this context. Many theoretical studies have focused on spatially isotropic coupling strength along the different bonds in an attempt to simplify the problem. However, Kitaev materials often have a reduced lattice symmetry that allows for different coupling strength along the bonds, or the lattice symmetry can be reduced by external means.
Here, we consider a Kitaev-Gamma model with varying coupling strength along one of the bonds connecting the limit of isolated chains to the two-dimensional model. The chain limit is known to exhibit an emergent $SU(2)_1$ Tomonaga-Luttinger liquid (TLL) phase [Yang et al. (2020)]. In the isotropic limit the nature of the phase diagram is still under debate. Various phases---including magnetically ordered, incommensurate, quantum paramagnetic, as well as a quantum spin liquid---have been proposed depending on the applied method and/or underlying assumptions.
Using ED on a symmetric cluster and iMPS, we map out the phase diagram in between the two limits. Our numerical results suggest that the isotropic limit is close to a phase transition between a trivial paramagnet and a quantum paramagnetic phase with a strong one-dimensional character, that can be traced back to the TLL phase in the chain limit. This proximate TLL would be different from the adjacent KSL in that it exhibits spinon-like excitation similar in nature to the 1D Heisenberg AF.

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Okinawa Institute of Science and Technology
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Contact: Simon Trebst