Abstract
We will introduce a new variational method to compute the low-energy excitation spectrum of an extended Kitaev model on the Honeycomb lattice, which includes Heisenberg, Gamma and Zeeman terms. The method reveals the physical origin of the asymmetry in the stability range of Kitaev spin liquid phases around the ferromagnetic and antiferromagnetic Kitaev points. It also reveals the emergence of bound states of fractionalized excitations in the proximity of the quantum phase transition between the Kitaev spin liquid and different magnetically ordered states induced by the Heisenberg and terms that have been reported in multiple numerical works. These bound states, which appear below the continuum of matter Majorana fermion excitations, can be used as fingerprints of the quantum spin liquid phase.
Finally, we will see that the same method can be used to derive a low-energy theory of the continuous transition between different spin liquids induced by a magnetic field applied along the (111) direction. According to this theory, the field-induced spin liquid is gapped and belongs to Kitaev's 16-fold way. Specifically, the low-field non-Abelian liquid with Chern number transitions into an Abelian liquid. The critical field and the field-dependent behaviors of key physical quantities are in good quantitative agreement with published numerical results. Furthermore, we derive an effective field theory for the field-induced critical point which readily explains the ostensibly gapless nature of the intermediate-field spin liquid.
This event is organized by the HKU-UCAS Joint Institute of Theoretical and Computational Physics and HK Institute of Quantum Science & Technology