Abstract
We establish the appearance of a qualitatively new type of spin liquid with emergent exceptional points when coupling to the environment. We consider an open system of the Kitaev honeycomb model generically coupled to an external environment. In extended parameter regimes, the Dirac points of the emergent Majorana fermions from the original model are split into exceptional points with Fermi arcs connecting them. In glaring contrast to the original gapless phase of the honeycomb model that requires time-reversal symmetry, this new phase is stable against all perturbations. The system also displays a large sensitivity to boundary conditions resulting from the non-Hermitian skin effect with telltale experimental consequences. Our results point to the emergence of new classes of spin liquids in open systems that might be generically realized due to unavoidable couplings with the environment.
Highlights
Quantum spin liquids are low-temperature phases of matter with fractionalized excitations and emergent gauge fields [1,2,3,4,5]
We show that coupling a spin liquid to an environment can lead to a qualitatively new kind of phase that cannot occur in any closed system
In this Letter, we show that these phenomena can be realized in an interacting spin model, giving rise to a qualitatively new kind of spin liquid
Summary
We establish the appearance of a qualitatively new type of spin liquid with emergent exceptional points when coupling to the environment. Our results point to the emergence of new classes of spin liquids in open systems that might be generically realized due to unavoidable couplings with the environment. Band crossings with such exceptional points result in an unconventional square-root dispersion at low energies as opposed to a typical Dirac dispersion as seen in graphene These band crossings in two-dimensional (2D) systems are generic, unlike the accidental symmetry-protected crossings in graphene [19,22]. In this Letter, we show that these phenomena can be realized in an interacting spin model, giving rise to a qualitatively new kind of spin liquid We illustrate this by coupling the Kitaev honeycomb model [7] to an environment (Fig. 1, left panel). The two Dirac points generically split into four exceptional points
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