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تسجيل مستخدم جديدA simple anisotropic three-dimensional quantum spin liquid with fracton topological order
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We present a three-dimensional cubic lattice spin model, anisotropic in the $hat{z}$ direction, that exhibits fracton topological order. The latter is a novel type of topological order characterized by the presence of immobile pointlike excitations, named fractons, residing at the corners of an operator with two-dimensional support. As other recent fracton models, ours exhibits a subextensive ground state degeneracy: On an $L_xtimes L_ytimes L_z$ three-torus, it has a $2^{2L_z}$ topological degeneracy, and an additional non-topological degeneracy equal to $2^{L_xL_y-2}$. The fractons can be combined into composite excitations that move either in a straight line along the $hat{z}$ direction, or freely in the $xy$ plane at a given height $z$. While our model draws inspiration from the toric code, we demonstrate that it cannot be adiabatically connected to a layered toric code construction. Additionally, we investigate the effects of imposing open boundary conditions on our system. We find zero energy modes on the surfaces perpendicular to either the $hat{x}$ or $hat{y}$ directions, and their absence on the surfaces normal to $hat{z}$. This result can be explained using the properties of the two kinds of composite two-fracton mobile excitations.
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