Abstract
Quantum spin liquids (QSLs) have been at the forefront of correlated electron research ever since their proposal in 1973, and the realization that they belong to the broader class of intrinsic topological orders. According to received wisdom, QSLs can arise in frustrated magnets with low spin S, where strong quantum fluctuations act to destabilize conventional, magnetically ordered states. Here, we present a Z2 QSL ground state that appears already in the semiclassical, large-S limit. This state has both topological and symmetry-related ground-state degeneracy, and two types of gaps, a “magnetic flux” gap that scales linearly with S and an “electric charge” gap that drops exponentially in S. The magnet is the spin-S version of the spin-1/2 Kitaev honeycomb model, which has been the subject of intense studies in correlated electron systems with strong spin–orbit coupling, and in optical lattice realizations with ultracold atoms.
Highlights
Quantum spin liquids (QSLs) have been at the forefront of correlated electron research ever since their proposal in 1973, and the realization that they belong to the broader class of intrinsic topological orders
Notable examples are the resonating valence bond (RVB) state[1, 5, 12,13,14], the gapped QSL of the Toric code[6], and the gapless QSL phase of the spin-1/2 Kitaev honeycomb model[7]. Such massive superpositions arise in frustrated magnets with low spin S, which ideally have an infinite number of competing states and a strong tunneling between them[15]
The “magnetic flux” term of the Toric code arises from the zero-point energy of spin waves above the classical ground states, while the “electric charge” term stems from the tunneling between different classical states
Summary
Quantum spin liquids (QSLs) have been at the forefront of correlated electron research ever since their proposal in 1973, and the realization that they belong to the broader class of intrinsic topological orders. Notable examples are the resonating valence bond (RVB) state[1, 5, 12,13,14], the gapped QSL of the Toric code[6], and the gapless QSL phase of the spin-1/2 Kitaev honeycomb model[7] Such massive superpositions arise in frustrated magnets with low spin S, which ideally have an infinite number of competing states and a strong tunneling between them[15]. The ensuing Z2 QSL lives on top of a honeycomb superlattice of “frozen” spin dimers[16], which take only two possible configurations, instead of (2S + 1)[2] These two states are the pseudospin-1/2 degrees of freedom of the Toric code.
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