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Quantum spin circulator in Y junctions of Heisenberg chains
We show that a quantum spin circulator, a nonreciprocal device that routes
spin currents without any charge transport, can be achieved in Y junctions of
identical spin- Heisenberg chains coupled by a chiral three-spin
interaction. Using bosonization, boundary conformal field theory, and
density-matrix renormalization group simulations, we find that a chiral fixed
point with maximally asymmetric spin conductance arises at a critical point
separating a regime of disconnected chains from a spin-only version of the
three-channel Kondo effect. We argue that networks of spin-chain Y junctions
provide a controllable approach to construct long-sought chiral spin liquid
phases.Comment: 9 pages, 3 figure
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