Phys. Rev. Lett. 85, 5631–5634 (2000)Schwinger-Keldysh Semionic Approach for Quantum Spin SystemsReceived 14 July 2000; published in the issue dated 25 December 2000 We derive a path-integral Schwinger-Keldysh approach for quantum spin systems. This is achieved by means of a semionic representation of spins as fermions with imaginary chemical potential. The major simplifying feature in comparison with other representations (Holstein-Primakoff, Dyson-Maleev, slave bosons/fermions, etc.) is that the local constraint is taken into account exactly. As a result, the standard diagram technique with the usual Feynman codex is constructed. We illustrate the application of this technique for the Néel and spin-liquid states of the antiferromagnetic Heisenberg model. © 2000 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevLett.85.5631
DOI:
10.1103/PhysRevLett.85.5631
PACS:
75.10.-b, 75.40.Gb, 71.10.Fd
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