title: Schwinger-Keldysh semionic approach for quantum spin systems.
abstract: 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.
authors.affiliation: Institut für Theoretische Physik, Universität Würzburg, D-97074 Würzburg, Germany.
authors.forename: M N
authors.initials: MN
authors.lastname: Kiselev
authors.forename: R
authors.initials: R
authors.lastname: Oppermann