paper

Direct evidence for a gapless spin liquid by frustrating Néel antiferromagnetism

arXiv:1304.2630 · doi:10.1103/PhysRevB.88.060402

Abstract

By direct calculations of the spin gap in the frustrated Heisenberg model on the square lattice, with nearest- () and next-nearest-neighbor () super-exchange couplings, we provide a solid evidence that the spin-liquid phase in the frustrated regime is gapless. Our numerical method is based on a variational wave function that is {\it systematically} improved by the application of few Lanczos steps and allows us to obtain reliable extrapolations in the thermodynamic limit. The peculiar nature of the non-magnetic state is unveiled by the existence of S=1 gapless excitations at and . The magnetic transition can be described and interpreted by a variational state that is built from Abrikosov fermions having a gauge structure and four Dirac points in the spinon spectrum.

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