Van Hove singularity in the magnon spectrum of the antiferromagnetic quantum honeycomb lattice
Gabriele Sala, M. B. Stone, Binod K. Rai, Andrew F. May, Pontus Laurell, V. Ovidiu Garlea, Nicholas P. Butch, M. D. Lumsden, G. Ehlers, Ganesh Pokharel, A. Podlesnyak, David Mandrus, David Parker, Satoshi Okamoto, Gábor B. Halász, A. D. Christianson
Abstract
Abstract In quantum magnets, magnetic moments fluctuate heavily and are strongly entangled with each other, a fundamental distinction from classical magnetism. Here, with inelastic neutron scattering measurements, we probe the spin correlations of the honeycomb lattice quantum magnet YbCl 3 . A linear spin wave theory with a single Heisenberg interaction on the honeycomb lattice, including both transverse and longitudinal channels of the neutron response, reproduces all of the key features in the spectrum. In particular, we identify a Van Hove singularity, a clearly observable sharp feature within a continuum response. The demonstration of such a Van Hove singularity in a two-magnon continuum is important as a confirmation of broadly held notions of continua in quantum magnetism and additionally because analogous features in two-spinon continua could be used to distinguish quantum spin liquids from merely disordered systems. These results establish YbCl 3 as a benchmark material for quantum magnetism on the honeycomb lattice.