Energy spectrum and low temperature entropy of the spin-1/2 triangular antiferromagnet

MEZIO, ALEJANDRO; SPOSETTI, CINTIA N.; MANUEL, LUIS O.; TRUMPER, ADOLFO E.

San Carlos de Bariloche

Conferencia; 16th International Conference on Recent Progress in Many-Body Theories; 2011

Centro Atómico Bariloche - Comisión Nacional de Energía Atómica

We present results of the dynamical structure factor for the spin 1/2 triangular Heisenberg model, recently computed by us, using the mean field Schwinger boson theory. We find that a reconstructed dispersion, resulting from a non trivial redistribution of the spectral weight, agrees quite well with the spin excitation spectrum found with series expansions. In particular, we recover the strong renormalization with respect to linear spin wave theory along with the appearance of rotonlike minima at the midpoints of edges of the hexagonal Brillouin zone. By computing the densitydensity dynamical structure factor, we identify an unphysical weak signal of the spin excitation spectrum with the relaxation of the local constraint of the Schwinger bosons assumed at the mean field level. Finally, by selecting appropriately the physical spin excitations, we show that within the context of the present bosonic spinon theory, the high values of entropy found at low temperatures with series expansion can be explained due to the presence of the roton excitations.