## "Nearly deconfined spinon excitations in the square-lattice spin-1/2 Heisenberg antiferromagnet"

**Speaker:**Hui Shao, Beijing Computational Science Research Center

**When:**October 25, 2017 (Wed), 11:00AM to 12:30PM (add to my calendar)

**Location:**SCI 328

**Hosted by:**Anders Sandvik

*This event is part of the Condensed Matter Theory Seminar Series. *

We study the spin excitation spectrum of the spin-1/2 square-lattice Heisenberg antiferromagnet with QMC and an improved stochastic analytic continuation method. The spectra are in excellent agreement with recent neutron scattering experiments on Cu(DCOO)2·4D2O, where a broad spectral-weight continuum at wavevector q = (\pi,0) was interpreted as deconfined spinons. Our results show a similar reduction of the magnon weight and a large continuum. Upon turning on the Q interaction in the J-Q model, we observe a rapid reduction of the magnon weight to zero, well before the system undergoes a deconfined quantum phase transition into a non-magnetic spontaneously dimerized state. Based on these results, we re-interpret the picture of deconfined spinons at (\pi,0) in the experiments as nearly deconfined spinons—a precursor to deconfined quantum criticality. We also introduce an effective model of the excitations (one magnon or two spinons) which can reproduce the reduction of magnon weight and lowered excitation energy at (\pi,0) in the Heisenberg model, as well as the rapid loss of the (\pi,0) magnon with increasing Q in the J-Q model.