Sandvik, A. (2017). Nearly fractionalized excitations in 2D quantum antiferromagnets. Perimeter Institute for Theoretical Physics. http://pirsa.org/17050086

MLA

Sandvik, Anders. Nearly fractionalized excitations in 2D quantum antiferromagnets. Perimeter Institute for Theoretical Physics, May. 25, 2017, http://pirsa.org/17050086

BibTex

@misc{ scitalks_17050086,
doi = {},
url = {http://pirsa.org/17050086},
author = {Sandvik, Anders},
keywords = {Quantum Matter},
language = {en},
title = {Nearly fractionalized excitations in 2D quantum antiferromagnets},
publisher = {Perimeter Institute for Theoretical Physics},
year = {2017},
month = {may},
note = {Talk #17050086 see, \url{https://scitalks.ca}}
}

The 2D S = 1/2 square-lattice Heisenberg model is a keystone of theoretical studies of quantum magnetism. It also has very good realizations in several classes of layered insulators with localized electronic spins. While spin-wave theory provides a good understanding of the antiferromagnetic ground state and low-lying excitations of the Heisenberg model, an anomaly in the excitations at higher energy around wave-number q = (\pi, 0) has been diffi_cult to explain. At first sight, the anomaly is just a suppression of the excitation energy by a few percent, but it also represents a more dramatic shift of spectral weight in the dynamic spin structure factor from the single- magnon (spin wave) pole to a continuum. Recent neutron scattering experiments on the quasi-2D material Cu(DCOO)2_.4D2O (the best realization so far of the 2D Heisenberg model) were even interpreted as a complete lack of magnon pole at the anomaly; instead it was suggested that the excitations there are fractional (spinons) [1]. I will discuss recent quantum Monte Carlo and stochastic analytic continuation results pointing to the existence of fragile q~(\pi,0) magnon excitations in the Heisenberg model [2], which can be fractionalized by interactions competing with the nearest-neighbor exchange coupling. This phenomenon can be understood phenomenologically within a simple theory of magnon-spinon mixing.