Spinons and triplons in spatially anisotropic frustrated antiferromagnets

TL;DR

This paper investigates elementary excitations in spatially anisotropic frustrated antiferromagnets, identifying spinons and triplons as key features, and validates the theory with experimental neutron scattering data.

Contribution

It introduces an effective Schrödinger equation approach for weak interchain coupling, revealing the presence of spinons and triplons in these materials, supported by experimental agreement.

Findings

Quantitative match with neutron scattering data

Identification of spinons and triplons as excitations

Triplons are a generic feature of such systems

Abstract

The search for elementary excitations with fractional quantum numbers is a central challenge in modern condensed matter physics. We explore the possibility in a realistic model for several materials, the spin-1/2 spatially anisotropic frustrated Heisenberg antiferromagnet in two dimensions. By restricting the Hilbert space to that expressed by exact eigenstates of the Heisenberg chain, we derive an effective Schr\"odinger equation valid in the weak interchain-coupling regime. The dynamical spin correlations from this approach agree quantitatively with inelastic neutron measurements on the triangular antiferromagnet Cs_2CuCl_4. The spectral features in such antiferromagnets can be attributed to two types of excitations: descendents of one-dimensional spinons of individual chains, and coherently propagating "triplon" bound states of spinon pairs. We argue that triplons are generic features of spatially anisotropic frustrated antiferromagnets, and arise because the bound spinon pair lowers its kinetic energy by propagating between chains.