Observation of extended scattering continua characteristic of spin fractionalization in the 2D frustrated quantum magnet Cs2CuCl4 by neutron scattering

TL;DR

This study uses neutron scattering to reveal extended excitation continua in Cs2CuCl4, indicating fractionalization of spin waves into spinons, characteristic of a resonating-valence-bond state in a 2D frustrated quantum magnet.

Contribution

It provides experimental evidence of spin fractionalization and distinguishes between magnon and spinon excitations in Cs2CuCl4, highlighting a crossover in excitation nature.

Findings

Observation of excitation continua above magnetic order transition

Sharp magnons at low energies in the ordered phase

Continuum well described by a two-spinon model

Abstract

The magnetic excitations of the quasi-2D spin-1/2 Heisenberg antiferromagnet on an anisotropic triangular lattice Cs2CuCl4 are explored throughout the 2D Brillouin zone using inelastic neutron scattering. In the spin liquid phase above the transition to magnetic order extended excitation continua are observed, characteristic of fractionalization of S=1 spin waves into pairs of deconfined S=1/2 spinons and the hallmark of a resonating-valence-bond (RVB) state. The weak inter-layer couplings stabilize incommensurate spiral order at low temperatures and in this phase sharp magnons carrying a small part of the total scattering weight are observed at low energies below the continuum lower boundary. Linear spin-wave theory including one- and two-magnon processes can describe the sharp magnon excitation, but not the dominant continuum scattering, which instead is well described by a parameterized two-spinon cross-section. Those results suggest a cross-over in the nature of excitations from S=1 spin waves at low energies to S=1/2 spinons at medium to high energies, which could be understood if Cs2CuCl4 was in the close proximity of a transition between a fractional spin liquid and a magnetically-ordered phase.