Abstract:
Spin excitations in a magnet with ordered moments are magnons,
quantized spin waves that behave like particles with integer spin and
Bose-Einstein statistics. A magnet lacking long-range order cannot
support spin waves and may have unusual magnetic excitations with
noninteger spin and different statistics. Heisenberg antiferromagnets
with spins of length S=1/2 on kagome and hyperkagome lattices have
emerged as a leading candidate for novel quantum physics. We show [1]
that magnetic excitations in this system are spinons, quasiparticles
with spin 1/2 and Fermi-Dirac statistics. The ground state of the
system is a quantum liquid or solid of small, heavy S=0 pairs of
spinons with a large density of nonmagnetic (Delta S=0) excitations at
low energies. A magnetic (Delta S=1) excitation amounts to breaking up
a pair into two spinons, a process with a threshold energy of 0.06
exchange constants.
[1] Z. Hao and O. Tchernyshyov, Phys. Rev. Lett. 103, 187203 (2009).