Spinon

Spinon is a quasiparticle excitation that carries spin 1/2 but no electric charge, arising in certain strongly interacting magnetic systems. It is an emergent, fractionalized degree of freedom that can appear when the collective spin dynamics cannot be described by conventional magnons. Spinons exemplify how many-body quantum effects can produce excitations with quantum numbers different from those of the elementary constituents.

In one-dimensional spin-1/2 Heisenberg antiferromagnets, the elementary excitations are spinons rather than magnons. Spinons carry spin-1/2 and exist as pairs to conserve total spin, forming a continuum of excitations in energy and momentum. This continuum, predicted by Bethe ansatz solutions, contrasts with the sharp spin-wave peaks seen in higher-dimensional magnets and provides a canonical setting for spinon physics.

In two dimensions and in quantum spin liquids, spinons can persist as deconfined excitations in the absence of magnetic order at zero temperature. Depending on the theoretical description, spinons may be fermionic or bosonic and can couple to emergent gauge fields. Some models feature a spinon Fermi surface or Dirac spinons, while others realize Z2 spin liquids with gapped excitations and topological order. The concept of spinons thus extends beyond simple chains to a broader class of frustrated magnets and exotic states of matter.

Experimental evidence for spinons comes from inelastic neutron scattering and related probes, which often reveal broad continua of magnetic scattering rather than sharp magnons. Notable materials discussed in this context include quasi-one-dimensional cuprates such as Sr2CuO3 and kagome-lattice compounds like Herbertsmithite, where signatures of fractionalized spin excitations have been reported.