Spinon Confinement and the Quantum Criticality in the Weakly Coupled Spin-ladder Compound CaCu₂O₃

Abstract

Confinement describes how constituent particles are bound together by a confining interaction to form a resultant particle (e.g. confinement of 3 quarks to form a hadron). In condensed matter, confinement occurs in spin-ladders (two spin-1/2 Heisenberg, antiferromagnetic chains coupled together). Excitations of individual chains  are spinons but an infinitesimal inter-chain coupling confines them. All current ladders have large inter-chain interactions and are in the strong confinement limit with magnon excitations and are thus unable to reveal the confinement process. Here we present neutron scattering experiments on a weakly-coupled spin-ladder, which displays all the theoretically predictions of confinement including the bound-spinon singlet mode which is absent at strong coupling. This system is at the long sought after Wess-Zumino-Novikov-Witten quantum critical point which is predicted to also govern the n=5/2 Fractional Quantum Hall effect, and the S=1 chain with biquadratic exchange.

Speaker

Christian Rueggs