Distinct spinon and holon dispersions in photoemission spectral functions from one-dimensional SrCuO2

Spin and charge are inseparable traits of an electron, but in one-dimensional solids, theory predicts their separation into collective modes - as independent excitation quanta ( or particles) called spinons and holons. Experimentalists have long sought to verify this effect. Angle-resolved photoemission ( ARPES) should provide the most direct evidence of spin - charge separation, as the single quasiparticle peak splits into a spinon -holon two-peaklike structure. Despite extensive ARPES experiments, the unambiguous observation of the two-peak structure has remained elusive. Here we report ARPES data from SrCuO2, made possible by recent technological developments, that unequivocally show the spinon -holon two-peak structure and their distinct dispersions. The spinon and holon branches are found to have energy scales of similar to 0.43 and 1.3 eV, respectively, which are in quantitative agreement with the theoretical predictions.