Spinon continuum in the Heisenberg quantum chain compound Sr2V3O9

Magnetic excitations in the spin chain candidate Sr2V3O9 have been investigated by inelastic neutron scattering on a single crystal sample. A spinon continuum with a bandwidth of similar to 22 meV is observed along the chain formed by alternating magnetic V4+ and nonmagnetic V5+ ions, which reveals the importance of the orbital degree of freedom in determining the chain axis as identified by prior electronic structure calculations. Incipient magnetic Bragg peaks due to weak ferromagnetic interchain couplings emerge when approaching the magnetic transition at TN similar to 5.3 K, while the excitations remain gapless within the instrumental resolution. Comparisons to the Bethe ansatz, density matrix renormalization group calculations, and effective field theories confirm Sr2V3O9 as a host of weakly coupled S = 1/2 chains dominated by antiferromagnetic intrachain interactions of similar to 7.1(1) meV.