Spinons and Damped Phonons in Spin-1/2 Quantum-Liquid Ba₄Ir₃O₁₀ Observed by Raman Scattering

In spin-1/2 Mott insulators, non-magnetic quantum spin liquid phases are often argued to arise when the system shows no magnetic ordering, but identifying positive signatures of these phases or related spinon quasiparticles can be elusive. Here we use Raman scattering to provide three signatures for spinons in a possible spin-orbit quantum liquid material Ba₄Ir₃O₁₀: (1) A broad hump, which we show can arise from Luttinger Liquid spinons in Raman with parallel photon polarizations normal to 1D chains;  (2) Strong phonon damping from phonon-spin coupling via the spin-orbit interaction; and (3) the absence of (1) and (2) in the Neel ordered phase of the same compound where 2% of Ba is substituted by Sr. The phonon damping via itinerant spinons in this quantum-liquid insulator suggests a new mechanism for enhancing thermoelectricity in strongly correlated conductors, through a neutral quantum liquid that does not affect electronic transport.