Possible valence-bond condensation and quantum spin liquid phase in the S=1/2 antiferromagnet Y3Cu2Sb3O14

We have identified a new Cu based system, Y3Cu2Sb3O14 which appears to have a geometrically 3D network of S=1/2 Cu2+ ions. Our studies show that the magnetic susceptibility χ(T), specific heat Cp(T), electron spin resonance (ESR), 89Y nuclear magnetic resonance (NMR), and muon spin relaxation (µSR) confirm the absence of any long-range magnetic ordering and the persistence of spin dynamics down to 77 mK in spite of large Curie-Weiss (CW) temperature, θ_CW= -33 K. From ESR, µSR, and 89Y NMR we find evidence of a transition at about 65 K which we suggest arises from a 2/3rd of the spins condensing into a singlet state. Another transition is seen with an onset at about 10 K in µSR, and 89Y NMR signifying the condensation of the remaining 1/3rd spins into a spin liquid state. Through inelastic neutron scattering, we propose to explore the magnetic excitation spectrum (high energy and low energy) of powder samples of the Y3Cu2Sb3O14. More specifically, we are looking for the spin excitation continuum and the relative inelastic spectral weight from the low (T<60 K) and high-temperature (T>60 K) as was obtained for LiZn2Mo3O8.