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Inelastic neutron scattering is used to study the low-energy magnetic excitations in the spin-1 triangular lattice of the 6H-B phase of Ba3NiSb2O9. We study two powder samples: Ba3NiSb2O9 synthesized under high pressure and Ba2.5Sr0.5NiSb2O9 in which chemical pressure stabilizes the 6H-B structure. The measured excitation spectra show broad gapless and nondispersive continua at characteristic wave vectors. Our data rules out most theoretical scenarios that have previously been proposed for this phase, and we find that it is well described by an exotic quantum spin liquid with three flavors of unpaired fermionic spinons, forming a large spinon Fermi surface. [ABSTRACT FROM AUTHOR]

We present an in-depth study of the magnetic properties of the spin-1 antiferromagnet 6HB-Ba3 NiSb2 O9. μSR measurements demonstrate that this material shows no static magnetism down to temperatures as low as 20 mK, making it a likely candidate for a quantum spin liquid state. Sb121 NMR shift measurements show that the local, intrinsic susceptibility levels off at temperatures below ~ 60 K. The NMR spin-lattice relaxation rate 1/T1 is essentially constant in temperature and the muon relaxation rate exhibits a low-temperature relaxation plateau, all indications of gapless spin excitations. Our local probe measurements are discussed in the context of several theories proposed for this material. [ABSTRACT FROM AUTHOR]