Quantum spin fluctuations in the spin-liquid state of Tb ₂Ti ₂O ₇

Neutron scattering experiments on a polycrystalline sample of the frustrated pyrochlore magnet Tb ₂Ti ₂O ₇, which does not show any magnetic order down to 50mK, have revealed that it shows condensation behavior below 0.4K from a thermally fluctuating paramagnetic state to a spin-liquid ground state with quantum spin fluctuations. Energy spectra change from quasielastic scattering to a continuum with a double-peak structure at energies of 0 and 0.8K in the spin-liquid state. Specific heat shows an anomaly at the crossover temperature.