Lack of Evidence for a Singlet Crystal Field Ground State in the Tb2Ti2O7 Magnetic Pyrochlore

摘要

We present new high resolution inelastic neutron scattering data on thecandidate spin liquid Tb2Ti2O7. We find that there is no evidence for a zerofield splitting of the ground state doublet within the 0.2 K resolution of theinstrument. This result contrasts with a pair of recent works on Tb2Ti2O7claiming that the spin liquid behavior can be attributed to a 2 K splitsinglet-singlet single-ion spectrum at low energies. We also reconsider theentropy argument presented in Chapuis {\it et al.} as further evidence of asinglet-singlet crystal field spectrum. We arrive at the conclusion thatestimates of the low temperature residual entropy drawn from heat capacitymeasurements are a poor guide to the single ion spectrum without understandingthe nature of the correlations.