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

TL;DR

This study uses high-resolution neutron scattering to investigate the ground state of Tb2Ti2O7, finding no evidence for a singlet-doublet splitting and challenging previous interpretations of its spin liquid behavior.

Contribution

The paper provides new experimental data that refutes the existence of a low-energy singlet-singlet crystal field splitting in Tb2Ti2O7, questioning prior models based on entropy and heat capacity analyses.

Findings

No zero field splitting within 0.2 K resolution.

Contradicts previous claims of a 2 K singlet-singlet gap.

Highlights limitations of entropy estimates for crystal field spectra.

Abstract

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