Tetragonal distortion yielding a two-singlet spin liquid in pyrochlore Tb2Ti2O7

The pyrochlore compound Tb2Ti2O7 is known to remain in a spin-liquid state down to the lowest attainable temperature (0.05 K), whereas current theories predict it should order into an antiferromagnetic structure. A number of models have been developed in order to resolve this discrepancy, but none of them could obtain a spin-liquid ground state. We present here a tentative explanation for the lack of magnetic order in Tb2Ti2O7 based on the presence of a Jahn-Teller-like distortion from the local trigonal symmetry and on the physics of the two-singlet system coupled by exchange.