The Ce3+ pseudospin - 1/2 degrees of freedom in the pyrochlore magnet Ce2Zr2O7 are known to possess dipole-octupole (DO) character, making it a candidate for novel quantum spin liquid (QSL) ground states at low temperatures. Earlier neutron scattering measurements, by ourselves [1] and others [2], saw dynamic correlations resembling spin ice, similar to that displayed by the well-studied Ho2Ti2O7 [3]. We report new heat capacity (Cp) measurements [4] on Ce2Zr2O7 which rise sharply at low temperatures, initially plateauing near 0.08 K, before falling off beyond 3 K. Above 0.5 K, the Cp data set can be fit to the results of a numerical linked cluster calculation, that allows robust estimates for the terms in the XYZ Hamiltonian expected for such DO pyrochlore systems. These results are shown to be consistent with new polarized neutron di ffraction results. We conclude that Ce2Zr2O7 realizes a U(1) -pi QSL state at low temperatures, and one that resides near the boundary between dipolar and octupolar character.

[1] J. Gaudet et al, Phys. Rev. Lett. 122, 187201 (2019).

[2] B. Gao et al., Nat. Phys. 15, 1052 (2019).

[3] S. T. Bramwell and M. J. P. Gingras, Science 294, 1495 (2001).

[4] E.M. Smith et al, arXiv:2108.01217.