Research: Two-Peak Heat Capacity Accounts for 𝑅⁢ln⁡(2) Entropy and Ground State Access in the Dipole-Octupole Pyrochlore Ce2⁢Hf2⁢O7

This study explores the dipole-octupole pyrochlore Ce₂Hf₂O₇, a promising candidate for realizing a quantum spin liquid. It represents a significant technical advance, achieving heat capacity measurements on a high-quality single crystal down to 0.02 K (panel a). These measurements reveal two clear features: a broad Schottky-like peak near 0.065 K, also observed in sister compounds, and a sharper peak at ~0.025 K. Integrating the measured specific heat accounts for the full Rln(2) entropy of the Ce³⁺ pseudospin-½ doublet, implying that the low-temperature peak marks access for the ground state regime of the compound. Inelastic neutron scattering on both powder and single-crystal samples, combined with theoretical modeling using numerical linked-cluster expansions and quantum Monte Carlo, is consistent with the existence of a π-flux QSL phase (parameter A in panel b). The results for the first time demonstrate experimental access to the ground-state regime of the dipole-octupole pyrochlore family, paving the way for future experiments to clarify the true nature of this ground state.

E. M. Smith, A. Fitterman, R. Schäfer, B. Placke, A. Woods, S. Lee, S. H.-Y. Huang, J. Beare, S. Sharma, D. Chatterjee, C. Balz, M. B. Stone, A. I. Kolesnikov, A. R. Wildes, E. Kermarrec, G. M. Luke, O. Benton, R. Moessner, R. Movshovich, A. D. Bianchi, B. D. Gaulin,
Two-Peak Heat Capacity Accounts for 𝑅⁢ln⁡(2) Entropy and Ground State Access in the Dipole-Octupole Pyrochlore Ce₂⁢Hf₂⁢O₇,
Phys. Rev. Lett. 135, 086702 (2025) (arXiv)