2025/01/14 by Smith, E. M., Fitterman, A., Schäfer, R. +18 · 6 citations
#FOS: Physical sciences #Strongly Correlated Electrons (cond-mat.str-el)
paper · doi:10.48550/arxiv.2501.08327
Magnetic heat capacity measurements of a high-quality single crystal of the dipole-octupole pyrochlore Ce2Hf2O7 down to a temperature of T = 0.02 K are reported. These show a two-peaked structure, with a Schottky-like peak at T1 ∼ 0.065 K, similar to what is observed in its sister Ce-pyrochlores Ce2Zr2O7 and Ce2Sn2O7. However, a second sharper peak is observed at T2 ∼ 0.025 K, signifying the entrance to the ground state. The ground state appears to have gapped excitations, as even the most abrupt extrapolation to CP=0 at T = 0 K fully accounts for the Rln(2) entropy associated with the pseudospin-1/2 doublet for Ce3+ in this environment. The ground state could be conventionally ordered, although theory predicts a much larger anomaly in CP at much higher temperatures than the measured T2 for expectations from an all-in all-out ground state of the XYZ Hamiltonian for Ce2Hf2O7. The sharp low-temperature peak could also signify a cross-over from a classical spin liquid to a quantum spin liquid (QSL). For both scenarios, comparison of the measured CP with NLC calculations suggests that weak interactions beyond the nearest-neighbor XYZ Hamiltonian become relevant below T ∼ 0.25 K. The diffuse magnetic neutron scattering observed from Ce2Hf2O7 at low temperatures between T2 and T1 resembles that observed from Ce2Zr2O7, which is well established as a π-flux quantum spin ice (QSI). Together with the peak in the heat capacity at T2, this diffuse scattering from Ce2Hf2O7 is suggestive of a classical spin liquid regime above T2 that is distinct from the zero-entropy quantum ground state below T2.