Condensed Matter Theory

Abstract:

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 crossover 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.

Abstract:

We show that a suspension of noninteracting deformable particles subjected to an oscillatory shear flow leads to development of nematic order that arises from the phenomenon of phase synchronization. The synchronized state corresponds to a unique, stable limit cycle confined in the toroidal state space. The limit cycle exists since, unlike rigid particles, deformable particles can modulate aspect ratio, adjust their tumbling rate, and thus achieve phase synchronization. These synchronized regions emerge as Arnold tongues in the parameter space of the driving amplitude and frequency. Considering the rheological implications of ordering dynamics in soft and active matter, our results motivate oscillatory shear flow experiments with deformable particles.