Anomalous transport in metallic unconventional clathrate BaNi2P4

The mechanism of anomalous electronic transport in metallic unconventional clathrate BaNi2P4 was studied following the evolution of the temperature-dependent resistivity of single crystals of the title compound with artificial disorder induced by low-temperature (20 K) 2.5 MeV electron irradiation. The tetragonal-orthorhombic transition at Ts=378 K has a major impact on temperature-dependent resistivity, with standard metallic T-linear resistivity above the transition in the tetragonal phase and anomalous behavior in the low-temperature orthorhombic phase. The transition is accompanied by a notable hysteresis in the measured magnetization. The Matthiessen rule is obeyed both above and below the transition, suggesting negligible changes in the electronic structure. This conclusion is supported by the smooth evolution of the Hall resistivity through the transition. Unlike conventional structural transitions, the transition here is prone to disorder with the transition temperature notably suppressed with electron irradiation. A possibility of charge density wave associated with structural transition will be discussed.