Investigation of the Planckian scattering rate in PdCrO₂ by high energy electron irradiation

PdCrO₂ belongs to the delafossite family of extremely pure triangular lattice metals. While its Pd layers are metallic, the CrO₂ layers are Mott insulating, and order antiferromagnetically below 37.5 K. PdCrO₂ therefore combines the opposite ends of possibilities for the motion of electrons in a solid: a nearly free electron metal and a Mott insulating state, forming an ideal platform to investigate the coupling between such disparate systems [1].

The resistivity of PdCrO₂ is linear in temperature above 150 K. This is in contrast to the non-magnetic sister compound PdCoO₂ indicating that it is a consequence of the coupling to the Mott-insulating layer. Intriguingly, in the region of the T-linear resistivity, the scattering rate per kelvin is well approximated by the ratio of fundamental constants, k_B/h. Numerous other materials reveal the same slope in the T-linear region, in spite of large differences in the microscopic origins of the scattering [2].

To investigate the universal behaviour of the scattering rate, we conducted a systematic study of the influence of point defects on the resistivity of PdCrO₂, the results of which we report here. We introduced point defects to focused ion beam sculpted microstructures of PdCrO₂ by irradiating them with high-energy electrons. Comparing the results with those on PdCoO₂, we confirm that the increase in the resistivity is dominated by point defects in conductive Pd layers. Matthiessen's rule is obeyed  in the a T-linear region, indicating the independence of the Planckian dissipation.

[1] Mackenzie, A.P., 2017. Rep. Prog. Phys. 80, 32501

[2] J. A. N. Bruin, H. Sakai, R. S. Perry and A. P. Mackenzie, 2013, Science, Vol 339, Issue 6121, pp. 804-807