Speaker
Aharon Kapitulnik
(Stanford)
Description
The Boltzmann-Drude picture of electronic transport ceases
to be valid when the electron mean-free-path becomes shorter
than the Fermi wavelength. The Mott-Ioffe-Regel limit is
defined where the two lengths are equal, and beyond it
metallic transport becomes incoherent. Most experimental
works have focused on the electronic transport, with the
host crystal providing a phonon background. Here we report
thermal diffusivity measurements that, together with the
resistivity, give a full account of transport of charge and
entropy. Utilizing a high-resolution photothermal apparatus,
we study the thermal diffusivity of several cuprate systems
in the regime where the quasiparticle picture fails for both
electron and phonons. The inverse diffusivity at high
temperature can be fitted with a temperature-linear form,
where the slope term is set by a unique velocity and a
Planckian relaxation time ~h/kBT, The constant term
represents a quantum-diffusion constant separating
incoherent transport from a regime with well-defined
quasiparticles.
