Transport phenomena in single crystal superconducting niobium

Abstract Following recent interest in niobium as a superconducting detector for possible astronomical dark matter, we have extended previous measurements of phonon propagation in high purity single crystal niobium below 1K. We have also, for the first time, observed the propagation of quasiparticles in bulk niobium, with a characteristic diffusion time an order of magnitude slower than that of the phonons.