Charge and entropy transport in strontium titanate

The ferroelectric instability in pristine strontium titanate is aborted by quantum fluctuations. Therefore, the static electric permittivity saturates to an extremely large value at low temperature and the effective Bohr radius approaches a micron. In this context, removing a tiny fraction of oxygen atoms turns the system to a dilute metal with a sharp Fermi surface and a superconducting instability. The focus of this talk will be charge and entropy transport by electrons in this dilute metal and their broad implications.

The temperature dependence of the resistivity of this dilute metal at low temperature is quadratic, even though Umklapp scattering is absent and there is a single Fermi pocket is at the zone center. The prefactor of this T-square resistivity corresponds to what is expected in an extended Kadowaki-Woods scaling. In all known Fermi liquids, knowing the Fermi energy allows one to predict the rough magnitude of the T-square resistivity. The origin of this empirical rule, valid over 4 orders of magnitude, is not known.

At high temperature, on the other hand, the quasi-particle picture of transport in dilute metallic strontium titanate breaks up. The magnitude of resistivity leads to a mean-free-path too short to be plausible. The temperature dependence of the Seebeck coefficient implies that non-degenerate electrons are becoming heavier with warming. This points to a new route towards mass amplification through entropy accumulation. These observations appear to reside beyond available polaronic theories.

Host: Dmitrii Maslov