Abstract

The Mott formula connects the energy derivative of the electrical conductivity with the thermopower. This forms the basis of our interpretation of thermopower measurements in the Fermi liquid state at low temperatures. Thermoelectric transport measurements therefore access not only properties of the Fermi surface but also their energy dependence.

I will present new measurements of the thermoelectric power at low temperature in magnetic fields up to 12T on the well known heavy fermion materials CeRu2Si2 and YbRh2Si2. In both of these materials, a metamagnetic transition occurs at around 10T. I will discuss the possible origins of metamagnetism in each case and show why the thermopower is a valuable probe that can be more sensitive to Fermi surface changes than other transport properties, and what conclusions we can draw from successes and failures of the Mott formula.