Probing interactions with thermal transport

Thermal and thermoelectric conductivities are ideal probes of interaction effects in

correlated electron systems.  This is because, in contrast to an electric current,  a heat current can be transmitted also by neutral quasiparticles. For instance, energy can be carried by excitations that mediate interactions between other quasiparticles. 

In my talk I will present two examples of the dramatic effect of interactions on thermal and thermoelectric transport phenomena.  The first is the Nernst effect in the vicinity of the superconducting phase transition. I will demonstrate that the giant Nernst signal, experimentally observed in amorphous films far above Tc, is caused by the fluctuations of the superconducting order parameter. Moreover, I will discuss the anomalous behavior of the Nernst effect near the magnetic-field-induced quantum critical phase transition. The second example is thermal conductivity in spin liquids. Spin liquids can form in the vicinity of the Mott metal-insulator transition when the charge is gapped while the spin degrees of freedom strongly fluctuate. These low energy excitations, dubbed spinons, can conduct heat. The spinons also exhibit a magnetic interaction that leads to non-Fermi liquid behavior. I will show that even in the absence of disorder this strong interaction provides an efficient relaxation mechanism for heat and spin currents, keeping them finite at the lowest temperatures.