Comparison of thermopower behaviour in different superconductors

Abstract

The in-plane normal-state thermoelectric power of the cuprate superconductors, like the resistivity and Hall angle, shows a remarkable systematic pattern as the hole concentration is decreased from the overdoped to the underdoped regime. In the overdoped regime where T C is reduced to small values, the cuprate thermopower is often approximately proportional to temperature, i.e. it resembles conventional metallic diffusion thermopower. Similar proportionality is seen in disordered metal, Chevrel-phase and fullerene superconductors (with a low-temperature anomaly ascribed to a strong electron-phonon interaction). As the hole concentration in the overdoped cuprates is decreased and T C increases to optimal values and then decreases again, there is an approximately temperature-independent shift of thermopower to more positive values. Surprisingly similar shifts are seen in more conventional superconductors such as NbN and Chevrel-phase compounds as the level of disorder is reduced.