Thermoelectrics in Future Information Technologies - Towards Zero-Power Systems

Methods for Characterization of Transport Phenomena in Energy Materials: Controlling collective states

Investigators: Dr. Katharina Fritsch, Dr. Tommy Hofmann, Dr. Klaus Habicht 
Thermoelectric devices are of central importance in creating new and more energy-efficient information technologies. The ultimate limits on the thermopower figure of merit of relevant materials are governed by the charge carrier densities and mobilities as well as phonon conduction. A basic understanding of the microscopic mechanisms is an inevitable prerequisite for well-targeted design strategies to develop materials with the efficiencies capable of addressing heat recovery and spot cooling applications.
Fundamental research on the interaction processes on the level of elementary excitations in the solid state and thus access to the meV to µeV energy resolution scale is key to a fundamental understanding of transport phenomena. The working group “Methods for Characterization of Transport Phenomena in Energy Materials” holds specialised expertise in high-resolution neutron spectroscopy well suited for investigating the dynamic interplay of quasi-particle and charge transport in novel materials for energy conversion. In particular, neutron resonance spin echo (NRSE) spectroscopy allows highest energy resolution for the investigation of elementary excitations in solid state matter and thus provides access to qualitatively new information about the lifetime of quasi particles and lattice anharmonicity. Interactions with other quasi particles or coherent many-body states display a fingerprint in the dynamical correlations, e.g. allowing the identification of lifetime reduction. Investigations on dispersive modes as they in general exist in single crystals, profit extraordinarily from the NRSE method. In the past, essential contributions to the development of the NRSE method for the investigation of excitations in the solid state have been made at HZB. The methodological progress made now allows accessing the fundamentals of transport phenomena which are at the basis of thermoelectrics.

The use of spin entropy based cooling where high densities of spin-disordered carriers present the prospect of much higher figures of merit. Important materials include 2D metallic systems such as triangular cobaltates, new pnictides, and narrow band heavy fermion compounds. Crucial here  is the use of inelastic neutron and X-ray scattering as well as angle resolved photoemission techniques in order to understand thoroughly the basic phonon, spin, and charge processes involved in the transport mechanisms and how these relate to the figures of merit. We intend to look at the materials both in single crystal form as well as in layered structures to understand both the principles underlying their operation as well as their functionalization.