2, IBM, Zürich, , Switzerland
3, Max Planck Institute for Chemical Physics of Solids, Dresden, , Germany
Research in thermoelectric quantum structures was greatly powered by the prediction of a significant boost of the thermoelectric efficiency by quantum size effects in the early 90ies. Recently the research interest shifted from quantum size effects in trivial semiconductors towards new types of quantum materials, i.e. topological insulators (TI), Weyl and Dirac semimetals, characterized by their non-trivial electronic topology. Bi2Te3, Sb2Te3 and Bi2Se3, established thermoelectric materials, are also TIs exhibiting a bulk band gap and highly conductive and robust gapless surface states. The signature of the non-trivial electronic band structure on the thermoelectric transport properties can be best verified in transport experiments using nanowires and thin films. In that cases a two channel transport model could accout for the observed thermoelectric behaviour . But even in nanograined bulk, the typical peculiarities in the transport properties of TIs can be seen , evidencing potential for enhancement of the thermoelectric performance of materials. Finally, Dirac and Weyl semimetals [3,4,5], as for instance Bi1-xSbx, TaAs, NbP, or Cd3As2, are two recently discovered classes of 3-dimensional topological materials in which conduction and valence bands touch linearly close to the Fermi energy. This has revitalized the interest in Weyl fermions that were first discovered in high energy experiments. The investigation of the thermoelectric transport properties of Weyl semimetals currently opens the door for an advanced understanding of these exotic states of matter in which even the Ohm's law is fundamentally violated.
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