Herwig Michor, Andrei V. Ruban, Michele Reticcioli, Fabian Garmroudi, Takao Mori, Andrej Pustogow, Ernst Bauer, Matthias Knopf, Alexander Riss, Michael Parzer, and Sergii Khmelevskyi
Discovered exactly 200 years ago in 1821, thermoelectricity is nowadays of global interest as it allows to directly interconvert thermal and electrical energy via the Seebeck/Peltier effect, which could be exploited to enhance energy efficiency. In their seminal work, Mahan and Sofo mathematically derived the conditions for ’the best thermoelectric’ − a delta-distribution-shaped electronic transport function, where charge carriers contribute to transport only in an infinitely narrow energy interval. So far, however, only approximations to this concept were expected to really exist in nature. Here, we propose as a physical realisation of this scenario the Anderson transition in an impurity band, i.e. the transition from Anderson-localised to extended quantum states. We obtained a significant enhancement and dramatic change of the thermoelectric properties from p-type to n-type in the stoichiometric Heusler compound Fe2VAl, which we assign to a narrow region of delocalised electrons in the energy spectrum near the Fermi energy. We achieved this through an innovative approach of driving the Anderson transition via continuous disorder tuning: variable amounts of atomic defects are induced in a controlled fashion by thermal quenching from high temperatures (950 − 1380 °C). Based on our experimental electronic transport and magnetisation results, supported by Monte-Carlo and density functional theory calculations, we demonstrate a universal enhancement strategy towards colossal thermoelectric performance that is applicable to diverse material classes.