title: Low-dimensional transport and large thermoelectric power factors in bulk semiconductors by band engineering of highly directional electronic states.
abstract: Thermoelectrics are promising for addressing energy issues but their exploitation is still hampered by low efficiencies. So far, much improvement has been achieved by reducing the thermal conductivity but less by maximizing the power factor. The latter imposes apparently conflicting requirements on the band structure: a narrow energy distribution and a low effective mass. Quantum confinement in nanostructures and the introduction of resonant states were suggested as possible solutions to this paradox, but with limited success. Here, we propose an original approach to fulfill both requirements in bulk semiconductors. It exploits the highly directional character of some orbitals to engineer the band structure and produce a type of low-dimensional transport similar to that targeted in nanostructures, while retaining isotropic properties. Using first-principle calculations, the theoretical concept is demonstrated in Fe2YZ Heusler compounds, yielding power factors 4 to 5 times larger than in classical thermoelectrics at room temperature. Our findings are totally generic and rationalize the search of alternative compounds with similar behavior. Beyond thermoelectricity, these might be relevant also in the context of electronic, superconducting, or photovoltaic applications.
authors.affiliation: Theoretical Materials Physics, Université de Liège, 4000 Sart Tilman, Belgium.|Molecular and Biomolecular Physics Department, National Institute for Research and Development of Isotopic and Molecular Technologies, RO-400293 Cluj-Napoca, Romania.
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Bilc
authors.affiliation: Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, 1348 Louvain-la-neuve, Belgium.
authors.forename: Geoffroy
authors.initials: G
authors.lastname: Hautier
authors.affiliation: Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, 1348 Louvain-la-neuve, Belgium.
authors.forename: David
authors.initials: D
authors.lastname: Waroquiers
authors.affiliation: Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, 1348 Louvain-la-neuve, Belgium.
authors.forename: Gian-Marco
authors.initials: GM
authors.lastname: Rignanese
authors.affiliation: Theoretical Materials Physics, Université de Liège, 4000 Sart Tilman, Belgium.
authors.forename: Philippe
authors.initials: P
authors.lastname: Ghosez