Contact

    Claudia Felser, Prof. Dr.
    Phone: +49 351 4646-3004
    Fax: +49 351 4646-3002
    Kornelius Nielsch, Prof. Dr.
    Phone: +49 351 4659-102
    Fax: +49 351 4659-541

    Thermoelectric Properties of Weyl-Semimetals

    Topological insulators, Dirac semimetals and most recently Weyl semimetals (WSM) are the subject of considerable research interest in both fundamental physics and with respect to applications. The band structure of a WSM exhibits a crossing of two bulk bands, which results in two so-called Weyl points with opposing parity. These pairs are expected to be notably robust but are only realized in 3D systems, where either time-reversal or inversion symmetry is broken. Therefore, weyl semimetals are often considered the 3D-analogon of graphene or topological insulators. The evaluation of quantum oscillations in these systems remains challenging because there are often multiple conduction bands.

    Beside very fascinating physical effect, like e.g. chiral magnetoresistance, the materials also exhibit significant thermovoltages and thermoelectric power factor, which can be strongly modulated under the influences of magnetic field. In this Ph.D. project single crystals with micrometer size will be lithographically contacted and the thermoelectric transport properties will be measured under the influence of magnetic fields over a wide temperature range 300 mK to 500 K. A number of Weyl semimetals like NbP, TaAf, HfTe5 will be measured and analyzed with a strong theoretical support. Based on the most promising Weyl semimetals for thermoelectric application a thermoelectric demonstrator could be developed in the framework of this Ph.D. project.

    <p>(<strong>a</strong>) Sketch of a Weyl semimetal, represented as two spatially separated, massless Weyl nodes with distinct chiralities χ = −1 (red cone) and +1 (blue cone). (<strong>b</strong>) The non-centrosymmetric crystal structure in a tetragonal lattice (space group <em>I</em><sub>4</sub>1<em>md</em>) of NbP and (<strong>c</strong>) the XRD spectrum with a logarithmic intensity scale of the bulk NbP measured at room temperature. (<strong>d</strong>) Optical micrograph of the NbP micro-ribbon, which has been defined by Ga-FIB. (<strong>e</strong>) SEM-EDX data of the first 3 μm from the left sample edge along the [100] direction of the NbP micro-ribbon reveals an average 53% Nb, 45% P and 2% Ga composition. (<strong>f</strong>) Plot of the resistivity <em>ρ</em> versus temperature <em>T</em></p> Zoom Image

    (a) Sketch of a Weyl semimetal, represented as two spatially separated, massless Weyl nodes with distinct chiralities χ = −1 (red cone) and +1 (blue cone). (b) The non-centrosymmetric crystal structure in a tetragonal lattice (space group I41md) of NbP and (c) the XRD spectrum with a logarithmic intensity scale of the bulk NbP measured at room temperature. (d) Optical micrograph of the NbP micro-ribbon, which has been defined by Ga-FIB. (e) SEM-EDX data of the first 3 μm from the left sample edge along the [100] direction of the NbP micro-ribbon reveals an average 53% Nb, 45% P and 2% Ga composition. (f) Plot of the resistivity ρ versus temperature T

     
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