The magnetothermoelectric properties of three-dimensional Dirac/Weyl semimetals

The three-dimensional Dirac and Weyl semimetals can exhibit thermoelectric properties that are not possible in conventional metals and semiconductors. In this talk I give an overview of some of these properties, focusing in particular on the enhancement of thermopower by magnetic field. In single-band Dirac/Weyl materials, the thermopower rises linearly with magnetic field strength once the field is strong enough to achieve the extreme quantum limit, in which only the lowest Landau level is occupied. This enhancement can be viewed as the product of a "quantized" plateau in the thermoelectric Hall conductivity. In compensated systems, for which a pocket of electron-type carriers is almost completely compensated by a pocket of hole-type carriers, the field enhancement of thermopower is even sharper, growing quadratically with magnetic field beginning at a much lower value of field strength. I discuss these ideas in light of recent experiments on the three-dimensional Dirac semimetal ZrTe₅ and the compensated Weyl semimetal TaP.