Charge transport in two-dimensional conductors with hybrid three-component plasma

Electron--hole plasma in two-dimensional solid-state systems has previously been studied mainly in two limiting cases: the degenerate regime in semimetals with parabolic bands, and the nondegenerate symmetric Dirac regime in graphenelike materials. Here we investigate a third, qualitatively different case realized in a gapless HgTe quantum well: a multicomponent plasma with a hybrid spectrum, in which massless Dirac carriers coexist with thermally activated heavy holes from lateral valence-band valleys. Near the charge-neutrality point we observe a pronounced increase of the resistance with temperature, following an approximately ${T}^{2}$ law, in sharp contrast to the nearly temperature-independent resistivity expected for a symmetric two-component Dirac plasma. We show that this behavior originates in the charge-neutrality condition, which, once the heavy holes are populated, pins the chemical potential above the Dirac point: the Dirac electrons remain moderately degenerate, while the heavy holes stay nondegenerate and obey Boltzmann statistics. Because the light degenerate electrons scatter almost elastically off the heavy Boltzmann holes, the interparticle transport admits a relaxation-time description and can be treated nonperturbatively. Using carrier densities from self-consistent band structure calculations, we find that the data are well reproduced by a short-range interaction between Dirac electrons and heavy holes in the weakly disordered limit for which the electronic conductivity scales as ${T}^{\ensuremath{-}2}$ and the excess resistivity is proportional to the heavy-hole density, whereas an unscreened Coulomb interaction would leave the conductivity temperature independent. The extracted interaction amplitude is of the Coulomb scale expected at the low charge-neutrality density. Our results establish near-critical HgTe quantum wells as a versatile platform for studying interaction-driven transport in multicomponent systems combining degenerate massless and nondegenerate massive carriers in which the linear Dirac spectrum decouples the current from the total momentum.