Conductivity of charge-neutral multicomponent 2D electron-hole system

Abstract

The interplay between distinct carrier species in systems with broken Galilean invariance can give rise to a rich landscape of interaction-driven transport phenomena. Here, we develop a comprehensive theory for the electrical conductivity of a two-dimensional mixture of massless Dirac and massive fermions, a system realized in HgTe quantum wells tuned to the charge neutrality point. In this regime, all carriers are thermally activated, enabling a self-consistent, temperature-dependent interplay between the two species. Crucially, the charge neutrality condition ensures that the chemical potential is not externally pinned but is determined self-consistently, making the system's transport response an intrinsic probe of inter-species quantum friction. We demonstrate that the conductivity undergoes a distinct crossover as temperature increases: at low temperatures, transport is dominated by massless Dirac carriers, yielding nearly temperature-independent conductivity reminiscent of pristine graphene's charge neutrality point. As the temperature rises, massive holes become thermally excited, and their mutual scattering with Dirac carriers induces a specific nonmonotonic temperature behavior of the conductivity both in clean and disordered structures. In particular, in nearly clean structures with strong screening modeled by a short-range interparticle interaction potential, the system conductivity can exhibit an inverse quadratic temperature dependence. Conversely, in disordered structures with a long-range interparticle interaction, it varies quadratically with temperature. Our findings establish HgTe quantum wells at charge neutrality as a clean, highly tunable platform for isolating and quantitatively studying interaction-driven transport in the absence of Galilean invariance, offering a direct pathway to explore regimes where interparticle collisions dominate over disorder.