Energy relaxation of hot carriers near the charge neutrality point in HgTe-based 2D topological insulators

We present experimental results of non-linear transport in HgTe-based 2D topological insulators, where the conductance is dominated by Dirac-like helical edge states when the Fermi level is pinned to the bulk insulating gap. We find that hot carrier's energy relaxation is faster close to the charge neutrality point (CNP) which can be attributed to localized nature and incompressibility of charge puddles resulting from inhomogeneous charge distribution near CNP. The tunnel-coupling of these puddles (quantum dots) to 1D edge channels can randomize phase memory leading to incoherent inelastic processes. Hot edge carriers, excited by the electric field, relax to equilibrium via thermalization in multiple puddles resulting in the emission of phonons in the puddles. At relatively low temperature (T ≤ 10 K), the energy relaxation time shows strong temperature dependence (τε ∝ (Te−5)), which is interpreted as small angle scattering, consistent with resistance saturation at low temperatures. [Display omitted] •Electric field induced non-equilibrium phenomena in 2D topological insulators•Energy relaxation of hot carriers is possible only due to inelastic processes since the 1D edge channels are helical in nature.•Tunnel-coupling of 1D channels to charge puddles resulting from charge inhomogenity•Fast energy relaxation in multiple puddles close to CNP•Strong temperature dependence at relatively low temperatures