Tomonaga-Luttinger liquid in the edge channels of a quantum spin Hall insulator

Quantum spin Hall insulators are two-dimensional materials that host conducting helical electron states strictly confined to the one-dimensional boundaries. These edge channels are protected by time-reversal symmetry against single-particle backscattering, opening new avenues for spin-based electronics and computation. However, the effect of the interelectronic Coulomb repulsion also has to be taken into account, as two-particle scattering is not impeded by topological protection and may strongly affect the edge state conductance. Here, we explore the impact of electronic correlations on highly localized edge states of the unique quantum spin Hall material bismuthene on SiC(0001) (ref. (1)). Exploiting the advantage of having an accessible monolayer substrate system, we use STM/STS to visualize the close-to-perfect one-dimensional confinement of the edge channels and scrutinize their suppressed density of states at the Fermi level. On the basis of the observed spectral behaviour and its universal scaling with energy and temperature, we demonstrate the correspondence with a (helical) Tomonaga-Luttinger liquid. In particular, the extracted interaction parameter K is directly relevant to the fundamental question of the temperatures at which the quantized conductance (a hallmark of quantum spin Hall materials) will become obscured by correlations(2). Scanning tunnelling microscopy and spectroscopy study of the conductive edge state in a two-dimensional topological insulator reveals the interplay of topology and electronic correlations.