Quantum spin Hall quantum point contacts

Quantum spin Hall insulators (QSHIs) provide helical, time reversal protected edge modes. When strongly localized and thus considerably one-dimensional, these edge states may be described in terms of helical Luttinger liquids. In that respect, especially the formation of interaction induced gaps is particularly exciting. Although the formation of the underlying scattering terms might be demanding for isolated helical edges, the situation shifts when both edges of the QSHI are brought in proximity to each other. Then, the increased number of channels enables a variety of scattering terms, all of which relevant even for weak repulsive Coulomb interactions. Indeed, very recent transport experiments on QSHI quantum point contacts not only imply the existence of interactions at the helical edge, but also indicate the presence of two-particle scattering terms. This is especially interesting, since these terms, among proximity induced superconductivity, constitute one brick for the construction of parafermionic excitations in the same system.