Transport in InAs/GaSb heterostructures with different InAs layer thicknesses is studied using a six-terminal Hall bar geometry with a 2-µm edge channel length. For a sample with a 12-nm-thick InAs layer, non-local resistance measurements with various current/voltage contact configurations reveal that the transport is dominated by edge channels with negligible bulk contribution. Systematic non-local measurements allow us to extract the resistance of individual edge channels, revealing sharp resistance fluctuations indicative of inelastic scattering. Our results show that the InAs/GaSb system can be tailored to have conducting edge channels while keeping a gap in the bulk region and provide a way of studying 2D topological insulators even when quantized transport is absent.

We report a gate-controlled transition of a semimetallic InAs/GaSb heterostructure to a topological insulator. The transition is induced by decreasing the degree of band inversion with front and back gate voltages. Temperature dependence of the longitudinal resistance peak shows the energy gap opening in the bulk region with increasing gate electric field. The suppression of bulk conduction and the transition to a topological insulator are confirmed by nonlocal resistance measurements using a dual lock-in technique, which allows us to rigorously compare the voltage distribution in the sample for different current paths without the influence of time-dependent resistance fluctuations.Topological insulators (TIs) have attracted strong interest as a new quantum state of matter categorized neither as a metal nor an insulator. 1-10 The unique electronic properties of TIs originate from their band structures characterized by conduction-valance band inversion with an energy gap opening in the bulk region. The band inversion results from the interplay between the alignment of bands with different orbital characters and the strong spin-orbit interaction inherent to materials containing heavy elements, such as Bi compounds 1-3 and HgTe. 7-10 Owing to their topological nature, gapless states with distinct transport characteristics emerge at the surfaces and edges of three-and two-dimensional (2D) TIs, respectively. In a 2D TI, also known as a quantum spin Hall insulator, the edge state comprises counterpropagating channels with opposite spin. 1,2,4-7 Since elastic back scattering is prohibited by time-reversal symmetry, dissipationless spin-polarized transport is expected. The observation of the quantum spin Hall effect in a HgTe/CdTe quantum well 8-10 has established it as a prototypical system for 2D TIs.

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ERGIC-53 and VIP36 are categorized as leguminous type (L-type) lectins, and they function as cargo receptors for trafficking certain N-linked glycoproteins in the secretory pathway in animal cells. They share structural similarities in their carbohydrate recognition domains (CRDs) but exhibit distinct sugar-binding specificities and affinities. VIP36 specifically interacts with the α1,2-linked D1 mannosyl arm without terminal glucosylation, while ERGIC-53 shows a broader specificity and lower binding affinity to the high-mannose-type oligosaccharides, irrespective of the presence or absence of the non-reducing terminal glucose residue at the D1 arm. In this study, we determined the crystal structure of ERGIC-53–CRD in complex with their binding partner, MCFD2 and the α1,2 mannotriose which corresponds to the trisaccharide of the D1 arm of high-mannose-type glycans. ERGIC-53 can interact with the D1 trimannosyl arm in two alternative modes, one of which is similar but distinct from that previously observed for VIP36. ERGIC-53 has a shallower sugar-binding pocket than VIP36 because of the single amino acid substitution, Asp-to-Gly. This enables ERGIC-53 to accommodate the non-reducing terminal glucose of the D1 arm in its CRD. In the other interaction mode, the 3-OH group of the terminal mannose was situated outward with respect to the sugar binding pocket, also enabling the Glcα1-3 linkage formation without steric hindrance. Our findings thus provide a structural basis for the broad sugar-binding specificity of the ERGIC-53/MCFD2 cargo receptor complex.