Chiral-helical junctions in screened graphene

TL;DR

This paper demonstrates robust quantized transport in a graphene quantum Hall topological insulator stabilized by metallic screening, enabling control over helical channels and advancing topological device potential.

Contribution

It introduces a method to achieve reproducible quantized transport in graphene topological insulators using metallic screening, and reveals mechanisms affecting quantization stability.

Findings

Quantized resistance plateaus achieved at low magnetic fields.

Gate-defined chiral-helical junctions enable mode control.

Contact-induced doping impacts quantization, mitigated by large area contacts.

Abstract

Reproducibility and quantization in quantum spin Hall platforms is a persisting challenge, limiting their use in hybrid realizations of topological superconductivity. We report robust and reproducible quantized transport in a graphene quantum Hall topological insulator, stabilized at low magnetic fields by screening long-range Coulomb interactions with a metallic Bi$_2$Se$_3$ back gate. Beyond quantized resistance plateaus, we demonstrate mode-resolved control via gate-defined chiral-helical junctions that selectively transmit or backscatter a single helical channel, a capability inaccessible in time-reversal symmetric quantum spin Hall systems. Targeted experiments and simulations identify contact-induced doping, effectively creating unintended chiral-helical interfaces, as a generic mechanism for quantization breakdown, which is mitigated by large area contacts that enhance edge-channel equilibration. Our findings establish metal screened graphene as a gate-tunable, interaction-driven helical system with quantized transport, spatially separable helical channels, and compatibility with superconducting proximity for topological devices.