Stepwise quantized surface states and delayed Landau level hybridization in Co cluster-decorated BiSbTeSe2 topological insulator devices

TL;DR

This paper demonstrates stepwise quantization of surface states in Co cluster-decorated BiSbTeSe2 topological insulators, revealing delayed Landau level hybridization and independent quantization of top and bottom surfaces, advancing topological device control.

Contribution

It introduces a method to achieve separate quantization of top and bottom surface states in TIs via Co cluster decoration, showing delayed Landau level hybridization.

Findings

Stepwise quantization of surface states observed.

Delayed Landau level hybridization due to Co clusters.

Distinct quantization trajectories for top and bottom surfaces.

Abstract

In three-dimensional topological insulators (TIs), the nontrivial topology in their electronic bands casts a gapless state on their solid surfaces, using which dissipationless TI edge devices based on the quantum anomalous Hall (QAH) effect and quantum Hall (QH) effect have been demonstrated. Practical TI devices present a pair of parallel-transport topological surface states (TSSs) on their top and bottom surfaces. However, due to the no-go theorem, the two TSSs always appear as a pair and are expected to quantize synchronously. Quantized transport of a separate Dirac channel is still desirable, but has never been observed in graphene even after intense investigation over a period of 13 years, with the potential aim of half-QHE. By depositing Co atomic clusters, we achieved stepwise quantization of the top and bottom surfaces in BiSbTeSe2 (BSTS) TI devices. Renormalization group flow diagrams13, 22 (RGFDs) reveal two sets of converging points (CVPs) in the (Gxy, Gxx) space, where the top surface travels along an anomalous quantization trajectory while the bottom surface retains 1/2 e2/h. This results from delayed Landau-level (LL) hybridization (DLLH) due to coupling between Co clusters and TSS Fermions.