Kinetics-Driven Selective Stoichiometric Shift and Structural Asymmetry in $Bi_4Te_3$ Nanostructures for Hybrid Quantum Architectures

TL;DR

This paper develops a precise MBE growth method for $Bi_4Te_3$ nanostructures, revealing a selective stoichiometric shift driven by adatom kinetics and structural asymmetry, advancing their integration into quantum devices.

Contribution

It introduces a reproducible MBE process for high-quality $Bi_4Te_3$ films and uncovers the coupling between adatom diffusion and nanoscale composition, along with intrinsic structural asymmetry.

Findings

Reproducible MBE growth of $Bi_4Te_3$ with atomically sharp interfaces.

Identification of selective stoichiometric shift due to adatom diffusion.

Discovery of structural asymmetry in van der Waals gaps.

Abstract

Advances in hybrid quantum architectures hinge on topological materials that can be synthesized with precise stoichiometric and structural control at the nanoscale. While $Bi_4Te_3$ is a promising candidate due to its dual topological phases, acting as both a strong topological insulator and a topological crystalline insulator, high-quality growth remains challenging due to a narrow stoichiometric window and high sensitivity to surface kinetics. Here, we establish a reproducible molecular beam epitaxy (MBE) process to produce stoichiometric, twin-free $Bi_4Te_3$ thin films with ultra-smooth surfaces and atomically sharp van der Waals stacks. By employing selective area epitaxy (SAE), we realize laterally confined $Bi_4Te_3$ nanostructures that exhibit a feature-dependent stoichiometric deviation. This phenomenon, which we term the selective stoichiometric shift, arises from the unequal lateral diffusion of Bi and Te adatoms, revealing a direct coupling between adatom kinetics and nanoscale compositional stability. Atomic-resolution imaging further uncovers asymmetric van der Waals gaps within the stacking sequence, identifying an intrinsic structural asymmetry between the quintuple and bilayer units. These findings provide fundamental insights into the crystallization of Bi_4Te_3$ and demonstrate a scalable route for integrating functional topological materials into next-generation superconducting hybrid quantum circuits.