# Phase-coherent loops in selectively-grown topological insulator nanoribbons

## TL;DR

This study demonstrates that conductance fluctuations in selectively-grown topological insulator nanoribbons originate from well-defined phase-coherent loops, revealing their orientation and phase-coherence lengths through experimental and theoretical analysis.

## Contribution

It provides direct experimental evidence linking conductance fluctuations to specific phase-coherent loops in topological insulator nanoribbons and analyzes their orientation and coherence properties.

## Key findings

- Conductance fluctuations are caused by well-defined phase-coherent loops.
- Loops are oriented parallel to the quintuple layers.
- Phase-coherence length is larger from universal conductance fluctuations than from weak antilocalization.

## Abstract

Universal conductance fluctuations and the weak antilocalization effect are defect structure specific fingerprints in the magnetoconductance that are caused by electron interference. Experimental evidence is presented that the conductance fluctuations in the present topological insulator (Bi$_{0.57}$Sb$_{0.43}$)$_2$Te$_3$ nanoribbons which are selectively grown by molecular beam epitaxy are caused by well-defined and sharply resolved phase-coherent loops. From measurements at different magnetic field tilt angles we deduced that these loops are preferentially oriented parallel to the quintuple layers of the topological insulator material. Both from a theoretical analysis of universal conductance fluctuations and from weak antilocalization measured at low temperature the electronic phase-coherence lengths $l_\phi$ are extracted, which is found to be larger in the former case. Possible reasons for this deviation are discussed.