Bilayer graphene interface with a Quantum Twisting Microscope

Abstract

Moiré physics, which studies the novel properties that arise when two or more 2D crystals are stacked with a twist between their layers, has unveiled unique electronic, optical, and mechanical properties, revolutionizing condensed matter physics. This thesis explores the use of the Quantum Twisting Microscope (QTM) to investigate the electronic properties of twisted bilayer graphene with in-situ control over the twist angle. The QTM is a novel scanning probe that enables dynamic rotation of 2D crystals, something unachievable before the development of the technique. The primary objective of the current work is to demonstrate our QTM’s capabilities in conducting in-situ twistronics experiments and detail the fabrication methods required for it. The experimental setup includes our own QTM which is created by adapting a commercial Atomic Force Microscope (AFM). The main modifications are a unique van der Waals tip and a modified sample stage that allows for twist angle control between the tip and sample. Our experience has demonstrated the importance of maintaining high quality standards in the fabrication of tips and samples to ensure succesful experiments. The main result of this thesis is the development of the fabrication techniques needed to achieve highly-clean surfaces in both parts of the QTM. This achievement has allowed us to reproduce previously reported behavior of the conductance across a twisted bilayer graphene interface. The successful implementation of our setup demonstrates its potential as a powerful tool for exploring moiré physics and engineering novel quantum states in 2D materials.