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Public Seminar of PhD Candidate: Band structure engineering of 2D materials using designer superlattice potentials

Speaker Mr. Tianyu ZHANG
Affiliation The University of Hong Kong
Date August 27, 2024 (Tuesday)
Time 10:30 a.m.
Venue Room 522, 5/F, Chong Yuet Ming Physics Building, The University of Hong Kong

Abstract

Advances in van der Waals (vdW) assembly have enabled the construction of superlattices from 2D materials, tailoring their quantum properties. These superlattices arise from moiré patterns formed by similar or dissimilar materials, or from external perturbations such as strain or engineered patterns. The absence of dangling bonds in 2D materials enhances interfacial interactions, enabling precise tuning of electronic band structures. In this work, we investigate novel superlattice structures and their impact on graphene bands. We demonstrate that engineered hBN interfaces induce both moiré potentials and an unconventional ferroelectric effect. Near 1° parallel twisted hBN interfaces generate moiré patterns with wavelengths larger than those in traditional hBN/graphene systems. Electrical transport measurements reveal multiple satellite Dirac peaks, Hofstadter butterfly signatures, and Brown-Zak oscillations. In double bilayer hBN, we observe an unconventional ferroelectric behavior, including resistance hysteresis and a novel electronic ratchet effect. We also develop an optical method that combines optical contrast microscopy and second harmonic generation to accurately determine hBN layer numbers, critical for fabricating superlattices in different stacking configurations. Our findings reveal new phenomena at hBN interfaces, with graphene as a detector, suggesting potential for extending these studies to other 2D materials. This work contributes to understanding moiré physics, offering insights into the electronic properties of layered structures for both technological applications and fundamental research.
 

Anyone interested is welcome to attend.