Single-Carrier Transport in Graphene/hBN Superlattices

De Haas-van Alphen spectroscopy and magnetic breakdown in moiré graphene

Quantum oscillations originating from the quantization of electron cyclotron orbits provide sensitive diagnostics of electron bands and interactions. We report on nanoscale imaging of the thermodynamic magnetization oscillations caused by the de Haas-van Alphen effect in moiré graphene. Scanning by means of superconducting quantum interference device (SQUID)-on-tip in Bernal bilayer graphene crystal axis-aligned to hexagonal boron nitride reveals large magnetization oscillations with amplitudes reaching 500 Bohr magneton per electron in weak magnetic fields, unexpectedly low frequencies, and high sensitivity to superlattice filling fraction. The oscillations allow us to reconstruct the complex band structure, revealing narrow moiré bands with multiple overlapping Fermi surfaces separated by unusually small momentum gaps. We identified sets of oscillations that violate the textbook Onsager Fermi surface sum rule, signaling formation of broad-band particle-hole superposition states induced by coherent magnetic breakdown.

Developing Graphene-Based Moiré Heterostructures for Twistronics

Graphene-based moiré heterostructures are strongly correlated materials, and they are considered to be an effective platform to investigate the challenges of condensed matter physics. This is due to the distinct electronic properties that are unique to moiré superlattices and peculiar band structures. The increasing research on strongly correlated physics via graphene-based moiré heterostructures, especially unconventional superconductors, greatly promotes the development of condensed matter physics. Herein, the preparation methods of graphene-based moiré heterostructures on both in situ growth and assembling monolayer 2D materials are discussed. Methods to improve the quality of graphene and optimize the transfer process are presented to mitigate the limitations of low-quality graphene and damage caused by the transfer process during the fabrication of graphene-based moiré heterostructures. Then, the topological properties in various graphene-based moiré heterostructures are reviewed. Furthermore, recent advances regarding the factors that influence physical performances via a changing twist angle, the exertion of strain, and regulation of the dielectric environment are presented. Moreover, various unique physical properties in graphene-based moiré heterostructures are demonstrated. Finally, the challenges faced during the preparation and characterization of graphene-based moiré heterostructures are discussed. An outlook for the further development of moiré heterostructures is also presented.

Localization to delocalization probed by magnetotransport of hBN/graphene/hBN stacks in the ultra-clean regime

We report on magnetotransport in a high-quality graphene device, which is based on monolayer graphene (Gr) encapsulated by hexagonal boron nitride (hBN) layers, i.e., hBN/Gr/hBN stacks. In the vicinity of the Dirac point, a negative magnetoconductance is observed for high temperatures >  ~ 40 K, whereas it becomes positive for low temperatures ≤  ~ 40 K, which implies an interplay of quantum interferences in Dirac materials. The elastic scattering mechanism in hBN/Gr/hBN stacks contrasts with that of conventional graphene on SiO₂, and our ultra-clean graphene device shows nonzero magnetoconductance for high temperatures of up to 300 K.

Bloch oscillations at room temperature in graphene/h-BN electrostatic superlattices

In this manuscript, we report the fabrication and the measurements of Bloch oscillations at room temperature in electrostatic graphene/h-BN superlattices. The electrostatic superlattice consists of an array of tilted metallic electrodes deposited over graphene monolayer/h-BN monolayer grown on 2 inch wafers of doped Si/SiO₂. We show the formation of minibands at room temperature, negative differential resistance and the evidence of Bloch oscillations. The experimental results are sustained by numerical modelling of these 2D superlattices. The experimental results are sustained by numerical modelling of these 2D superlattices. At room temperature, we have measured a period of Bloch oscillations of 55 meV which corresponds to a frequency of 13 THz.