Unveiling the Miniband Structure of Graphene Moiré Superlattices via Gate-dependent Terahertz Photocurrent Spectroscopy

Abstract

Moiré superlattices formed at the interface between stacked two-dimensional atomic crystals offer limitless opportunities to design materials with widely tunable properties and engineer intriguing quantum phases of matter. However, despite progress, precise probing of the electronic states and tantalizingly complex band textures of these systems remain challenging. Here, we present gate-dependent terahertz photocurrent spectroscopy as a robust technique to detect, explore and quantify intricate electronic properties in graphene moiré superlattices. Specifically, using terahertz light at different frequencies, we demonstrate distinct photocurrent regimes evidencing the presence of avoided band crossings and tiny (~1-20 meV) inversion-breaking global and local energy gaps in the miniband structure of minimally twisted graphene and hexagonal boron nitride heterostructures, key information that is inaccessible by conventional electrical or optical techniques. In the off-resonance regime, when the radiation energy is smaller than the gap values, enhanced zero-bias responsivities arise in the system due to the lower Fermi velocities and specific valley degeneracies of the charge carriers subjected to moiré superlattice potentials. In stark contrast, above-gap excitations give rise to bulk photocurrents -- intriguing optoelectronic responses related to the geometric Berry phase of the constituting electronic minibands. Besides their fundamental importance, these results place moiré superlattices as promising material platforms for advanced, sensitive and low-noise terahertz detection applications.

6 figures

References in corpus (15)

• Emergence of Superlattice Dirac Points in Graphene on Hexagonal Boron Nitride
• Graphene field effect transistors as room-temperature Terahertz detectors
• Fast pick up technique for high quality heterostructures of bilayer graphene and hexagonal boron nitride
• Electronic properties of graphene hexagonal boron nitride moiré superlattice
• Hierarchy of Hofstadter states and replica quantum Hall ferromagnetism in graphene superlattices
• Optical properties of graphene antidot lattices
• Edge currents shunt the insulating bulk in gapped graphene
• Moiré band model and band gaps of graphene on hexagonal boron nitride
• Room-Temperature Plasmon-Assisted Resonant THz Detection in Single-layer Graphene Transistors
• Band structure and gaps of triangular graphene superlattices
• Transport and particle-hole asymmetry in graphene on boron nitride
• Generation and morphing of plasmons in graphene superlattices
• Accurate Measurement of the Gap of Graphene/hBN Moiré Superlattice through Photocurrent Spectroscopy
• Atomic configuration controlled photocurrent in van der Waals homostructures
• Impact of Device Resistances in the Performance of Graphene-based Terahertz Photodetectors