Band Structure Engineering of 2D Materials using Patterned Dielectric Superlattices (1710.01365v2)

Abstract: The ability to manipulate two-dimensional (2D) electrons with external electric fields provides a route to synthetic band engineering. By imposing artificially designed and spatially periodic superlattice (SL) potentials, 2D electronic properties can be further engineered beyond the constraints of naturally occurring atomic crystals. Here we report a new approach to fabricate high mobility SL devices by integrating surface dielectric patterning with atomically thin van der Waals materials. By separating the device assembly and SL fabrication processes, we address the intractable tradeoff between device processing and mobility degradation that constrains SL engineering in conventional systems. The improved electrostatics of atomically thin materials moreover allows smaller wavelength SL patterns than previously achieved. Replica Dirac cones in ballistic graphene devices with sub 40nm wavelength SLs are demonstrated, while under large magnetic fields we report the fractal Hofstadter spectra from SLs with designed lattice symmetries vastly different from that of the host crystal. Our results establish a robust and versatile technique for band structure engineering of graphene and related van der Waals materials with dynamic tunability.

Band Structure Engineering of 2D Materials via Patterned Dielectric Superlattices

The paper discusses a methodological advancement in manipulating the electronic band structure of two-dimensional (2D) materials by employing patterned dielectric superlattices. Specifically, the focus is on using these superlattices to engineer the band structure of graphene and related van der Waals materials, featuring high mobility and dynamic tunability. This approach addresses key technical challenges traditionally associated with superlattice (SL) engineering.

Methodological Approach

The authors introduce a novel technique integrating patterned dielectric interfaces with atomically thin 2D materials, like graphene, through van der Waals heterostructures (vdW). In conventional SL engineering, remote electrostatic modulation was commonly employed via spatially patterned gate electrodes or donor layers. In contrast, this paper utilizes a featureless gate electrode while modulating the dielectric interface near the 2D electron gas (2DEG). This inversion provides advantages such as sharper electrostatic boundaries defined by the encapsulating dielectric, and a separation between PDSL and device fabrication processes, facilitating independent optimization before integration.

The research demonstrates fabrication of sub-40 nm wavelength SLs with high mobility, showcasing replica Dirac cones in ballistic graphene devices. It further explores fractal Hofstadter spectra in the presence of spatially periodic SL potentials with distinct lattice symmetries from the host graphene. The results confirm enhanced resolution capacity compared to lithographic patterning limitations in conventional systems, and address the tradeoff between processing and electron mobility.

Experimental Findings

Transport measurements and scanning tunneling microscopy (STM) outline the ability to observe and manipulate SL Dirac peaks and associated resistance features. At large magnetic fields, Hofstadter mini-gaps are realized, distinctly showcasing the synthetic band structure engineering potential of the approach. The research highlights electron-hole asymmetry in the band structure affecting transport responses and reveals the influence of SL lattice symmetry on magnetotransport characteristics.

Experiments under varying superlattice gate biases demonstrate the capability of dynamically tuning band structures. This is prominently observed when analyzing magnetoresistance within the quantum Hall effect regime, revealing a satellite fan structure centered around the SL Brillouin zone boundary.

Implications and Future Directions

The research offers substantive implications in the domain of synthetic band structure engineering. By utilizing patterned dielectric superlattices, the technique provides robust, versatile methodologies to manipulate 2D electronic band structures beyond naturally constrained atomic crystals. Practical applications could include precision tuning of electronic properties across various 2D materials, offering enhanced control over electronic and optoelectronic device functionalities.

Theoretically, these findings could catalyze further exploration of novel electronic phenomena emerging from engineered SL potentials and advancing the understanding of 2D material interactions. The future of AI developments lies in further integrating these patterned dielectric superlattices within complex vdW heterostructures, potentially uncovering new quantum states and diverse applications in electronic materials design.