Ultraclean graphene: from record mobility to suspended moiré superlattices
Abstract:
The quality of an electronic system, typically quantified by its mobility, doping homogeneity and, in moiré materials, twist-angle uniformity, determines the visibility and robustness of quantum phenomena. Since its discovery, graphene has been recognized as an exceptionally clean material with a vanishingly small number of intrinsic defects, yet realizing its intrinsic potential has remained challenging. In this talk, I will present three developments that overcome established limitations of van der Waals devices and open new routes for the exploration of electronic and structural phenomena.
First, I will describe graphene devices with engineered Coulomb screening, created either by proximal graphite gates or by encapsulating graphene between other graphene layers decoupled by a large twist angle. These devices yield mobilities up to 6 × 107 cm2 V-1 s-1, the highest reported for any material, and show how engineering the dielectric environment reveals electronic quality previously masked by extrinsic disorder.
Second, I will show how a related architecture allows us to probe and control interlayer hybridization in moiré systems. Although miniband formation is usually associated with twisted layers in direct contact, graphene layers separated by a monolayer spacer retain sufficient coupling to exhibit pronounced minibands and Brown-Zak oscillations, which can now be controlled by displacement field. The spacer also suppresses atomic reconstruction, yielding highly uniform twist angles over macroscopic distances, with twist-angle disorder of just ~0.01°. The same signatures appear in CVD-grown twisted structures, opening a route towards scalable long-period superlattices.
Third, I will address a long-standing bottleneck in heterostructure assembly: residual contamination from polymer-based stacking. Replacing standard polymer stamps with mica crystals yields devices with ultraclean surfaces and enables new architectures, including suspended twisted graphene superlattices. Atomic force microscopy reveals moiré buckling of 0.1-0.7 nm at the nodes of the domain-wall network, driven by relaxation toward low-energy stacking, while heterostrain induces crinkling along the domain walls. The transition between these regimes is highly sensitive to the magnitude and anisotropy of heterostrain, giving access to a rich family of moiré morphologies at fixed twist angle, and opening a promising direction for further research.
The quality of an electronic system, typically quantified by its mobility, doping homogeneity and, in moiré materials, twist-angle uniformity, determines the visibility and robustness of quantum phenomena. Since its discovery, graphene has been recognized as an exceptionally clean material with a vanishingly small number of intrinsic defects, yet realizing its intrinsic potential has remained challenging. In this talk, I will present three developments that overcome established limitations of van der Waals devices and open new routes for the exploration of electronic and structural phenomena.
First, I will describe graphene devices with engineered Coulomb screening, created either by proximal graphite gates or by encapsulating graphene between other graphene layers decoupled by a large twist angle. These devices yield mobilities up to 6 × 107 cm2 V-1 s-1, the highest reported for any material, and show how engineering the dielectric environment reveals electronic quality previously masked by extrinsic disorder.
Second, I will show how a related architecture allows us to probe and control interlayer hybridization in moiré systems. Although miniband formation is usually associated with twisted layers in direct contact, graphene layers separated by a monolayer spacer retain sufficient coupling to exhibit pronounced minibands and Brown-Zak oscillations, which can now be controlled by displacement field. The spacer also suppresses atomic reconstruction, yielding highly uniform twist angles over macroscopic distances, with twist-angle disorder of just ~0.01°. The same signatures appear in CVD-grown twisted structures, opening a route towards scalable long-period superlattices.
Third, I will address a long-standing bottleneck in heterostructure assembly: residual contamination from polymer-based stacking. Replacing standard polymer stamps with mica crystals yields devices with ultraclean surfaces and enables new architectures, including suspended twisted graphene superlattices. Atomic force microscopy reveals moiré buckling of 0.1-0.7 nm at the nodes of the domain-wall network, driven by relaxation toward low-energy stacking, while heterostrain induces crinkling along the domain walls. The transition between these regimes is highly sensitive to the magnitude and anisotropy of heterostrain, giving access to a rich family of moiré morphologies at fixed twist angle, and opening a promising direction for further research.
Practical information
- General public
- Free
Organizer
- Prof. Oleg Yazyev, Dr. Yaroslav Zhumagulov
Contact
- Yazyev Oleg <[email protected] > Zivkovic Ivica <[email protected] >