The observation of correlated states and superconductivity in twisted trilayer graphene

Credit: Zhang et al.
Two layers of graphene, or other two-dimensional (2D), materials are placed on top of one another with slight angle misalignment. This causes crystal lattices to be spatially out of synch. This creates a unique structural pattern called moir superlattice.

Many physicists have been studying the properties and characteristics moir superlattices in recent years. They have proven to be very promising for developing new quantum technologies. These studies have mainly focused on twisted bilayergraphene, which is composed of two layers of graphene that are stacked on top each other and rotated at a slight twist angle.

Harvard University and the University of Minnesota recently conducted a study on the properties of trilayer graphene twisted. This is composed of three layers of graphene stacked with two consecutive small twist angles. The paper was published in Physical Review Letters. It provides evidence of correlated superconductivity states and the transport signature.

Ke Wang, one the researchers behind the study, said that it was already demonstrated that twisted bilayer graphene could become superconducting by adjusting the twist angle. The twisted-bilayers can be highly tuned in terms of material parameters as well as electrostatics. This allows for new insights into correlated electron physics and promises new applications for quantum electronics.

Wang and his collaborators created a structure they called "moir of moir" superlattice by adding a third layer graphene. The structure was then studied and analyzed to understand its characteristics and properties.

Wang explained that "our recent work adds an additional layer of graphene in order to form a twist-trilayer." "The superlattices of layer 1-2 and layer 2 are once again 'outof-synch", resulting in a higher-order superlattice that we call'moir-of-mohir superlattice. The system is then cooled to low temperatures (10mK-20K) and studied its electronic transport behavior.

The higher order "moir of moir supralattice" in twisted-trilayergraphene seems to have extremely complex physics both electronically and structurally. The material has the transport signature for superconductivity at a very low electron density (1010 cm-2), which is two orders of magnitude lower than the electron densities reported previously.

Wang stated that "Our experimental results also shed new light on understanding superconductivity" in graphene. "It was believed that electrons must be energetically isolated before they can give birth to superconductivity. However, our experiment suggests otherwise.

The future could see the use of the new material discovered by the team of researchers to fabricate new technology, including quantum electronics and computing platforms. Wang's and his colleagues' findings could be used to inspire other researchers to study the potential for twisted trilayer graphene, or other systems that might lead to a moir of moir’ superlattice.

Wang said that the material they have unveiled could be a promising, atomically-clean supraconductor. It can be electrostatically tuned to extremely low carrier densities change and can be used in future quantum electronic devices. We plan to now study the structural properties and fabrication of gate-defined nanostructures in order to better understand the potential applications.

Continue reading Researchers observe interband collective excitations within twisted bilayer graphene

More information: Correlated superconductivity states and transport signatures of superconductivity within twisted trilayer graphene superlattices. Physical Review Letters (2021).

DOI: 10.1103/PhysRevLett.127.166802 Journal information: Physical Review Letters Correlated insulating states and transport signature of superconductivity in twisted trilayer graphene superlattices. (2021).

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