In this project we aim to measure fundamental properties of 2D materials. 2D materials are amazing materials which are only 1 or a few atomic layer thick, but, which can be up to several square-centimeters or even square-meters large. 2D materials are very important for the development of new electronics, for example so called flexible electronics which can be incorporated in the body, clothing etc. It was recently shown that two layers of the 2D material graphene (graphene is a monolayer of carbon) can become superconducting when the two layers are placed in a twisted fashion on top of each other - magic angle graphene. Superconducting is great, because it enables electricity to be conducted without heat loss, but at present it is not well understood how this magic angle graphene superconductivity comes about.
In this project we will use a beam of neutral helium atoms to investigate how flexible the 2D layers really are and how this flexiblity changes with temperature and we will measure how the vibrations of the atoms in the material affect how the electrons in the materials move, which should enable us to understand what type of superconductivity these materials show.
2D materials have been extensively researched since the discovery of graphene in 2004. Some 2D materials have attracted particular interest in recent years for two reasons: they can exhibit superconductivity and/or they can be used in flexible electronics. The 2018 «Physics World Breakthrough of the year» showed that when two graphene layers are rotated 1.1° the material becomes superconducting. This year superconductivity was also found in two twisted trilayer graphene systems and sample provider for this project Prof. Stevan Nadj-Perge, Caltech, showed that the superconducting properties of maging angle graphene improves when it is placed on a different substrate. The nature of superconductivity in these 2D materials is not well understood. This hampers the design of new superconducting 2D materials.
Flexible electronics is pursued intensively for applications such as foldable displays, wearable biosensors, implants for monitoring life signs, artificial nerves, muscle implants and soft robotics. However, to design flexible electronic components that do not fracture when bent, it is important to know how flexible the different material layers are relative to each other (bending rigidity). For the components to work over a sufficiently large temperature range, it is important to know how the bending rigidity changes with temperature. At present there are no experimental measurements on this for 2D materials and the different theories disagree.
In this project, we use helium scattering to measure i) the electron-phonon coupling in the low frequency range believed to be particular important for superconductivity of 2D materials, due to the recently observed substrate influence, and ii) temperature-dependent bending rigidity for a range of 2D materials. These properties cannot be measured directly with any other technique. The project will provide crucial information on how to design future 2D superconductors and flexible electronics components.