Emergent electronic phenomena due to twist degree of freedom in van der Waals heterostructures

Van der Waals heterostructures [1] are stacks of atomically thin materials (called two-dimensional atomic crystals) like graphene, hexagonal boron nitride or transition metal dichalcogenides. In contrast to conventional heterostructures, in which chemical bonding of constituent elements both modifies their properties and requires lattice matching for stability of defect-less structures, van der Waals heterostructures are glued by weak forces that do not lead to directional bonding. As a result, any two two-dimensional crystals can be placed on top of each other, allowing for unprecedented freedom in selection of components and design of new artificial materials. Moreover, two crystals can be stacked at any relative angle between their crystallographic axes and changing it can drastically modify the properties of the heterostructure, with small rotations making the difference between, for example, making the structure superconducting or not, as recently shown in the case of so called “magic-angle” twisted bilayer graphene [2,3].

From the theoretical point of view, studying the properties of stacks of misaligned atomic crystals presents some difficulties: for an arbitrary angle, the interface is incommensurate and Bloch’s theorem, the cornerstone of solid state physics, is seemingly not applicable, invalidating all standard approaches to modelling properties of crystals. Even for angles leading to commensurate ‘superstructures’, brute force computational approaches struggle because of the huge number of atoms in a unit cell so that a novel approach is necessary.

In this project, you will investigate theoretically new phenomena which emerge in van der Waals heterostructures due to the interaction between two crystals and are driven by changes in the atomistic geometry at the interface between van der Waals-coupled materials. You will develop effective models to describe electronic, optical and vibrational properties of such heterostructures at any angle and use both analytical and computational tools to search for and study situations in which many-body effects lead to novel behaviour.

The project will be realised within the group led by Dr Marcin Mucha-Kruczynski in potential collaboration with other theoretical or experimental groups in the UK or abroad. For more detailed information on the research and the group, please visit http://people.bath.ac.uk/mlmk20/

Candidate -

The successful candidate should hold, or expect to receive, a first class or good 2.1 Master’s degree (or equivalent) in Physics (Theoretical Physics preferred) or Theoretical/Quantum Chemistry (or other closely related field). A keen interest in theoretical condensed matter physics and a strong work ethic are essential. Also required is basic programming experience (knowledge of Matlab/Mathematica will be beneficial but is not necessary).

Applications -

Informal enquiries are welcomed and should be directed to Dr Marcin Mucha-Kruczynski, [Email Address Removed].

Formal applications should be made via the University of Bath’s online application form for a PhD in Physics:
https://samis.bath.ac.uk/urd/sits.urd/run/siw_ipp_lgn.login?process=siw_ipp_app&code1=RDUPH-FP01&code2=0013

More information about applying for a PhD at Bath may be found here:
http://www.bath.ac.uk/guides/how-to-apply-for-doctoral-study/

Anticipated start date: 30 September 2019