Research Area: Epitaxial Topological Semimetals

Topological Semimetals

Semimetals are a category of material that display properties of both metals and non-metals, commonly used in electronics. Topological semimetals are even more unusual, with an electronic structure that leads to states at the surface unseen in any other material. In a Weyl semimetal, a uniquely high flow of charge carriers allows for applications in photonics and electronics. These compounds are also of great interest in particle physics, due to them hosting massless, charged quasiparticles called ‘Weyl fermions’.

Tantalum Arsenide (TaAs) was the first experimentally discovered and most well researched Weyl semimetal. The topological properties and potential applications in quantum computing and advanced electronics lead this material to be of particular interest in thin film and surface science studies.

Tantalum Arsenide body centred tetragonal structure; American Chemical Society

Growth and Analysis of TaAs

TaAs can be grown via Molecular Beam Epitaxy (MBE), where atomically thin layers of material are grown in a vacuum. This growth can be monitored via Rapid High Energy Electron Diffraction (RHEED). This method of analysis relies on reflecting electrons off the material to see the quality and structure of the surface, and can be used to identify the material grown.

Further characterisation of the material grown, including it’s thickness and chemical condition, can be conducted using X-ray Photoemission Spectroscopy (XPS). This uses X-rays to analyse the energy of the electrons present in the material, allowing for the quantification of the amount of substance present at the surface.

Combining these methods allows for the optimisation of TaAs growth, such that a uniform growth recipe can be created.

Strain Relieving Layers

A regular crystal structure represents the ordered nature of the atoms in a solid material. When attempting to grow one material on top of another, it is important to consider how well the crystal structures match each other. If there is a large mismatch, it is challenging to recover a well-ordered surface.

So called ‘strain relieving layers’ seek to reduce large mismatches between materials, by acting as a buffer layer between them. Current research seeks to discover if TaAs has the ability to operate as a strain reliving layer between the semiconductors Indium Antimonide and Gallium Arsenide. It is desirable to have a semimetal strain relieving layer due to it’s unique and robust electronic properties.

Strain caused by lattice mismatch between materials; Journal of Physics, Condensed Matter

Project Aim:

Optimise the growth of the Weyl Semimetal Tantalum Arsenide and investigate it’s capacity to reduce the lattice mismatch between III-V semiconductors Gallium Arsenide and Indium Antimonide.

Freya Slaney-Parker

Previous Study

Physics BSc at the University of Warwick. Final project in Kelvin Probe microscopy optimisation.

Current Study

Scientific Research and Communication MSc at the University of Warwick. Final project in Epitaxial Topological Semimetals.

Contact

Freya.slaney-parker@warwick.ac.uk