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Exposing the nanoscale ultrafast dynamics of Dirac systems via near-field terahertz spectroscopy

  • Full or part time
  • Application Deadline
    Applications accepted all year round
  • Funded PhD Project (European/UK Students Only)
    Funded PhD Project (European/UK Students Only)

Project Description

To create energy-efficient, faster ’21st century devices’ that can impact a range of sectors, including healthcare, wireless communication, defence, security and clean energy, integrated photonic, electronic and quantum technologies are essential. Advanced functional materials, including graphene, 2D materials and III-V nanowires, have emerged as potential building blocks for these technologies. Dirac materials, in particular, have attracted significant attention, owing to the intrinsic high electron mobility and doping tunability provided by their linear dispersion relation. Dirac semi-metals form a 3D analogue of graphene. Whereas topological insulators are insulating in the bulk, yet possess perfectly conducting surface states. For both materials, the surface hosts Dirac electrons that travel close to the speed of light and are immune to backscattering from non-magnetic impurities and defects. Their direction of travel is fixed by their inherent angular momentum or ’spin’, so they behave as if on a railway line - travelling with less resistance and heat production.
To date, it is has been difficult to isolate this surface response and harness these ultrafast spin-polarised surface currents within a devices. The bulk carrier density often dominates the conductivity response. Surface-sensitive techniques are therefore essential for gaining an understanding of the fundamental physics behind this exotic surface state. Terahertz spectroscopy has already been proven as a powerful non-contact tool for measuring the electrical conductivity of a material. By looking at the THz radiation transmitted/reflected through/from a sample, key optoelectronic properties, such as electron mobility and carrier concentration, can be extracted in a non-contact fashion. However, the spatial resolution is limited to the micron scale by the diffraction limit of light. This project will combine scanning near-field optical microscopy with terahertz spectroscopy to push the spatial resolution of this technique down to the nanoscale. It will provide a unique tool for extracting the optoelectronic properties of Dirac materials with nanometre (<30nm) spatial resolution. The local ultrafast carrier dynamics of topological insulator and Dirac semi-metal thin films and nanostructures will be extracted, providing novel insight into the underlying physical mechanisms governing these exciting materials.
To achieve the key aims for this project, the student will be expected to:
• Conduct far-field terahertz spectroscopy on topological insulator and/or Dirac semi-metal thin films and nanostructures and study their microscale optoelectronic properties.
• Assist with development of near-field terahertz microscope system and optimise its performance.
• Perform near-field terahertz microscopy on topological insulator and/or Dirac semi-metal thin films and nanostructures and study their nanoscale optoelectronic properties.
• Supplement terahertz experiments with other optical techniques, eg. Raman, PL, to provide further understanding of the nanoscale optoelectronic properties of these materials.
This project will suit a candidate with some experience in one or more of terahertz, optics, nanotechnology, ultrafast lasers, ultrafast spectroscopy, microscopy techniques, Dirac and/or topological physics.

Funding Notes

The post is supported by a bursary and fees (at the UK/EU student rate) provided by the EPSRC.

The award is only open to UK and certain EU applicants only. Please check your suitability at the following web site:
View Website.

References

We are seeking an enthusiastic and self-motivated person who meets the academic requirements for enrolment for a doctorate at the University of Manchester. You will ideally have a 1st class, but at least a UK upper 2nd class, honours degree (or equivalent) in electrical engineering or a related subject.

How to apply: Interested applicants should send an up-to-date CV to Ms Marie Davies at [email protected] with a covering letter explaining their interest and suitability for this research.

Related Subjects

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