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Quantum memory effects in charge density wave transition metal chalcogenides


Department of Physics

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Dr Enrico Da Como , Prof Simon Bending Applications accepted all year round Self-Funded PhD Students Only

About the Project

The University of Bath is inviting applications for the following PhD project supervised by Dr Enrico Da Como (https://people.bath.ac.uk/edc25/) and Prof Simon Bending (https://researchportal.bath.ac.uk/en/persons/simon-bending) in the Department of Physics.

Living in the age of information technology and data storage there is an imminent need for new solid state materials capable of storing information and/or performing computational tasks by writing and erasing information in the form of quantum states. In the search for materials with applications in new disruptive technologies, two-dimensional (2D) transition metal dichalcogenides (TMDs) are in a dominant position, because of their unique electronic band structure, the easy interfacing with device architectures and graphene-based platforms, combined with chemical versatility.

In particular metallic TMDs are known to exhibit a plethora of electronic phases where strong electron interactions drive ordered phases such as charge density wave (CDW) instabilities, superconducting charge pairing, topologically induced gaps and Mott metal-insulator states. The research in our group has so far been focussed on the fundamentals of these electronic ordered states and the possibility to control them using laser light [1] or electric fields in field-effect structures [2].

In this project we aim at exploring and understanding the CDW dynamics in the Tantalum based TMDs: TaS2, TaSe2 and the mixed compound TaSxSe1-x. The motivation comes from recent preliminary data from our laboratory showing that at defined stoichiometries the mixed compound has a unique hysteric behaviour in the electric resistivity as a function of temperature. While this holds promise for real applications in memories, it also opens a number of interesting questions on the energetic landscape of the CDW configurations in this material. By definition CDW are macroscopic quantum states where electrons group into waves with the same periodicity of the lattice, which is distorted with respect to its original above the transition structure. For tantalum based compounds it is the degree of commensurability that sometimes defines new CDW states and possibly and energy landscape with shallow minima.

The objectives of the research program consist in 1) design of mixed compounds TaSxSe1-x with optimal quantum memory effects, 2) investigation of electron dynamics by means of quantum transport measurements: resistivity, Hall effect, AC capacitance, 3) study of the electronic structure with optical and photoemission techniques (ARPES) and investigation of incommensurability, 4) demonstration of write/erase control using temperature, electric fields or laser light on prototype memory devices.

This PhD project will offer you the opportunity to learn about spectroscopic methods aiming at understanding the electronic structure, combined with studies on electronic devices and theoretical models of band structure. You will join the University of Bath physics department where a strong research focus on TMDs has been established. The supervisory team has expertise in the different areas and is already collaborating on these materials through the Centre for Doctoral Training in Condensed Matter Physics [3]. The proposed experience for PhD students is thus covering the research fields of quantum electronic transport at low temperatures and spectroscopy of quantum materials.

Candidate requirements:

Applicants should hold, or expect to receive, a First Class or good Upper Second Class Honours degree, or the equivalent from an overseas university. A master’s level qualification would also be advantageous.

Enquiries and applications:

Informal enquiries are welcomed and should be directed to Dr Enrico Da Como on email address [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=0014

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/

Funding Notes

We welcome all-year-round applications from self-funded candidates and candidates who can source their own funding.

References

[1] H. Hedayat, C. J. Sayers, D. Bugini, C. Dallera, D. Wolverson, T. Batten, S. Karbassi, S. Friedemann, G. Cerullo, J. van Wezel, S. R. Clark, E. Carpene, and E. Da Como, Physical Review Research, 1, 023029, (2019)
[2] L. Farrar, M. Bristow, A. A. Haghighirad, A. McCollam, S. J. Bending, A. I. Coldea arXiv:1907.13174 (2019)
[3] C. J. Sayers, L. S. Farrar, S. J. Bending, M. Cattelan, A. J. H. Jones, N. A. Fox, G. Kociok-Kohn, K. Koshmak, J. Laverock, L. Pasquali, and E. Da Como, under review (2019)
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