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Superconducting Spintronics in van der Waals Heterostructures


   Department of Physics

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  Prof Simon Bending, Prof Daniel Wolverson  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.

Overview of the Project: 

The Holy Grail of electronic device development is a structure that combines the functionalities of superconductivity and spintronics; the former allows the dissipationless transport of electrical currents while the latter is at the heart of fast, energy-efficient modern devices whose operation is controlled by the flow of spin currents. Together these open up a vast range of new applications for spin transport in electronic logic circuits and memory cells in which Joule heating and dissipation would be minimal. Ferromagnetism and superconductivity are generally incompatible phenomena since the exchange field which aligns electron spins in the former leads to the destruction of the opposite-spin Cooper pairs normally responsible for superconductivity. However, it was recently demonstrated both theoretically [1] and experimentally [2-4] that spin triplet electron pair correlations can arise at the interface between a superconductor and a ferromagnet and can carry supercurrents over very much longer distances in strong ferromagnets than conventional spin singlet pairs.

 Previous work has relied on multilayer structures produced by physical vapour deposition with relatively rough and poorly characterised interfaces. We have recently exploited breakthroughs in ‘dry stamping’ of twisted van der Waals heterostructures [5] to demonstrate high quality Josephson junctions and Superconducting QUantum Interferometer Devices (SQUIDs) [6]. We will build on this work to realise superspintronic structures with well-controlled, atomically sharp interfaces. Various functional 2D materials are now available to realise such structures including NbSe2 or Bi2Sr2CaCu2O8+d as the superconducting electrodes and Fe3GeTe2, Cr2Ge2Te6, CrBr3, CrI3 or CrCl3 as the ferromagnetic ‘barrier’ layers. Long range triplet generation requires rotation of the spin quantisation axis for scattered electron pairs near the barrier interface and this can readily be achieved by including additional ferromagnetic layers with different magnetisation directions or non-magnetic layers with strong spin-orbit coupling [7].

This is an interdisciplinary project combining materials science, device fabrication and quantum transport. The PhD will develop in two main areas:-

Device preparation: You will use the advanced tools in the Nanofabrication Facility to produce substrates with pre-patterned contacts for subsequent device assembly. You will then use the dry transfer setup we have developed in a nitrogen glovebox to produce precisely controlled vdW heterostructures with high quality interfaces.

Quantum transport. You will perform low temperature transport measurements in our cryocooler-based systems on heterostructures with various ferromagnetic barrier layers in order to distinguish the role played by singlet and triplet correlations and optimise the conditions for the generation of spin-triplet supercurrents. Once this is understood, active devices will be explored in which the magnetic configuration can be switched by an applied magnetic field or transport current.

The project will be supervised by Prof Simon Bending and Prof Daniel Wolverson at the University of Bath. Our laboratories are part of the Centre for Nanoscience and Nanotechnology (CNAN) and include an advanced glovebox-based heterostructure stamping rig. We also have access to state-of-the-art University nanofabrication (David Bullett Labs) and characterisation (Materials and Chemical Characterisation Labs) facilities.

Project keywords: Van der Waals heterostructures; Two-dimensional materials; Superconductivity; Spintronics; Josephson junctions.

Candidate Requirements:

Applicants should hold, or expect to receive, a First Class or good Upper Second Class Honours degree (or the equivalent) in Physics, Electrical Engineering or Physical Chemistry. A master’s level qualification would also be advantageous. An aptitude for experimental physics is required and the project could also involve opportunities to become involved in the development of supporting theory.

Non-UK applicants must meet our English language entry requirement.

Enquiries and Applications:

Informal enquiries are welcomed and should be directed to Prof Simon Bending (email: [Email Address Removed]).

Formal applications should be made via the University of Bath’s online application form for a PhD in Physics.

More information about applying for a PhD at Bath may be found on our website.

Equality, Diversity and Inclusion:

We value a diverse research environment and aim to be an inclusive university, where difference is celebrated and respected. We welcome and encourage applications from under-represented groups.

If you have circumstances that you feel we should be aware of that have affected your educational attainment, then please feel free to tell us about it in your application form. The best way to do this is a short paragraph at the end of your personal statement.


Funding Notes

Self-funded students only.

References

[1] Houzet & Buzdin, PRB 76, 060504(R) (2007); Eschrig & Löfwander, Nat Phys 4. 138 (2008).
[2] Robinson et al., Science 329, 59 (2010)..
[3] Khaire et al., PRL 104, 137002 (2010).
[4] Flokstra et al., Nat. Phys. 12, 57 (2016)].
[5] Geim & Grigorieva, Nature 499, 419 (2013).
[6] Farrar et al., Nano Lett. 21, 6721 (2021).
[7] Bergeret & Tokatly, PRB 89, 134517 (2014).

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