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2D Ferroelectricity and Bloch lines: The hunt begins

   School of Mathematics and Physics

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  Dr A Kumar, Prof M Gregg  Applications accepted all year round

About the Project

Supervisors : Dr. A Kumar and Prof. JM Gregg

Summary: Research across the globe has recently shown that boundaries between domains (domain walls) in ferroic materials often have unique functional properties that are completely different from the domains that they surround: 2D domain wall (DW) conductors and superconductors can arise in systems where the rest of the material is insulating [1], magnetism can emerge in DWs in non-magnetic crystals [2] and sheets of aligned electrical dipoles can form spontaneously in non-polar materials like CaTiO3 [3]. It has even been suggested that DWs in CaTiO3 and SrTiO3 might actually be 2D ferroelectrics, implying not only the reversibility of polarisation (with applied field), but also the possibility domains WITHIN the DW and hence domain walls within domain walls!! However, establishing comprehensive experimental evidence for such behaviour is a significant challenge and this will be the central focus of this project. We aim to utilise low temperature SPM techniques and other characterisation methods to identify 2D ferroelectricity in these and analogous systems and then fabricate confined structures (e.g. nano-islands) which will allow bias mediated switching of the polarity at these walls. In addition, novel functionalities made accessible by such interfaces will be evaluated for proof-of-concept applications. As opined by Salje and Scott [4,5], vortices inside such polar domain walls in ferroelastic materials can form ordered arrays resembling Bloch-lines in magnets. These Bloch lines are energetically degenerate where the dipoles are oriented perpendicular to the wall. Such walls can have the functionality that they can reverse in polarity even when the polarity of the twin wall may be non-switchable.

Further Details: Amit Kumar, email: [Email Address Removed] ; Prof. Marty Gregg, email: [Email Address Removed]

Funding: This studentship covers fees and a maintenance stipend at current EPSRC rate.

Eligibility: UK and EU nationals who meet residency requirements (https://www.epsrc.ac.uk/skills/students/help/eligibility/)

Entry Requirements: 2:1 (or equivalent) in a cognate physical sciences or engineering discipline.

Application: Applicants should apply electronically through the Queen's online application portal at: https://dap.qub.ac.uk/portal/


Background reading:
[1] J. Seidel et al. Nat. Mater., 8, 229 (2009); E. Y. Ma et al. Science 350, 538 (2015)
[2] S. Farokhipoor et al., Nature 515, 379 (2014);
[3] ‘Direct observation of Ferrielectricity at Ferroelastic Domain Boundaries in CaTiO3 by electron Microscopy’ S. Aert, S. Turner, R. Delville, D. Schryvers, G. Tendeloo and E. Salje, Advanced Materials, 24, 523-527 (2012).
[4] ‘Domain glasses : Twin Planes, Bloch lines, and Bloch Points’ E. Salje and M. Carpenter, Physica Status Solidi B 252, 12, 2639-2648 (2015).
[5] ‘Ferroelectric Bloch-line switching : A paradigm for memory devices ?’ E. Salje and J. Scott, Applied Physics Letters 105, 252904 (2014).
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