On-line SPICE-SPIN+X Seminars
On-line Seminar: 05.03.2025 - 15:00 CET
On the Origin of Electron-Electron Interactions in Bi2Se3 Topological Thin Films
Bryan J Hickey, University of Leeds
We are using Bi2Se3 as a platform in a number of applications in two large collaborative projects: NAME (Nanoscale Advanced Materials Engineering, https://name-pg.uk) and CAMIE ( Combining Advanced Materials with Interface Engineering https://camie.leeds.ac.uk). In our four-chamber deposition system we grow Bi2Se3 by MBE and transfer the samples under UHV to other chambers where we deposit additional layers such as ferromagnets, antiferromagnets, skyrmion bearing multilayers as well as organic layers such as C60. The groundwork for these projects required a growth campaign to obtain material of world class standard and we have characterised our Bi2Se3 using a wide range of techniques. We have achieved excellent epitaxy using a seed layer of (Bi,In)2Se3 and most of the results there are on layers of 20nm Bi2Se3.
Research into the transport properties of Bi2Se3 has been ongoing for many years but there are still questions to be answered about the nature of the conduction in this interesting material. For example, the spin-orbit lifetime is often assumed to be very short but results can be difficult to interpret when the number of conduction channels is reported to be other than 1 or 2, and frequently, it is less than 1. Equally, the spin-orbit scattering should be independent of temperature but it often cannot be seen to be so in many results. Although several papers have suggested that electron-electron interaction effects are observed in, especially the zero-field low-temperature upturn in the resistivity, the nature and origin of these interactions remains unreported.
We have extracted the lifetime of the spin-orbit interaction (!"), by fitting the full expression of the Hikami, Larkin and Nagaoka (HLN) theory for the MR, which is indeed short in the best materials ~ 10-14 s but can be longer in others. We show that fits to the MR can be achieved with a temperature independent value of !". In the strong spin-orbit limit, the approximate HLN function applies and then the fits return only a single conduction channel. The full analysis allows us to extract the electron-electron interaction time (## )
as a function of temperature and hence determine its origin in terms of Fermi liquid theory
and the effects of a finite mean free path, i.e. ($ ℓ).
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