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Lessons learned from topology to maximize the spin Hall effect

Lessons learned from topology to maximize the spin Hall effect
date:

Dienstag, 28.11.2017, 15.45 Uhr

place:

Seminarraum 3-1, Physikhochhaus

speaker:

Dr. Mazhar Ali
Max-Planck-Institut für Mikrostrukturphysik Halle

Abstract: Recent years have seen a dramatic change in the understanding of electronic structures
and some electronic properties, stemming from the rise of topological physics. In particular,  topological insulators, massless Dirac, Weyl and Nodal Line semimetals have all been discovered and manifested in solid state systems. We briefly introduce these concepts and the field before  continuing on to the application of lessons learned from topology to contemporary technologies, focusing on spintronics. The spin Hall effect effect  (SHE) is the conversion of a charge current to a spin current and non-magnetic magnetic metals with a large SHE are useful for a variety of spintronic applications, but their rarity has stifled their widespread use. We predict the presence of a large intrinsic SHE in the A15 family of superconductors: Ta 3 Sb, Nb 3 Au, and Cr 3 Ir having spin hall conductivities of -1400, -1060, and 1210 hbar/e Ohm/cm, respectively. By combining concepts from topological physics with the dependence of the SHE on the Berry Curvature Curvature
 of the electronic structure, we propose a simple strategy to design materials with a large intrinsic SHE based on the following ideas: that high symmetry combined with heavy atoms can give rise to multiple Dirac or Weyl crossings in the electronic structure, that these crossings can gap due to spin orbit coupling without sufficient symmetry  protection, and that gapped Dirac crossings can create a large Berry Curvature. We use these to explain why beta-W and Pt have a large intrinsic SHE and present a family of sputterable, large SHE  compounds and alloys (e.g. W 3 Ta, 2250). With
tuning of extrinsic parameters, this approach will represent a new direction in the route to efficient
charge/spin conversion.