O.M. Stewart Colloquium Series

Monday, March 20, 2017 4:00pm

120 Physics Building

Departments: 

Prof. Paul J. Kelly, Faculty of Science and Technology and MESA+ Institute for Nanotechnology, University of Twente, The Netherlands presents, "Turning up the Heat in First Principles Quantum Spin Transport," Monday, march 20 at 4:00 p.m. in Room 120, Physics Building. Refreshments will be served at 3:30pm in room 223A.

Prof. Paul J. Kelly

The spin Hall angle (SHA) is a measure of the efficiency with which a transverse spin current is generated from a charge current by the spin-orbit coupling and disorder in the spin Hall effect (SHE). In a study of the SHE for a Pt|Py (Py=Ni80Fe20) bilayer using a first-principles scattering approach, we find a SHA that increases monotonically with temperature and is proportional to the resistivity for bulk Pt. By decomposing the room temperature SHE and inverse SHE currents into bulk and interface terms, we discover a giant interface SHA that dominates the total inverse SHE current with potentially major consequences for applications.

To study bulk Pt, we set up a scattering geometry consisting of two crystalline semi-infinite Pt leads sandwiching a scattering region of length LPt of disordered Pt with atoms displaced from their equilibrium positions by populating phonon modes. For the resistivity and spin-flip diffusion length, this approach has been shown to yield essentially perfect agreement with experiment. We study the SHE by calculating local longitudinal and transverse charge and spin current densities in the scattering region so that both intrinsic and extrinsic contributions are naturally included. To study interface effects, we model a Py|Pt bilayer by matching 9x9 interface unit cells of Py to 37x37 unit cells of Pt including both lattice and spin disorder in Py. Fig.1b shows the results obtained for bulk Pt at room temperature. This presentation will introduce and review the computational procedures that make these calculations possible.