arXiv subjects

Rohit S. Nair

Publications and source records attributed to Rohit S. Nair.

3 recordsLinked to original sources

arXiv2021

Spin Hall Effect in a Thin Pt Film

A density-functional-theory based relativistic scattering formalism is used to study charge transport through thin Pt films with room temperature lattice disorder. A Fuchs-Sondheimer specularity coefficient $p \sim 0.5$ is needed to describe the suppression of the charge current at the surface even in the absence of surface roughness. The charge current drives a spin Hall current perpendicular to the surface. Analysing the latter with a model that is universally used to interpret the spin Hall effect in thin films and layered materials, we are unable to recover values of the spin-flip diffusion length $l_{\rm sf}$ and spin Hall angle $Θ_{\rm sH}$ that we obtain for bulk Pt using the same approximations. We trace this to the boundary conditions used and develop a generalized model that takes surface effects into account. A reduced value of $Θ_{\rm sH}$ at the surface is then found to describe the first-principles transport results extremely well. The in-plane spin Hall effect is substantially enhanced at the surface.

cond-mat.mes-hall↗

arXiv2021

Fully resolved currents from quantum transport calculations

We extract local current distributions from interatomic currents calculated using a fully relativistic quantum mechanical scattering formalism by interpolation onto a three-dimensional grid. The method is illustrated with calculations for Pt$|$Ir and Pt$|$Au multilayers as well as for thin films of Pt and Au that include temperature-dependent lattice disorder. The current flow is studied in the "classical" and "Knudsen" limits determined by the sample thickness relative to the mean free path $λ$, introducing current streamlines to visualize the results. For periodic multilayers, our results in the classical limit reveal that transport inside a metal can be described using a single value of resistivity $ρ$ combined with a linear variation of $ρ$ at the interface while the Knudsen limit indicates a strong spatial dependence of $ρ$ inside a metal and an anomalous dip of the current density at the interface which is accentuated in a region where transient shunting persists.

cond-mat.mes-hall↗

arXiv2021

Spin-flip diffusion length in 5d transition metal elements: a first-principles benchmark

Little is known about the spin-flip diffusion length $l_{\rm sf}$, one of the most important material parameters in the field of spintronics. We use a density-functional-theory based scattering approach to determine values of $l_{\rm sf}$ that result from electron-phonon scattering as a function of temperature for all 5d transition metal elements. $l_{\rm sf}$ does not decrease monotonically with the atomic number Z but is found to be inversely proportional to the density of states at the Fermi level. By using the same local current methodology to calculate the spin Hall angle $Θ_{\rm sH}$ that characterizes the efficiency of the spin Hall effect, we show that the products $ρ(T)l_{\rm sf}(T)$ and $Θ_{\rm sH}(T)l_{\rm sf}(T)$ are constant.

cond-mat.mes-hall↗