arXiv subjects

Jalil Varela Manjarres

Publications and source records attributed to Jalil Varela Manjarres.

2 recordsLinked to original sources

arXiv2023

Comment on "Spin-orbit coupling induced ultrahigh-harmonic generation from magnetic dynamics" with prescriptions on how to validate scientific software for computational quantum transport

In a recent paper [Phys. Rev. B {\bf 105}, L180415 (2022)], Ly and Manchon used open source code {\tt TKWANT} for time-dependent computational quantum transport to predict surprising features in the mature field of current pumping by magnetization dynamics in spintronics -- in the presence of spin-orbit (SO) coupling, the pumped charge current oscillates at both the frequency $ω_0$ of magnetization precession and high harmonics $N=ω/ω_0$, reaching {\em astonishingly high} cutoff \mbox{$N_\mathrm{max} \simeq 1000$} by increasing the SO coupling. However, results in the paper violate two basic theorems of time-dependent quantum transport: ({\em i}) current response to time-periodic external field {\em must be perfectly periodic} itself in the long time limit for a two-terminal device because its active region is attached to two semi-infinite leads bringing continuous energy spectrum; and ({\em ii}) no DC component of charge current is allowed in the left-right symmetric two-terminal devices, or in asymmetric devices its value cannot be changed by simply increasing the SO coupling. We illustrate these two theorems by using completely different calculations applied to one-dimensional two-terminal devices with either ferromagnetic (for which the device is left-right symmetric) and antiferromagnetic (for the device is left-right asymmetric) active region hosting the Rashba SO coupling. We conclude that harmonics in pumped current in the presence of SO coupling do exist, but their ``ultrahigh'' cutoff is an artifact of either ``bugs'' or inadequate algorithms selected within {\tt TKWANT}. Finally, we suggest strategies for {\em validating} time-dependent quantum transport codes, or selection of algorithms by a user within putatively validated (by developers) code, prior to deploying them to produce research papers.

cond-mat.mes-hall↗

arXiv2022

High-harmonic generation in spin and charge current pumping at ferromagnetic or antiferromagnetic resonance in the presence of spin-orbit coupling

One of the cornerstone effects in spintronics is spin pumping by dynamical magnetization that is steadily precessing (around, e.g., the $z$-axis) with frequency $ω_0$, due to absorption of low-power microwaves of frequency $ω_0$ under the resonance conditions and in the absence of any applied bias voltage. The two-decades-old "standard model" of this effect, based on the scattering theory of adiabatic quantum pumping, predicts that component $I^{S_z}$ of spin current vector $\big( I^{S_x}(t),I^{S_y}(t),I^{S_z} \big) \propto ω_0$ is time-independent while $I^{S_x}(t)$ and $I^{S_y}(t)$ oscillate harmonically in time with a single frequency $ω_0$; whereas pumped charge current is zero $I \equiv 0$ in the same adiabatic $\propto ω_0$ limit. Here we employ more general than "standard model" approaches, time-dependent nonequilibrium Green's function (NEGF) and Floquet-NEGF, to predict unforeseen features of spin pumping -- precessing localized magnetic moments within ferromagnetic metal (FM) or antiferromagnetic metal (AFM), whose conduction electrons are exposed to spin-orbit coupling (SOC) of either intrinsic or proximity origin, will pump both spin $I^{S_α}(t)$ and charge $I(t)$ currents. All four of these functions harmonically oscillate in time at both even an odd integer multiples $Nω_0$ of the driving frequency $ω_0$. The cutoff order of such high-harmonics increases with SOC strength, reaching $N_\mathrm{max} \simeq 11$ in the chosen-for-demonstration one-dimensional FM or AFM models. Higher cutoff $N_\mathrm{max} \simeq 25$ can be achieved in realistic two-dimensional (2D) FM models defined on the honeycomb lattice, where we provide prescription on how to realize them using 2D magnets and their heterostructures.

cond-mat.mes-hall↗