One of the cornerstone effects in spintronics is spin pumping by dynamical magnetization that is steadily precessing (around, for example, the
The Coulombfree^{1}
 Award ID(s):
 1927130
 NSFPAR ID:
 10414362
 Publisher / Repository:
 Nature Publishing Group
 Date Published:
 Journal Name:
 Communications Physics
 Volume:
 6
 Issue:
 1
 ISSN:
 23993650
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
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Abstract z axis) with frequencyω _{0}due to absorption of lowpower microwaves of frequencyω _{0}under the resonance conditions and in the absence of any applied bias voltage. The twodecadesold ‘standard model’ of this effect, based on the scattering theory of adiabatic quantum pumping, predicts that component of spin current vector ${I}^{{S}_{z}}$ is timeindependent while $({I}^{{S}_{x}}(t),{I}^{{S}_{y}}(t),{I}^{{S}_{z}})\propto {\omega}_{0}$ and ${I}^{{S}_{x}}(t)$ oscillate harmonically in time with a single frequency ${I}^{{S}_{y}}(t)$ω _{0}whereas pumped charge current is zero in the same adiabatic $I\equiv 0$ limit. Here we employ more general approaches than the ‘standard model’, namely the timedependent nonequilibrium Green’s function (NEGF) and the Floquet NEGF, to predict unforeseen features of spin pumping: namely precessing localized magnetic moments within a 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 $\propto {\omega}_{0}$ and charge ${I}^{{S}_{\alpha}}(t)$I (t ) currents. All four of these functions harmonically oscillate in time at both even and odd integer multiples of the driving frequency $N{\omega}_{0}$ω _{0}. The cutoff order of such high harmonics increases with SOC strength, reaching in the onedimensional FM or AFM models chosen for demonstration. A higher cutoff ${N}_{\mathrm{m}\mathrm{a}\mathrm{x}}\simeq 11$ can be achieved in realistic twodimensional (2D) FM models defined on a honeycomb lattice, and we provide a prescription of how to realize them using 2D magnets and their heterostructures. ${N}_{\mathrm{m}\mathrm{a}\mathrm{x}}\simeq 25$ 
Abstract We present
H band interferometric observations of the red supergiant (RSG) AZ Cyg that were made with the Michigan InfraRed Combiner (MIRC) at the sixtelescope Center for High Angular Resolution Astronomy (CHARA) Array. The observations span 5 yr (2011–2016), which offers insight into the short and longterm evolution of surface features on RSGs. Using a spectrum of AZ Cyg obtained with SpeX on the NASA InfraRed Telescope Facility (IRTF) and synthetic spectra calculated from spherical MARCS, spherical PHOENIX, and SAtlas model atmospheres, we deriveT _{eff}is between 3972 K and 4000 K and between −0.50 and 0.00, depending on the stellar model used. Using fits to the squared visibility and GAIA parallaxes, we measure its average radius $\mathrm{log}\phantom{\rule{0.25em}{0ex}}g$ . Reconstructions of the stellar surface using our modelindependent imaging codes SQUEEZE and OITOOLS.jl show a complex surface with small bright features that appear to vary on a timescale of less than one year and larger features that persist for more than one year. The 1D power spectra of these images suggest a characteristic size of 0.52–0.69 $R={911}_{50}^{+57}\phantom{\rule{0.25em}{0ex}}{R}_{\odot}$R _{⋆}for the larger, long lived features. This is close to the values of 0.51–0.53R _{⋆}that are derived from 3D RHD models of stellar surfaces. We conclude that interferometric imaging of this star is in line with predictions of 3D RHD models but that shortterm imaging is needed to more stringently test predictions of convection in RSGs. 
Abstract The repeating fast radio burst FRB 20190520B is localized to a galaxy at
z = 0.241, much closer than expected given its dispersion measure DM = 1205 ± 4 pc cm^{−3}. Here we assess implications of the large DM and scattering observed from FRB 20190520B for the host galaxy’s plasma properties. A sample of 75 bursts detected with the Fivehundredmeter Aperture Spherical radio Telescope shows scattering on two scales: a mean temporal delayτ (1.41 GHz) = 10.9 ± 1.5 ms, which is attributed to the host galaxy, and a mean scintillation bandwidth Δν _{d}(1.41 GHz) = 0.21 ± 0.01 MHz, which is attributed to the Milky Way. Balmer line measurements for the host imply an Hα emission measure (galaxy frame) EM_{s}= 620 pc cm^{−6}× (T /10^{4}K)^{0.9}, implying DM_{Hα}of order the value inferred from the FRB DM budget, pc cm^{−3}for plasma temperatures greater than the typical value 10^{4}K. Combining ${\mathrm{DM}}_{\mathrm{h}}={1121}_{138}^{+89}$τ and DM_{h}yields a nominal constraint on the scattering amplification from the host galaxy , where $\tilde{F}G\phantom{\rule{0.50em}{0ex}}=\phantom{\rule{0.50em}{0ex}}{1.5}_{0.3}^{+0.8}{({\mathrm{pc}}^{2}\phantom{\rule{0.25em}{0ex}}\mathrm{km})}^{1/3}$ describes turbulent density fluctuations and $\tilde{F}$G represents the geometric leverage to scattering that depends on the location of the scattering material. For a twoscreen scattering geometry whereτ arises from the host galaxy and Δν _{d}from the Milky Way, the implied distance between the FRB source and dominant scattering material is ≲100 pc. The host galaxy scattering and DM contributions support a novel technique for estimating FRB redshifts using theτ –DM relation, and are consistent with previous findings that scattering of localized FRBs is largely dominated by plasma within host galaxies and the Milky Way. 
Abstract The repeating fast radio burst FRB 20190520B is an anomaly of the FRB population thanks to its high dispersion measure (DM = 1205 pc cm^{−3}) despite its low redshift of
z _{frb}= 0.241. This excess has been attributed to a large host contribution of DM_{host}≈ 900 pc cm^{−3}, far larger than any other known FRB. In this paper, we describe spectroscopic observations of the FRB 20190520B field obtained as part of the FLIMFLAM survey, which yielded 701 galaxy redshifts in the field. We find multiple foreground galaxy groups and clusters, for which we then estimated halo masses by comparing their richness with numerical simulations. We discover two separateM _{halo}> 10^{14}M _{⊙}galaxy clusters atz = 0.1867 and 0.2170 that are directly intersected by the FRB sight line within their characteristic halo radiusr _{200}. Subtracting off their estimated DM contributions, as well that of the diffuse intergalactic medium, we estimate a host contribution of or ${\mathrm{D}\mathrm{M}}_{\mathrm{h}\mathrm{o}\mathrm{s}\mathrm{t}}={430}_{220}^{+140}$ (observed frame), depending on whether we assume that the halo gas extends to ${280}_{170}^{+140}\phantom{\rule{0.25em}{0ex}}\mathrm{p}\mathrm{c}\phantom{\rule{0.25em}{0ex}}{\mathrm{c}\mathrm{m}}^{3}$r _{200}or 2 ×r _{200}. This significantly smaller DM_{host}—no longer the largest known value—is now consistent with Hα emission measures of the host galaxy without invoking unusually high gas temperatures. Combined with the observed FRB scattering timescale, we estimate the turbulent fluctuation and geometric amplification factor of the scattering layer to be , suggesting that most of the gas is close to the FRB host. This result illustrates the importance of incorporating foreground data for FRB analyses both for understanding the nature of FRBs and to realize their potential as a cosmological probe. $\tilde{F}G\approx 4.5\u201311{({\mathrm{pc}}^{2}\phantom{\rule{0.25em}{0ex}}\mathrm{km})}^{1/3}$ 
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