Laser-induced terahertz spin transport in magnetic nanostructures arises from the same force as ultrafast demagnetization

Rouzegar, Reza; Brandt, Liane; Nádvorník, Lukáš; Reiss, D. A.; Chekhov, A. L.; Gueckstock, Oliver; In, Chihun; Wolf, Martin; Seifert, Tom S.; Brouwer, Piet W.; Woltersdorf, Georg; Kampfrath, Tobias

doi:10.1103/physrevb.106.144427

Cited by 57 publications

(47 citation statements)

References 99 publications

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“…Both SCC and UDM increase with the pump fluence, indicating that (1) hot electron transport is not hindered by the interface between CoFeB and HM layers, and (2) UDM-based THz emission is proportional to the magnitude of ultrafast demagnetization, before optical damage. All the experimental observations are consistent with the result reported by Rouzegar et al, and strongly demonstrate that SCC and UDM are driven by the same force, the transient spin voltage [ 52 , 53 , 54 ],

, where

and

are the chemical potentials of majority- and minority-spin electrons in the FM layer, respectively.…”

Section: Resultssupporting

confidence: 90%

Terahertz Emission Spectroscopy of Ultrafast Coupled Spin and Charge Dynamics in Nanometer Ferromagnetic Heterostructures

Jiang

Jin

et al. 2022

Nanomaterials

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Due to its high sensitivity and because it does not rely on the magneto-optical response, terahertz (THz) emission spectroscopy has been used as a powerful time-resolved tool for investigating ultrafast demagnetization and spin current dynamics in nanometer-thick ferromagnetic (FM)/heavy metal (HM) heterostructures. Here, by changing the order of the conductive HM coating on the FM nanometer film, the dominant electric dipole contribution to the laser-induced THz radiation can be unraveled from the ultrafast magnetic dipole. Furthermore, to take charge equilibration into account, we separate the femtosecond laser-induced spin-to-charge converted current and the instantaneous discharging current within the illuminated area. The THz emission spectroscopy gives us direct information into the coupled spin and charge dynamics during the first moments of the light–matter interaction. Our results also open up new perspectives to manipulate and optimize the ultrafast charge current for promising high-performance and broadband THz radiation.

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, where

and

are the chemical potentials of majority- and minority-spin electrons in the FM layer, respectively.…”

Section: Resultssupporting

confidence: 90%

Terahertz Emission Spectroscopy of Ultrafast Coupled Spin and Charge Dynamics in Nanometer Ferromagnetic Heterostructures

Jiang

Jin

et al. 2022

Nanomaterials

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“…2. Despite enormous experimental and technological interest in spintronic THz emitters [3][4][5][6][7], as well as fundamental and theoretical interest in far-from-equilibrium [11,12] magnetically ordered quantum materials driven by ultrafast light, very few theoretical approaches have demonstrated complete treatment of phenomena on different time and length scales in these systems, that is, by starting from input fs laser pulse and by proceeding to compute the output THz radiation. For example, we are aware of one such completed treatment [40] where semiclassical transport theory (based on the Boltzmann equation) for incoming laser pulse-driven hot electrons is combined with the Maxwell equations for outgoing EM radiation.…”

Section: Discussionmentioning

confidence: 99%

“…where z max = ea 0 A max / = 0.12 is the dimensionless parameter [21] quantifying maximum amplitude of the pulse; σ = 25 fs is the width of the Gaussian envelope; and center frequency Ω 0 = 2.354 fs −1 is chosen to correspond to 800 nm wavelength commonly employed [3][4][5][6][7][8][9][68][69][70] in THz spintronics.…”

Section: B Spin and Charge Currents Pumped By Light And/or Local Magn...mentioning

confidence: 99%

“…Laser-induced ultrafast demagnetization [1,2] and the ensuing THz spin transport and electromagnetic (EM) radiation-from a single magnetic layer [3] or in contact [3][4][5][6][7][8][9] with an additional layer [Fig. 1] of a nonmagnetic (NM) material but hosting strong spin-orbit coupling (SOC) effects-are central phenomena in femtomagnetism and THz spintronics.…”

Section: Introductionmentioning

confidence: 99%

“…1] of Mn 3 Sn chosen as an illustrative example in this study. Note that time-dependent magnetization of a single FM layer itself emits THz radiation of magnetic-dipole type, but its intensity is orders of magnitude smaller [3] than the signal generated from magnetic bilayers with properly pumped and/or enhanced time-dependent charge current as the radiation source (Sec. II D).…”

Section: Introductionmentioning

confidence: 99%

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Quantum-classical approach to spin and charge pumping and the ensuing radiation in THz spintronics with example of ultrafast-light-driven Weyl antiferromagnet Mn$_3$Sn

Suresh¹,

Nikolić²

2022

Preprint

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The interaction of fs laser pulse with magnetic materials has been intensely studied for more than two decades in order to understand ultrafast demagnetization in single magnetic layers or THz emission from their bilayers with nonmagnetic spin-orbit (SO) materials. However, in contrast to wellunderstood spin and charge pumping by dynamical magnetization in spintronic systems driven by microwaves or current injection, analogous processes in light-driven magnets and radiation emitted by them remain largely unexplained due to multiscale nature of the problem. Here we develop a multiscale quantum-classical formalism-where conduction electrons are described by quantum master equation of the Lindblad type; classical dynamics of local magnetization is described by the Landau-Lifshitz-Gilbert (LLG) equation; and incoming light is described by classical vector potential while outgoing electromagnetic radiation is computed using Jefimenko equations for retarded electric and magnetic fields-and apply it to a bilayer of antiferromagnetic Weyl semimetal Mn3Sn, hosting noncollinear local magnetization, and SO-coupled nonmagnetic material. Our QME+LLG+Jefimenko scheme makes it possible to understand how fs laser pulse generates directly spin and charge pumping and electromagnetic radiation by the latter, including both odd and even high harmonics (of the pulse center frequency) up to order n ≤ 7. The directly pumped spin current then exert spin torque on local magnetization whose dynamics, in turn, pumps additional spin and charge currents radiating in the THz range. By switching on and off LLG dynamics and SO couplings, we unravel which microscopic mechanism contribute the most to emitted THz radiation-charge pumping by local magnetization of Mn3Sn in the presence of its own SO coupling is far more important than standardly assumed (for other types of magnetic layers) spin pumping and subsequent spin-to-charge conversion within the neighboring nonmagnetic SO-coupled material.

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Terahertz Spin‐to‐Charge Current Conversion in Stacks of Ferromagnets and the Transition‐Metal Dichalcogenide NbSe₂

Nádvorník

Gueckstock

Niu

et al. 2022

Adv Materials Inter

Self Cite

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Transition‐metal dichalcogenides (TMDCs) are an aspiring class of materials with unique electronic and optical properties and potential applications in spin‐based electronics. Here, terahertz emission spectroscopy is used to study spin‐to‐charge current conversion (S2C) in the TMDC NbSe2 in ultra‐high‐vacuum‐grown F|NbSe2 thin‐film stacks, where F is a layer of ferromagnetic Fe or Ni. Ultrafast laser excitation triggers an ultrafast spin current that is converted into an in‐plane charge current and, thus, a measurable THz electromagnetic pulse. The THz signal amplitude as a function of the NbSe2 thickness shows that the measured signals are fully consistent with an ultrafast optically driven injection of an in‐plane‐polarized spin current into NbSe2. Modeling of the spin‐current dynamics reveals that a sizable fraction of the total S2C originates from the bulk of NbSe2 with the opposite, negative sign of the spin Hall angle as compared to Pt. By a quantitative comparison of the emitted THz radiation from F|NbSe2 to F|Pt reference samples and the results of ab initio calculations, it is estimated that the spin Hall angle of NbSe2 for an in‐plane polarized spin current lies between ‐0.2% and ‐1.1%, while the THz spin‐current relaxation length is of the order of a few nanometers.

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Laser-induced terahertz spin transport in magnetic nanostructures arises from the same force as ultrafast demagnetization

Cited by 57 publications

References 99 publications

Terahertz Emission Spectroscopy of Ultrafast Coupled Spin and Charge Dynamics in Nanometer Ferromagnetic Heterostructures

Terahertz Emission Spectroscopy of Ultrafast Coupled Spin and Charge Dynamics in Nanometer Ferromagnetic Heterostructures

Quantum-classical approach to spin and charge pumping and the ensuing radiation in THz spintronics with example of ultrafast-light-driven Weyl antiferromagnet Mn$_3$Sn

Terahertz Spin‐to‐Charge Current Conversion in Stacks of Ferromagnets and the Transition‐Metal Dichalcogenide NbSe₂

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Laser-induced terahertz spin transport in magnetic nanostructures arises from the same force as ultrafast demagnetization

Cited by 57 publications

References 99 publications

Terahertz Emission Spectroscopy of Ultrafast Coupled Spin and Charge Dynamics in Nanometer Ferromagnetic Heterostructures

Terahertz Emission Spectroscopy of Ultrafast Coupled Spin and Charge Dynamics in Nanometer Ferromagnetic Heterostructures

Quantum-classical approach to spin and charge pumping and the ensuing radiation in THz spintronics with example of ultrafast-light-driven Weyl antiferromagnet Mn$_3$Sn

Terahertz Spin‐to‐Charge Current Conversion in Stacks of Ferromagnets and the Transition‐Metal Dichalcogenide NbSe2

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Terahertz Spin‐to‐Charge Current Conversion in Stacks of Ferromagnets and the Transition‐Metal Dichalcogenide NbSe₂