Deciphering the origin of spin current in spintronic terahertz emitters and its imprint on their electromagnetic radiation via time-dependent density functional theory

Abstract

Spin current flowing between femtosecond laser pulse (fsLP)-driven ferromagnetic metal and adjacent normal metal (NM) hosting strong spin-orbit coupling is invariably invoked to explain terahertz (THz) radiation believed to be emitted solely by NM layer. Despite being such a central concept, the microscopic origin of interlayer spin current remains vague. Here, we employ recently developed [A. Kefayati {\em et al.}, Phys. Rev. Lett. {\bf 133}, 136704 (2024)] time-dependent density functional theory plus Jefimenko equations approach to extract spin current between Co and NM=Pt or NM=W layer where Co is driven by fsLP responsible for its demagnetization, i.e., shrinking of its magnetization vector, $M^y(t)/M^y(t=0)<1$. By comparing time dependence of spin current with those of other relevant quantities, we find that: ({\em i}) spin current is generated by demagnetization dynamics because it {\em follows} closely $d{M}^y/dt$, thus it is an example of quantum pumping phenomenon that cannot be captured by phenomenological notions (such as ``spin voltage'') and related semiclassical transport theories; ({\em ii}) time dependence of pumped spin current {\em does not follow} closely that of charge current emerging within NM layer via spin-to-charge conversion mechanisms; ({\em iii}) THz emission can be governed by {\em both} charge current (i.e., its time derivative entering the Jefimenko equations) within Co layer or NM layer, but in different times frames. We also unravel a special case of NM=W where spin-to-charge conversion by the inverse spin Hall effect and its contribution to THz emission is suppressed, despite large spin Hall angle of W, because of localization of excited electrons onto the outer unfilled $d$-orbitals of W.

arXiv comment9 pages, 3 figures, 90 references

References in corpus (45)

• Nonlocal magnetization dynamics in ferromagnetic heterostructures
• Efficient metallic spintronic emitters of ultrabroadband terahertz radiation
• Scattering approach to parametric pumping
• Super-Diffusive Spin-Transport as a Mechanism of Ultrafast Demagnetization
• An Adiabatic Quantum Electron Pump
• Octopus, a computational framework for exploring light-driven phenomena and quantum dynamics in extended and finite systems
• Spin Transport at Interfaces with Spin-Orbit Coupling: Phenomenology
• Spin Transport at Interfaces with Spin-Orbit Coupling: Formalism
• Thouless pumping and topology
• Time-domain observation of ballistic orbital-angular-momentum currents with giant relaxation length in tungsten
• Attosecond screening dynamics mediated by electron-localization
• Role of Spin Flips versus Spin Transport in Non Thermal Electrons Excited by Ultrashort Optical Pulses in Transition Metals
• Disorder Dependence of Interface Spin Memory Loss
• Spin-memory loss due to spin-orbit coupling at ferromagnet/heavy-metal interfaces: Ab initio spin-density matrix approach
• Spin Hall Effect and Origins of Nonlocal Resistance in Adatom-Decorated Graphene
• Proximity band structure and spin textures on both sides of topological-insulator/ferromagnetic-metal interface and their transport probes
• Transverse spin gradient functional for non-collinear spin density functional theory
• Theory of spin loss at metallic interfaces
• Spin and charge pumping by steady or pulse current-driven magnetic domain wall: A self-consistent multiscale time-dependent-quantum/time-dependent-classical approach
• Particle-in-cell simulation of ultrafast hot-carrier transport in Fe/Au-heterostructures
• Interface reflectivity of a superdiffusive spin current in ultrafast demagnetization and THz emission
• Non-Adiabatic Approximations in Time-Dependent Density Functional Theory: Progress and Prospects
• Spin and charge pumping in magnetic tunnel junctions with precessing magnetization: A nonequilibrium Green function approach
• Spatio-temporal dynamics of shift current quantum pumping by femtosecond light pulse
• Charge pumping by magnetization dynamics in magnetic and semi-magnetic tunnel junctions with interfacial Rashba or bulk extrinsic spin-orbit couplings
• Modeling ultrafast demagnetization and spin transport: the interplay of spin-polarized electrons and thermal magnons
• Spin-to-charge conversion in lateral and vertical topological-insulator/ferromagnet heterostructures with microwave-driven precessing magnetization
• Simulation of Hot-Carrier Dynamics and Terahertz Emission in Laser-Excited Metallic Bilayers
• Probing optical spin-currents using THz spin-waves in noncollinear magnetic bilayers
• Spin-orbit-proximitized ferromagnetic metal by monolayer transition metal dichalcogenide: Atlas of spectral functions, spin textures and spin-orbit torques in Co/MoSe${}_2$, Co/WSe${}_2$ and Co/TaSe${}_2$ heterostructures
• Ultrafast demagnetization in ferromagnetic materials: Origins and progress
• Ab initio investigation of laser-induced ultrafast demagnetization of L1${}_0$ FePt: Intensity dependence and importance of electron coherence
• Theory of AC quantum transport with fully electrodynamic coupling
• Effective spin-mixing conductance of topological-insulator/ferromagnet and heavy-metal/ferromagnet spin-orbit-coupled interfaces: A first-principles Floquet-nonequilibrium-Green-function approach
• Accessing ultrafast spin-transport dynamics in copper using broadband terahertz spectroscopy
• Origins of electromagnetic radiation from spintronic terahertz emitters: A time-dependent density functional theory plus Jefimenko equations approach
• Annihilation of topological solitons in magnetism with spin wave burst finale: The role of nonequilibrium electrons causing nonlocal damping and spin pumping over ultrabroadband frequency range
• Charge and spin current pumping by ultrafast demagnetization dynamics
• Spin transport in an electrically-driven magnon gas near Bose-Einstein condensation: Hartree-Fock-Keldysh theory
• Cooperative Charge Pumping and Enhanced Skyrmion Mobility
• Quantum-classical approach to spin and charge pumping and the ensuing radiation in THz spintronics: Example of ultrafast-light-driven Weyl antiferromagnet Mn${}_3$Sn
• High-harmonic generation in spin and charge current pumping at ferromagnetic or antiferromagnetic resonance in the presence of spin-orbit coupling
• Charge pumping driven by the laser-induced dynamics of the exchange splitting
• Laser-induced charge and spin photocurrents at BiAg${}_2$ surface: a first principles benchmark
• Revealing subterahertz atomic vibrations in quantum paraelectrics by surface-sensitive spintronic terahertz spectroscopy

Cited by in corpus (3)

• Nonclassical dynamics of Néel vector and magnetization accompanied by THz and high-harmonic radiation from ultrafast-light-driven NiO antiferromagnet insulator
• High-efficiency Pt${}_{75}$Au${}_{25}$-based spintronic terahertz emitters
• Optically induced magnetic inertia and magnons from non-Markovian extension of the Landau-Lifshitz-Gilbert equation