Attosecond magnetization dynamics in non-magnetic materials driven by intense femtosecond lasers

Irradiating solids with ultrashort laser pulses is known to initiate femtosecond timescale magnetization dynamics.However,sub-femtosecond spin dynamics have not yet been observed or predicted.Here,we explore ultrafast light-driven spin dynamics in a highly nonresonant strong-field regime.Through state-of-the-art ab initio calculations,we predict that a nonmagnetic material can transiently transform into a magnetic one via dynamical extremely nonlinear spin-flipping processes,which occur on attosecond timescales and are mediated by cascaded multi-photon and spin–orbit interactions.These are nonperturbative nonresonant analogs to the inverse Faraday effect,allowing the magnetization to evolve in very high harmonics of the laser frequency(e.g.here up to the 42nd,oscillating at~100 attoseconds),and providing control over the speed of magnetization by tuning the laser power and wavelength.Remarkably,we show that even for linearly polarized driving,where one does not intuitively expect the onset of an induced magnetization,the magnetization transiently oscillates as the system interacts with light.This response is enabled by transverse light-driven currents in the solid,and typically occurs on timescales of~500 attoseconds(with the slower femtosecond response suppressed).An experimental setup capable of measuring these dynamics through pump–probe transient absorption spectroscopy is simulated.Our results pave the way for attosecond regimes of manipulation of magnetism.

进行中的弗洛凯能带工程

In a recent article in Nature,Zhou et al.[1]reported an impressive demonstration of Floquet materials engineering.In this field researchers aim at creating properties in materials that they do not usually exhibit in their equilibrium state.The scope ranges from inducing phase transitions in out-of-equilibrium that can otherwise only be achieved by pressure or doping.

Effect of spin-orbit coupling on the high harmonics from the topological Dirac semimetal Na3Bi

In this work,we performed extensive first-principles simulations of high-harmonic generation in the topological Diract semimetal Na_(3)Bi using a first-principles time-dependent density functional theory framework,focusing on the effect of spin-orbit coupling(SOC)on the harmonic response.We also derived an analytical model describing the microscopic mechanism of strong-field dynamics in presence of spin-orbit coupling,starting from a locally U(1)×SU(2)gauge-invariant Hamiltonian.Our results reveal that SOC:(i)affects the strong-field excitation of carriers to the conduction bands by modifying the bandstructure of Na_(3)Bi,(ii)makes each spin channel reacts differently to the driven laser by modifying the electron velocity(iii)changes the emission timing of the emitted harmonics.Moreover,we show that the SOC affects the harmonic emission by directly coupling the charge current to the spin currents,paving the way to the high-harmonic spectroscopy of spin currents in solids.

Microscopic theory of light-induced ultrafast skyrmion excitation in transition metal films

Magnetic skyrmions are topological excitations of great promise for compact and efficient memory storage.However,to interface skyrmionics with electronic devices requires efficient and reliable ways of creating and destroying such excitations.In this work,we unravel the microscopic mechanism behind ultrafast skyrmion generation by femtosecond laser pulses in transition metal thin films.We employ a theoretical approach based on a two-band electronic model,and show that by exciting the itinerant electronic subsystem with a femtosecond laser ultrafast skyrmion nucleation can occur on a 100 fs timescale.By combining numerical simulations with an analytical treatment of the strong s–d exchange limit,we identify the coupling between electronic currents and the localized d-orbital spins,mediated via Rashba spin–orbit interactions among the itinerant electrons,as the microscopic and central mechanism leading to ultrafast skyrmion generation.Our results show that an explicit treatment of itinerant electron dynamics is crucial to understand optical skyrmion generation.

Dynamical amplification of electric polarization through nonlinear phononics in 2D SnTe

Ultrafast optical control of ferroelectricity using intense terahertz fields has attracted significant interest.Here we show that the nonlinear interactions between two optical phonons in SnTe,a two-dimensional in-plane ferroelectric material,enables a dynamical amplification of the electric polarization within subpicoseconds time domain.Our first-principles time-dependent simulations show that the infrared-active out-of-plane phonon mode,pumped to nonlinear regimes,spontaneously generates in-plane motions,leading to rectified oscillations in the in-plane electric polarization.We suggest that this dynamical control of ferroelectric material,by nonlinear phonon excitation,can be utilized to achieve ultrafast control of the photovoltaic or other nonlinear optical responses.