Controlling the magnetic state of the proximate quantum spin liquid α-RuCl_(3) with an optical cavity

Harnessing the enhanced light-matter coupling and quantum vacuum fluctuations resulting from mode volume compression in optical cavities is a promising route towards functionalizing quantum materials and realizing exotic states of matter.Here,we extend cavity quantum electrodynamical materials engineering to correlated magnetic systems,by demonstrating that a Fabry-Pérot cavity can be used to control the magnetic state of the proximate quantum spin liquidα-RuCl_(3).Depending on specific cavity properties such as the mode frequency,photon occupation,and strength of the light-matter coupling,any of the magnetic phases supported by the extended Kitaev model can be stabilized.In particular,in the THz regime,we show that the cavity vacuum fluctuations alone are sufficient to bringα-RuCl_(3) from a zigzag antiferromagnetic to a ferromagnetic state.By external pumping of the cavity in the few photon limit,it is further possible to push the system into the antiferromagnetic Kitaev quantum spin liquid state.

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.

From basic properties to the Mott design of correlated delafossites

The natural-heterostructure concept realized in delafossites highlights these layered oxides.While metallic,band-or Mott-insulating character may be associated with individual layers,inter-layer coupling still plays a decisive role.We review the correlated electronic structure of PdCoO_(2),PdCrO_(2),and AgCrO_(2),showing that layer-entangled electronic states can deviate from standard classifications of interacting systems.This finding opens up possibilities for materials design in a subtle Mott-critical regime.Manipulated Hidden-Mott physics,correlation-induced semimetallicity,or Dirac/flat-band dispersions in a Mott background are emerging features.Together with achievements in the experimental preparation,this inaugurates an exciting research field in the arena of correlated materials.

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.

Common microscopic origin of the phase transitions in Ta_(2)NiS_(5) and the excitonic insulator candidate Ta_(2)NiSe_(5)

The structural phase transition in Ta-NiSes has been envisioned as driven by the formation of an excitonic insulating phase.However,the role of structural and electronic instabilities on crystal symmetry breaking has yet to be disentangled.Meanwhile,the phase transition in its complementary material Ta_(2)NiS_(5)does not show any experimental hints of an excitonic insulating phase.We present a microscopic investigation of the electronic and phononic effects involved in the structural phase transition in Ta_(2)NiSe_(5)and Ta-Niss using extensive first-principles calculations.In both materials the crystal symmetries are broken by phonon instabilities,which in tum lead to changes in the electronic bandstructure also observed in the experiment.A total energy landscape analysis shows no tendency towards a purely electronic instability and we find that a sizeable lattice distortion is needed to open a bandgap.We conclude that an excitonic instability is not needed to explain the phase transition in both Ta_(2)NiSe_(5)and Ta_(2)NiS_(5).