Electromagnetically tunable spin-valley-polarized current via anomalous Nernst effect in monolayer of jacutingaite.

Monolayer jacutingaite (PtHgSe) exhibits remarkable properties, including significant spin-orbit coupling (SOC) and a tunable band gap, attributed to its buckled honeycomb geometry and the presence of heavy atoms. In this study, we explore the spin- and valley-dependent anomalous Nernst effect (ANE) in jacutingaite under the influence of a vertical electric field, off-resonance circularly polarized light (OCPL), and an antiferromagnetic exchange field. Our findings, within the low-energy approximation, reveal the emergence of a perfectly spin-polarized ANE with the application of appropriate OCPL and a perfectly valley-polarized ANE under an antiferromagnetic exchange field.

Chiral optical solitons in an electrically active multiferroic guiding structure.

A stack of a dielectric planar waveguide with a Kerr-type nonlinearity, sandwiched between two oxide-based helical multiferroic layers is shown to support electrically-controlled chiral solitons. These findings follow from analytical and full numerical simulations. The analytical scheme delivers explicit material parameters for the guided mode soliton and unveils how the soliton propagation characteristics are controlled by tuning the multiferroic helicity and amplitude of the injected electromagnetic wave.

Floquet Engineering the Exceptional Points in Parity-Time-Symmetric Magnonics.

Magnons serve as a testing ground for fundamental aspects of Hermitian and non-Hermitian wave mechanics and are of high relevance for information technology. This study presents setups for realizing spatiotemporally driven parity-time- (PT) symmetric magnonics based on coupled magnetic waveguides and magnonic crystals. A charge current in a metal layer with strong spin-orbit coupling sandwiched between two insulating magnetic waveguides leads to gain or loss in the magnon amplitude depending on the directions of the magnetization and the charge currents.

Tunable chiral photonic cavity based on multiferroic layers.

Realization of externally tunable chiral photonic sources and resonators is essential for studying and functionalizing chiral matter. Here, oxide-based stacks of helical multiferroic layers are shown to provide a suitable, electrically-controllable medium to efficiently trap and filter purely chiral photonic fields. Using analytical and rigorous coupled wave numerical methods we simulate the dispersion and scattering characteristics of electromagnetic waves in multiferroic heterostructures.

Femtosecond Polarization Shaping of Free-Electron Laser Pulses.

We demonstrate the generation of extreme-ultraviolet (XUV) free-electron laser (FEL) pulses with time-dependent polarization. To achieve polarization modulation on a femtosecond timescale, we combine two mutually delayed counterrotating circularly polarized subpulses from two cross-polarized undulators. The polarization profile of the pulses is probed by angle-resolved photoemission and above-threshold ionization of helium; the results agree with solutions of the time-dependent Schrödinger equation.

Magnetoelectric tuning of spin, valley, and layer-resolved anomalous Nernst effect in transition-metal dichalcogenides bilayers.

The anomalous Nernst coefficient (ANC) for transition-metal dichalcogenide (TMD) bilayers is studied with a focus on the interplay between layer pseudospin, spin, and valley degrees of freedom when electric and exchange fields are present. Breaking the inversion and time reversal symmetries via respectively electric and exchange fields results for bilayer TMDs in a spin-valley-layer polarized total ANC. Conditions are determined for controlling the spin, valley, and layer-resolved contributions via electric field tuning.

Spatio-temporal superconducting dynamics driven by THz fields from topological spintronic terahertz emitters.

Metastructures of spintronic THz emitters can be engineered to have a well-defined topology characterized by a topological charge. The emitted THz radiation possesses a phase-locked transversal and longitudinal components with the ratio of which being tunable by the topological charge of the underlying metastructure. The THz fields so produced are employed to drive and spatio-temporally modulate the superconducting order parameter in a type II superconductor.

Imaging and phase-locking of non-linear spin waves.

Non-linear processes are a key feature in the emerging field of spin-wave based information processing and allow to convert uniform spin-wave excitations into propagating modes at different frequencies. Recently, the existence of non-linear magnons at half-integer multiples of the driving frequency has been predicted for NiFe at low bias fields. However, it is an open question under which conditions such non-linear spin waves emerge coherently and how they may be used in device structures.

Thickness-dependent slow light gap solitons in three-dimensional coupled photonic crystal waveguides.

The thickness-dependent multimodal nature of three-dimensional (3D) coupled photonic crystal waveguides is investigated with the aim of realizing a medium for controlled optical gap soliton formation in the slow light regime. In the linear case, spectral properties of the modes (dispersion diagrams), location of the gap regions versus the thickness of the 3D photonic crystal, and the near-field distributions at frequencies in the slow light region are analyzed using a full-wave electromagnetic solver. In the nonlinear regime (Kerr-type nonlinearity), we infer an existence of crystal-thickness-dependent temporal solitons with stable pulse envelope and use the solitonic pulses for driving quantum transitions in localized quantum systems within the photonic crystal waveguide.

Light-Induced Magnetization at the Nanoscale.

Triggering and switching magnetic moments is of key importance for applications ranging from spintronics to quantum information. A noninvasive ultrafast control at the nanoscale is, however, an open challenge. Here, we propose a novel laser-based scheme for generating atomic-scale charge current loops within femtoseconds.

Photonic Signatures of Spin-Driven Ferroelectricity in Multiferroic Dielectric Oxides.

We study the dispersion and scattering properties of electromagnetic modes coupled to a helically ordered spin lattice hosted by a dielectric oxide with a ferroelectric polarization driven by vector spin chirality. Quasianalytical approaches and full-fledged numerics evidence the formation of a chiral magnonic photonic band gap and the presence of gate-voltage dependent circular dichroism in the scattering of electromagnetic waves from the lattice. Gating couples to the emergent ferroelectric polarization and hence, to the underlying vector-spin chirality.

Spin-Resolved Quantum Scars in Confined Spin-Coupled Two-Dimensional Electron Gas.

Quantum scars refer to an enhanced localization of the probability density of states in the spectral region with a high energy level density. Scars are discussed for a number of confined pure and impurity-doped electronic systems. Here, we studied the role of spin on quantum scarring for a generic system, namely a semiconductor-heterostructure-based two-dimensional electron gas subjected to a confining potential, an external magnetic field, and a Rashba-type spin-orbit coupling.

Supercurrent Induced by Chiral Coupling in Multiferroic/Superconductor Nanostructures.

We study the transport and the superconducting dynamics in a layer of type II superconductor (SC) with a normal top layer that hosts a helical magnetic ordering that gives rise to spin-current-driven ferroelectric polarization. Proximity effects akin to this heterostructure result in an anisotropic supercurrent transport and modify the dynamic properties of vortices in the SC. The vortices can be acted upon and controlled by electric gating or other means that couple to the spin ordering in the top layer, which, in turn, alter the superconducting/helical magnet coupling characteristics.

Rotating edge-field driven processing of chiral spin textures in racetrack devices.

Topologically distinct magnetic structures like skyrmions, domain walls, and the uniformly magnetized state have multiple applications in logic devices, sensors, and as bits of information. One of the most promising concepts for applying these bits is the racetrack architecture controlled by electric currents or magnetic driving fields. In state-of-the-art racetracks, these fields or currents are applied to the whole circuit.

Highly Tunable Spin-Orbit Torque and Anisotropic Magnetoresistance in a Topological Insulator Thin Film Attached to Ferromagnetic Layer.

We investigate spin-charge conversion phenomena in hybrid structures of topological insulator thin films and magnetic insulators. We find an anisotropic inverse spin-galvanic effect that yields a highly tunable spin-orbit torque. Concentrating on the quasiballistic limit, we also predict a giant anisotropic magnetoresistance at low dopings.

Steering magnonic dynamics and permeability at exceptional points in a parity-time symmetric waveguide.

Tuning the magneto optical response and magnetic dynamics are key elements in designing magnetic metamaterials and devices. This theoretical study uncovers a highly effective way of controlling the magnetic permeability via shaping the magnonic properties of coupled magnetic waveguides separated by a nonmagnetic spacer with strong spin-orbit interaction (SOI). We demonstrate how a spacer charge current leads to enhancement of magnetic damping in one waveguide and a decrease in the other, constituting a bias-controlled magnetic parity-time (PT) symmetric system at the verge of the exceptional point where magnetic gains/losses are balanced.

Imprinting photon orbital angular momentum during laser-assisted photoemission from quantum wells.

We study theoretically the transfer of the light field orbital angular momentum (OAM) to propagating electrons upon photoemission from quantum well states. Irradiation with a Laguerre-Gaussian mode laser pulse elevates the quantum well state into a laser-dressed Volkov state that can be detected in an angular and energy-resolved manner while varying the characteristics of the driving fields. We derive the photoemission cross section for this process using the S-matrix theory and illustrate how the OAM is embodied in the photoelectron angular pattern with the aid of numerical calculations.

Ultrafast coupled charge and spin dynamics in strongly correlated NiO.

Charge excitations across an electronic band gap play an important role in opto-electronics and light harvesting. In contrast to conventional semiconductors, studies of above-band-gap photoexcitations in strongly correlated materials are still in their infancy. Here we reveal the ultrafast dynamics controlled by Hund's physics in strongly correlated photoexcited NiO.

Topological light fields for highly non-linear charge quantum dynamics and high harmonic generation.

We study theoretically the electron quantum dynamics in atoms driven by intense IR laser pulses that are phase and/or polarization structured. The extremely non-linear electron dynamics causes high harmonic emission, which we calculate, analyze, and characterize. Results are presented for three different types of structured lasers: radially polarized and azimuthally polarized beams and optical skyrmions.

Theory of soliton propagation in nonlinear photonic crystal waveguides.

Propagation of the temporal soliton in Kerr-type photonic crystal waveguide is investigated theoretically and numerically. An expression describing the evolution of the envelope of the soliton based on the full-wave modal analysis, taking into account all space-harmonics, is rigorously obtained. The nonlinear coefficient is derived, for the first time, based on a modification of the refractive indices for each space-harmonic due to the Kerr-type nonlinearity.

Electrical writing, deleting, reading, and moving of magnetic skyrmioniums in a racetrack device.

A magnetic skyrmionium (also called 2π-skyrmion) can be understood as a skyrmion-a topologically nontrivial magnetic whirl-which is situated in the center of a second skyrmion with reversed magnetization. Here, we propose a new optoelectrical writing and deleting mechanism for skyrmioniums in thin films, as well as a reading mechanism based on the topological Hall voltage. Furthermore, we point out advantages for utilizing skyrmioniums as carriers of information in comparison to skyrmions with respect to the current-driven motion.

Twisted magnon beams carrying orbital angular momentum.

Low-energy eigenmode excitations of ferromagnets are spin waves or magnons that can be triggered and guided in magnonic circuits without Ohmic losses and hence are attractive for communicating and processing information. Here we present new types of spin waves that carry a definite and electrically controllable orbital angular momentum (OAM) constituting twisted magnon beams. We show how twisted beams emerge in magnonic waveguides and how to topologically quantify and steer them.

Dynamic Double-Slit Experiment in a Single Atom.

A single-atom "double-slit" experiment is realized by photoionizing rubidium atoms using two independent low power lasers. The photoelectron wave of well-defined energy recedes to the continuum either from the 5P or 6P states in the same atom, resulting in two-path interference imaged in the far field using a photoelectron detector. Even though the lasers are independent and not phase locked, the transitions within the atom impart the phase relationship necessary for interference.

All-optical generation and ultrafast tuning of non-linear spin Hall current.

Spin Hall effect, one of the cornerstones in spintronics refers to the emergence of an imbalance in the spin density transverse to a charge flow in a sample under voltage bias. This study points to a novel way for an ultrafast generation and tuning of a unidirectional nonlinear spin Hall current by means of subpicosecond laser pulses of optical vortices. When interacting with matter, the optical orbital angular momentum (OAM) carried by the vortex and quantified by its topological charge is transferred to the charge carriers.