Spintronic THz emitters (STEs) rely on spin current acceleration or decay, resulting in a burst of broadband THz emission, offering a new route to THz optics. Here, we demonstrate novel metastructures of STEs for molding the vectorial focal distribution of the emitted THz radiations. The metastructures also allow controlling the characteristics of local fields. Performing combined micromagnetic-electromagnetic simulations, we demonstrate the generation of broadband THz fields with designed vectorial, chiral, magnetic, or topological features and discuss the potential of these fields for studying magnetic, multiferroic, and chiral structures. The STEs metastructure is shown to produce higher-order electric and magnetic multipoles as well as localized, longitudinal, broadband magnetoelectric THz pulses. Furthermore, subwavelength features of the near fields at a distance less than 10 μm can be tuned by steering the magnetization of the metastructure. The results point to a new type of engineered STEs for the generation of structured broadband THz fields, with potential applications in the fields of optoelectronics, optics, and ultrafast magnetism.

We consider the magnonic properties of two dipolarly coupled magnetic stripes, both deposited on a normal conductive substrate with strong spin-orbit coupling. A charge current in the substrate acts on the adjacent magnets with spin-orbit torques, which result in magnonic damping or antidamping of the spin waves, and hence a gain-loss coupling of the two magnetic stripes. The whole setup is demonstrated to exhibit features typical for parity-time (PT) symmetric systems.Phenomena are demonstrated that can be functionalized in magnonic devices, including reconfigurable magnonic diodes and logic devices. Alternative stripes designs and PT-symmetric, periodic, coupled magnonic textures are studied. Analytical and full numerical analysis identify the conditions for the appearance of exceptional points (EPs), where magnonic gain and loss are balanced and evidence nonreciprocal magnon propagation and enhanced magnon excitation around EPs. Furthermore, the dipolar coupling is shown to bring in a wave vector-dependent PT-symmetric behavior. Proposing and simulating a PT-symmetric magnonic crystal, we show how EPs and hence associated phenomena can be steered to a particular wave vector in a gaped spectrum via material design. The phenomena offer additional tools for magnonic-based communication and computational devices.

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. Calculating the high energy spectrum for each spin channel and corresponding states, as well as employing statistical methods known for the spinless case, we showed that spin-dependent scarring occurs in a spin-coupled electronic system. Scars can be spin mixed or spin polarized and may be detected via transport measurements or spin-polarized scanning tunneling spectroscopy.

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. The results may be useful for applications in optical communications, multiplexing systems, nonlinear physics, and ultrafast spectroscopy.

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. The results point to a new type of time-resolved spectroscopy, in which the electronic orbital motion is addressed exclusively, with the potential for a new insight in spin-orbitally or orbitally coupled systems.