Terahertz wave rectification in a ferroelectric triglycine sulfate single crystal.

The effect of optical rectification (OR) in the terahertz range (THz rectification, TR) is experimentally demonstrated. The effect consists of generating a DC voltage on the faces of a ferroelectric triglycine sulfate (TGS) single crystal under the action of pulsed radiation with a frequency of 1.57 and 1.

Correction to "Terahertz Magnon-Polaritons in TmFeO".

[This corrects the article DOI: 10.1021/acsphotonics.7b01402.

Ferrimagnetic spintronics.

Ferrimagnets composed of multiple and antiferromagnetically coupled magnetic elements have attracted much attention recently as a material platform for spintronics. They offer the combined advantages of both ferromagnets and antiferromagnets, namely the easy control and detection of their net magnetization by an external field, antiferromagnetic-like dynamics faster than ferromagnetic dynamics and the potential for high-density devices. This Review summarizes recent progress in ferrimagnetic spintronics, with particular attention to the most-promising functionalities of ferrimagnets, which include their spin transport, spin texture dynamics and all-optical switching.

Ultrafast demagnetization in a ferrimagnet under electromagnetic field funneling.

The quest to improve the density, speed and energy efficiency of magnetic memory storage has led to the exploration of new ways of optically manipulating magnetism at the ultrafast time scale, in particular in ferrimagnetic alloys. While all-optical magnetization switching is well-established on the femtosecond timescale, lateral nanoscale confinement and thus the potential significant reduction of the size of the magnetic element remains an outstanding challenge. Here we employ resonant electromagnetic energy funneling through plasmon nanoantennas to influence the demagnetization dynamics of a ferrimagnetic TbCo alloy thin film.

Fully Controllable Structural Phase Transition in Thermomechanical Molecular Crystals with a Very Small Thermal Hysteresis.

The construction of a practical crystalline molecular machine faces two challenges: to realize a collective molecular movement, and to amplify this movement into a precisely controlled mechanical response in real time and space. Thermosalient single crystals display cooperative molecular movements that are converted to strong macroscopic mechanical responses or shape deformations during temperature-induced structural phase transitions. However, these collective molecular movements are hard to control once initiated, and often feature thermal hystereses that are larger than 10 °C, which greatly hamper their practical applications.

Robust thermoelastic microactuator based on an organic molecular crystal.

Mechanically responsive molecular crystals that reversibly change shape triggered by external stimuli are invaluable for the design of actuators for soft robotics, artificial muscles and microfluidic devices. However, their strong deformations usually lead to their destruction. We report a fluorenone derivative (4-DBpFO) showing a strong shear deformation upon heating due to a structural phase transition which is reproducible after more than hundred heating/cooling cycles.

Halide Perovskites for Nonlinear Optics.

Halide perovskites provide an ideal platform for engineering highly promising semiconductor materials for a wide range of applications in optoelectronic devices, such as photovoltaics, light-emitting diodes, photodetectors, and lasers. More recently, increasing research efforts have been directed toward the nonlinear optical properties of halide perovskites because of their unique chemical and electronic properties, which are of crucial importance for advancing their applications in next-generation photonic devices. Here, the current state of the art in the field of nonlinear optics (NLO) in halide perovskite materials is reviewed.

Enhanced Second Harmonic Generation from Ferroelectric HfO-Based Hybrid Metasurfaces.

Integrated nonlinear metasurfaces leading to high-efficiency optical second harmonic generation (SHG) are highly desirable for optical sensing, imaging, and quantum photonic systems. Compared to traditional metal-only metasurfaces, their hybrid counterparts, where a noncentrosymmetric nonlinear photonic material is incorporated in the near-field of a metasurface, can significantly boost SHG efficiency. However, it is difficult to integrate such devices on-chip due to material incompatibilities, thickness scaling challenges, and the narrow band gaps of nonlinear optical materials.

Chiral Lead Halide Perovskite Nanowires for Second-Order Nonlinear Optics.

Hybrid organic/inorganic lead halide perovskites (LHPs) have recently emerged as extremely promising photonic materials. However, the exploration of their optical nonlinearities has been mainly focused on the third- and higher-order nonlinear optical (NLO) effects. Strong second-order NLO responses are hardly expected from ordinary LHPs due to their intrinsic centrosymmetric structures, but are highly desirable for advancing their applications in the next generation integrated photonic circuits.

Terahertz Magnon-Polaritons in TmFeO.

Magnon-polaritons are shown to play a dominant role in the propagation of terahertz (THz) waves through TmFeO orthoferrite, if the frequencies of the waves are in the vicinity of the quasi-antiferromagnetic spin resonance mode. Both time-domain THz transmission and emission spectroscopies reveal clear beatings between two modes with frequencies slightly above and slightly below this resonance, respectively. Rigorous modeling of the interaction between the spins of TmFeO and the THz light shows that the frequencies correspond to the upper and lower magnon-polariton branches.

Controlling the Growth of Molecular Crystal Aggregates with Distinct Linear and Nonlinear Optical Properties.

Two novel donor-acceptor molecules, 2,7-diphenylbenzo[1,2-b:4,3-b']difuran-4,5-dicarbonitrile and 2,7-bis(4-methoxyphenyl)benzo[1,2-b:4,3-b']difuran-4,5-dicarbonitrile containing cyano group as the electron acceptor, were synthesized. Their single-crystal structures, molecular packing, and self-assembly behaviors were also investigated. By simple solvent evaporation techniques, these compounds self-assemble into various low-dimensional microstructures that demonstrate distinctive nonlinear optical properties depending on the orientations of their transition dipoles.

All-optical observation and reconstruction of spin wave dispersion.

To know the properties of a particle or a wave, one should measure how its energy changes with its momentum. The relation between them is called the dispersion relation, which encodes essential information of the kinetics. In a magnet, the wave motion of atomic spins serves as an elementary excitation, called a spin wave, and behaves like a fictitious particle.

High-Efficiency Second-Harmonic Generation from Hybrid Light-Matter States.

We report a novel approach to modify the second order nonlinear optical (NLO) susceptibility of organic nanofiber crystals by hybridization with the optical modes of microcavities in the strong coupling regime. The wavelength dependence of the SHG efficiency displays two intense peaks corresponding to the so-formed light-matter hybrid states. Our results demonstrate an enhancement of the resonant SHG efficiency of the lower polariton by 2 orders of magnitude for the collectively coupled molecules as compared to that of the same material outside the microcavity.

Colossal magneto-optical modulation at terahertz frequencies by counterpropagating femtosecond laser pulses in TbGaO.

Single-frequency terahertz modulation of the magneto-optical Faraday effect with a record amplitude of the polarization rotation of ∼0.5° is achieved using a slab of the etalon Faraday rotator crystal TbGaO. The modulation is the result of the interaction of two counterpropagating laser pulses via the optical Kerr effect.

Switching of chiral magnetic skyrmions by picosecond magnetic field pulses via transient topological states.

Magnetic chiral skyrmions are vortex like spin structures that appear as stable or meta-stable states in magnetic materials due to the interplay between the symmetric and antisymmetric exchange interactions, applied magnetic field and/or uniaxial anisotropy. Their small size and internal stability make them prospective objects for data storage but for this, the controlled switching between skyrmion states of opposite polarity and topological charge is essential. Here we present a study of magnetic skyrmion switching by an applied magnetic field pulse based on a discrete model of classical spins and atomistic spin dynamics.

Spectrally resolved optical probing of laser induced magnetization dynamics in bismuth iron garnet.

The spectrally resolved magnetization dynamics in bismuth iron garnet shows a fluence dependent light induced modification of the magneto-optical Faraday spectrum. It is demonstrated that the relative contributions from the tetrahedral and octahedral iron sites to the Faraday spectrum change due to the impact of the pump pulse. This change explains the observed deviation from a linear dependence of the amplitude of the oscillations on the fluence, as expected for the inverse Faraday effect.

Electric field generation of Skyrmion-like structures in a nematic liquid crystal.

Skyrmions are particle-like topological objects that are increasingly drawing attention in condensed matter physics, where they are connected to inversion symmetry breaking and chirality. Here we report the generation of stable Skyrmion-like structures in a thin nematic liquid crystal film on chemically patterned patchy surfaces. Using the interplay of material elasticity and surface boundary conditions, we use a strong electric field to quench the nematic liquid crystal from a fully aligned phase to vortex-like nematic liquid crystal structures, centered on patterned patches, which carry two different sorts of topological defects.

Nanoscale Confinement of All-Optical Magnetic Switching in TbFeCo--Competition with Nanoscale Heterogeneity.

Single femtosecond optical laser pulses, of sufficient intensity, are demonstrated to reverse magnetization in a process known as all-optical switching. Gold two-wire antennas are placed on the all-optical switching film TbFeCo. These structures are resonant with the optical field, and they create a field enhancement in the near-field which confines the area where optical switching can occur.

Channeling Vibrational Energy To Probe the Electronic Density of States in Metal Clusters.

We investigate the electronic density of states (DOS) of isolated neutral cobalt clusters by probing the temperature-modulated population of electronic states through UV photoionization. The temperature is controlled via resonant excitation of lattice vibrations using the free-electron laser FELICE, after which the vibrational and electronic systems equilibrate through the electron-phonon coupling, redistributing the population of electronic states. The data are analyzed by surface photoemission theory, modified to incorporate the realistic DOS.

Orbit and spin resolved magnetic properties of size selected [ConRh]⁺ and [ConAu]⁺ nanoalloy clusters.

Bi-metallic nanoalloys of mixed 3d-4d or 3d-5d elements are promising candidates for technological applications. The large magnetic moment of the 3d materials in combination with a high spin-orbit coupling of the 4d or 5d materials give rise to a material with a large magnetic moment and a strong magnetic anisotropy, making them ideally suitable in for example magnetic storage devices. Especially for clusters, which already have a higher magnetic moment compared to the bulk, these alloys can profit from the cooperative role of alloying and size reduction in order to obtain magnetically stable materials with a large magnetic moment.

Ultrafast all-optical response of a nematic liquid crystal.

Liquid crystals are superior optical materials for large area displays, but it is considered that their collective and slow-millisecond response makes them useless for ultrafast optical applications. In contrast to that, we here demonstrate an ultrafast optical response of a nematic liquid crystal, which is induced by an intense femtosecond optical impulse. We show that the refractive index of the nematic liquid crystal pentyl-cyanobiphenyl can be modulated at a time scale as fast as 500 fs via a coherently excited optical Kerr effect.

Unusual Temperature Dependence of Magnetization and Possible Magnetic Noncollinearity in Tm and Pr Clusters.

Rare-earth metals in their bulk form possess rather similar crystallographic structures, which is due to the very similar features of their outer electronic states. On the other hand, their magnetic properties are of rich variety, which is related to the specific form of the indirect magnetic exchange interaction between the inner electronic shells. In cluster form, this interplay may lead to very unusual magnetic structures.

Extended π-conjugated ruthenium zinc-porphyrin complexes with enhanced nonlinear-optical properties.

Zinc porphyrin dimers and trimers, in which the porphyrins are connected via a ruthenium metal core, exhibit large third-order nonlinear optical absorption coefficients and refractive indices. These properties are a result of the presence of multiple porphyrins, which lead to an extension of the π-conjugated system and the octupolar effect.