Accessing Ultrafast Spin-Transport Dynamics in Copper Using Broadband Terahertz Spectroscopy.

We study the spatiotemporal dynamics of ultrafast electron spin transport across nanometer-thick copper layers using ultrabroadband terahertz emission spectroscopy. Our analysis of temporal delays, broadening, and attenuation of the spin-current pulse reveals ballisticlike propagation of the pulse peak, approaching the Fermi velocity, and diffusive features including a significant velocity dispersion. A comparison to the frequency-dependent Fick's law identifies the diffusion-dominated transport regime for distances >2 nm. These findings lay the groundwork for designing future broadband spintronic devices.

Shaping the spin wave spectra of planar 1D magnonic crystals by the geometrical constraints.

We present experimental and numerical studies demonstrating the influence of geometrical parameters on the fundamental spin-wave mode in planar 1D magnonic crystals. The investigated magnonic crystals consist of flat stripes separated by air gaps. The adjustment of geometrical parameters allows tailoring of the spin-wave frequencies. The width of stripes and the width of gaps between them affect spin-wave frequencies in two ways. First, directly by geometrical constraints confining the spin waves inside the stripes. Second, indirectly by spin-wave pinning, freeing the spin waves to a different extent on the edges of stripes. Experimentally, the fundamental spin-wave mode frequencies are measured using an all-optical pump-probe time-resolved magneto-optical Kerr-effect setup. Our studies address the problem of spin-wave confinement and spin-wave dipolar pinning in an array of coupled stripes. We show that the frequency of fundamental mode can be tuned to a large extent by adjusting the width of the stripes and the width of gaps between them.

Quantifying single-platelet biomechanics: An outsider's guide to biophysical methods and recent advances.

Platelets are the key cellular components of blood primarily contributing to formation of stable hemostatic plugs at the site of vascular injury, thus preventing excessive blood loss. On the other hand, excessive platelet activation can contribute to thrombosis. Platelets respond to many stimuli that can be of biochemical, cellular, or physical origin. This drives platelet activation kinetics and plays a vital role in physiological and pathological situations. Currently used bulk assays are inadequate for comprehensive biomechanical assessment of single platelets. Individual platelets interact and respond differentially while modulating their biomechanical behavior depending on dynamic changes that occur in surrounding microenvironments. Quantitative description of such a phenomenon at single-platelet regime and up to nanometer resolution requires methodological approaches that can manipulate individual platelets at submicron scales. This review focusses on principles, specific examples, and limitations of several relevant biophysical methods applied to single-platelet analysis such as micropipette aspiration, atomic force microscopy, scanning ion conductance microscopy and traction force microscopy. Additionally, we are introducing a promising single-cell approach, real-time deformability cytometry, as an emerging biophysical method for high-throughput biomechanical characterization of single platelets. This review serves as an introductory guide for clinician scientists and beginners interested in exploring one or more of the above-mentioned biophysical methods to address outstanding questions in single-platelet biomechanics.

Light-wave dynamic control of magnetism.

The enigmatic interplay between electronic and magnetic phenomena observed in many early experiments and outlined in Maxwell's equations propelled the development of modern electromagnetism1. Today, the fully controlled evolution of the electric field of ultrashort laser pulses enables the direct and ultrafast tuning of the electronic properties of matter, which is the cornerstone of light-wave electronics2-7. By contrast, owing to the lack of first-order interaction between light and spin, the magnetic properties of matter can only be affected indirectly and on much longer timescales, through a sequence of optical excitations and subsequent rearrangement of the spin structure8-16. Here we introduce the regime of ultrafast coherent magnetism and show how the magnetic properties of a ferromagnetic layer stack can be manipulated directly by the electric-field oscillations of light, reducing the magnetic response time to an external stimulus by two orders of magnitude. To track the unfolding dynamics in real time, we develop an attosecond time-resolved magnetic circular dichroism detection scheme, revealing optically induced spin and orbital momentum transfer in synchrony with light-field-driven coherent charge relocation17. In tandem with ab initio quantum dynamical modelling, we show how this mechanism enables the simultaneous control of electronic and magnetic properties that are essential for spintronic functionality. Our study unveils light-field coherent control of spin dynamics and macroscopic magnetic moments in the initial non-dissipative temporal regime and establishes optical frequencies as the speed limit of future coherent spintronic applications, spin transistors and data storage media.

Microscaffolds by Direct Laser Writing for Neurite Guidance Leading to Tailor-Made Neuronal Networks.

While modern day integrated electronic circuits are essentially designed in a 2D fashion, the brain can be regarded as a 3D circuit. The thus enhanced connectivity enables much more complex signal processing as compared to conventional 2D circuits. Recent technological advances in the development of nano/microscale 3D structuring have led to the development of artificial neuron culturing platforms, which surpass the possibilities of classical 2D cultures. In this work, in vitro culturing of neuronal networks is demonstrated by determining predefined pathways through topological and chemical neurite guiding. Tailor-made culturing substrates of microtowers and freestanding microtubes are fabricated using direct laser writing by two-photon polymerization. The first scaffold design that allows for site-specific cell attachment and directed outgrowth of single neurites along defined paths that can be arranged freely in all dimensions, to build neuronal networks with low cell density, is presented. The neurons cultured in the scaffolds show characteristic electrophysiological properties of vital cells after 10 d in vitro. The introduced scaffold design offers a promising concept for future complex neuronal network studies on defined neuronal circuits with tailor-made design specific neurite connections beyond 2D.

Electrical conductivity of InN nanowires and the influence of the native indium oxide formed at their surface.

The electrical properties of InN nanowires were investigated in four-point probe measurements. The dependence of the conductance on the wire diameter allows distinguishing between "core" bulk (quadratic) and "shell" sheet (linear) contributions. Evidence of the formation of a thin In(2)O(3) layer at the surface of the nanowires is provided by X-ray core level photoemission spectroscopy. The shell conductivity is therefore ascribed to an electron accumulation layer forming at the radial InN/In(2)O(3) interface. Although conductance through the accumulation layer dominates for nanowires below a critical diameter of about 55 nm, the core channel cannot be neglected, even for small nanowires.