Skyrmion Hall Effect Revealed by Direct Time-Resolved X-Ray Microscopy

Magnetic skyrmions are highly promising candidates for future spintronic applications such as skyrmion racetrack memories and logic devices. They exhibit exotic and complex dynamics governed by topology and are less influenced by defects, such as edge roughness, than conventionally used domain walls. In particular, their finite topological charge leads to a predicted "skyrmion Hall effect", in which current-driven skyrmions acquire a transverse velocity component analogous to charged particles in the conventional Hall effect. Here, we present nanoscale pump-probe imaging that for the first time reveals the real-time dynamics of skyrmions driven by current-induced spin orbit torque (SOT). We find that skyrmions move at a well-defined angle {\Theta}_{SH} that can exceed 30{\deg} with respect to the current flow, but in contrast to theoretical expectations, {\Theta}_{SH} increases linearly with velocity up to at least 100 m/s. We explain our observation based on internal mode excitations in combination with a field-like SOT, showing that one must go beyond the usual rigid skyrmion description to unravel the dynamics.Comment: pdf document arxiv_v1.1. 24 pages (incl. 9 figures and supplementary information

Field-free deterministic ultra fast creation of skyrmions by spin orbit torques

Magnetic skyrmions are currently the most promising option to realize current-driven magnetic shift registers. A variety of concepts to create skyrmions were proposed and demonstrated. However, none of the reported experiments show controlled creation of single skyrmions using integrated designs. Here, we demonstrate that skyrmions can be generated deterministically on subnanosecond timescales in magnetic racetracks at artificial or natural defects using spin orbit torque (SOT) pulses. The mechanism is largely similar to SOT-induced switching of uniformly magnetized elements, but due to the effect of the Dzyaloshinskii-Moriya interaction (DMI), external fields are not required. Our observations provide a simple and reliable means for skyrmion writing that can be readily integrated into racetrack devices

Inertia-driven resonant excitation of a magnetic skyrmion

Topological spin structures such as magnetic domain walls, vortices, and skyrmions, have been receiving great interest because of their high potential application in various spintronic devices. To utilize them in the future spintronic devices, it is first necessary to understand the dynamics of the topological spin structures. Since inertial effect plays a crucial role in the dynamics of a particle, understanding the inertial effect of topological spin structures is an important task. Here, we report that a strong inertial effect appears steadily when a skyrmion is driven by an oscillating spin-Hall-spintorque (SHST). We find that the skyrmion exhibits an inertia-driven hypocycloid-type trajectory when it is excited by the oscillating SHST. This motion has not been achieved by an oscillating magnetic field, which only excites the breathing mode without the inertial effect. The distinct inertial effect can be explained in terms of a spin wave excitation in the skyrmion boundary which is induced by the non-uniform SHST. Furthermore, the inertia-driven resonant excitation provides a way of experimentally estimating the inertial mass of the skyrmion. Our results therefore pave the way for the development of skyrmion-based device applications

Emergent Phenomena Induced by Spin-Orbit Coupling at Surfaces and Interfaces

Spin-orbit coupling (SOC) describes the relativistic interaction between the spin and momentum degrees of freedom of electrons, and is central to the rich phenomena observed in condensed matter systems. In recent years, new phases of matter have emerged from the interplay between SOC and low dimensionality, such as chiral spin textures and spin-polarized surface and interface states. These low-dimensional SOC-based realizations are typically robust and can be exploited at room temperature. Here we discuss SOC as a means of producing such fundamentally new physical phenomena in thin films and heterostructures. We put into context the technological promise of these material classes for developing spin-based device applications at room temperature

Spin-orbit torque-driven skyrmion dynamics revealed by time-resolved X-ray microscopy

Magnetic skyrmions are topologically protected spin textures with attractive properties suitable for high-density and low-power spintronic device applications. Much effort has been dedicated to understanding the dynamical behaviours of the magnetic skyrmions. However, experimental observation of the ultrafast dynamics of this chiral magnetic texture in real space, which is the hallmark of its quasiparticle nature, has so far remained elusive. Here, we report nanosecond-dynamics of a 100nm-diameter magnetic skyrmion during a current pulse application, using a time-resolved pump-probe soft X-ray imaging technique. We demonstrate that distinct dynamic excitation states of magnetic skyrmions, triggered by current-induced spin-orbit torques, can be reliably tuned by changing the magnitude of spin-orbit torques. Our findings show that the dynamics of magnetic skyrmions can be controlled by the spin-orbit torque on the nanosecond time scale, which points to exciting opportunities for ultrafast and novel skyrmionic applications in the future.clos

Tunable Klein-like tunnelling of high-temperature superconducting pairs into graphene

Superconductivity can be induced in a normal material via the 'leakage' of superconducting pairs of charge carriers from an adjacent superconductor. This so-called proximity effect is markedly influenced by graphene's unique electronic structure, both in fundamental and technologically relevant ways. These include an unconventional form1,2 of the 'leakage' mechanism- the Andreev reflection3-and the potential of supercurrent modulation through electrical gating4. Despite the interest of high-temperature superconductors in that context5,6, realizations have been exclusively based on low-temperature ones. Here we demonstrate a gate-tunable, high-temperature superconducting proximity effect in graphene. Notably, gating effects result fromthe perfect transmission of superconducting pairs across an energy barrier-a form of Klein tunnelling7,8, up to nowobserved only for non-superconducting carriers9,10- and quantum interferences controlled by graphene doping. Interestingly, we find that this type of interference becomesdominant without the need of ultraclean graphene, in stark contrast to the case of low-temperature superconductors11. These results pave the way to a new class of tunable, high-temperature Josephson devices based on large-scale graphene