Theory of the Topological Spin Hall Effect in Antiferromagnetic Skyrmions: Impact on Current-Induced Motion

We demonstrate that the nontrivial magnetic texture of antiferromagnetic Skyrmions (AFM Sks) promotes a nonvanishing topological spin Hall effect (TSHE) on the flowing electrons. This effect results in a substantial enhancement of the nonadiabatic torque and, hence, improves the Skyrmion mobility. This nonadiabatic torque increases when decreasing the Skyrmion size, and, therefore, scaling down results in a much higher torque efficiency. In clean AFM Sks, we find a significant boost of the TSHE close to the van Hove singularity. Interestingly, this effect is enhanced away from the band gap in the presence of nonmagnetic interstitial defects. Furthermore, unlike their ferromagnetic counterpart, the TSHE in AFM Sks increases with an increase in the disorder strength, thus opening promising avenues for materials engineering of this effect.

Benefits of EMDR therapy on the memory in the treatment of PTSD

According to some studies, 80% of subjects suffering from post-traumatic stress disorder (PTSD) present twice the risk of developing an insanity as they age because of the high level of stress that has been induced. Indeed, the triggered trauma has a deleterious effect on the establishment of the stress’ axis (the hypothalamic pituitary adrenal axis) which is then not able to regulate itself. As a consequence, the hippocampal neurons will be attacked by an excess of cortisol. Memory's dysfunction is central in the symptomatology of PTSD, particularly in respect to encoding and recall. The hippocampus is able to transfer information to the prefrontal cortex. Actually, subjects with PTSD present less activity in the prefrontal cortex triggered by a decrease of encoding and recall capacities. EMDR therapy (eye movement desensitization and recruitment) allow for a fast relief of symptoms by a bilateral alternate stimulation (SBA). Indeed, saccadic eye movements stem affect related to the traumatic event and process the associated cognitions. During the desensitization phase in EMDR, we noticed an increase in activity of the brain's prefrontal, ventromedial, amygdala and thalamic regions. Indeed, the recall of traumatic memories goes through implicit emotional valence regions and associative areas for which the experience is already deeply integrated. After comparing cerebral activity before and after the therapy, researches on EMDR shows that a reduction of stress’ symptoms has some sensitive link to PTSD (in prevention to dementia).

Disclosure of interest

The authors have not supplied their declaration of competing interest.

Hund's Rule-Driven Dzyaloshinskii-Moriya Interaction at 3d-5d Interfaces

Using relativistic first-principles calculations, we show that the chemical trend of the Dzyaloshinskii-Moriya interaction (DMI) in 3d-5d ultrathin films follows Hund's first rule with a tendency similar to their magnetic moments in either the unsupported 3d monolayers or 3d-5d interfaces. We demonstrate that, besides the spin-orbit coupling (SOC) effect in inversion asymmetric noncollinear magnetic systems, the driving force is the 3d orbital occupations and their spin-flip mixing processes with the spin-orbit active 5d states control directly the sign and magnitude of the DMI. The magnetic chirality changes are discussed in the light of the interplay between SOC, Hund's first rule, and the crystal-field splitting of d orbitals.

Spin-Swapping Transport and Torques in Ultrathin Magnetic Bilayers

Planar spin transport in disordered ultrathin magnetic bilayers comprising a ferromagnet and a normal metal (typically used for spin pumping, spin Seebeck and spin-orbit torque experiments) is investigated theoretically. Using a tight-binding model that puts the extrinsic spin Hall effect and spin swapping on equal footing, we show that the nature of spin-orbit coupled transport dramatically depends on the ratio between the layer thickness d and the mean free path λ. While the spin Hall effect dominates in the diffusive limit (d≫λ), spin swapping dominates in the Knudsen regime (d≲λ). A remarkable consequence is that spin swapping induces a substantial fieldlike torque in the Knudsen regime.

New perspectives for Rashba spin-orbit coupling

In 1984, Bychkov and Rashba introduced a simple form of spin-orbit coupling to explain the peculiarities of electron spin resonance in two-dimensional semiconductors. Over the past 30 years, Rashba spin-orbit coupling has inspired a vast number of predictions, discoveries and innovative concepts far beyond semiconductors. The past decade has been particularly creative, with the realizations of manipulating spin orientation by moving electrons in space, controlling electron trajectories using spin as a steering wheel, and the discovery of new topological classes of materials. This progress has reinvigorated the interest of physicists and materials scientists in the development of inversion asymmetric structures, ranging from layered graphene-like materials to cold atoms. This Review discusses relevant recent and ongoing realizations of Rashba physics in condensed matter.