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International audience; The familiar dipolar backflow in an electron gas around a slowly moving massive impurity represents, in linear response, the averaged induced current far from the impurity and is proportional to the density response function and the forward scattering amplitude within the Born approximation. Here, we calculate the strength of the dipolar density modulation around a slow proton in three- and two-dimensional paramagnetic electron gases, beyond the perturbative linear-response treatment, by using scattering phase shifts at the Fermi energy which satisfy the Friedel-sum rule. These are determined by solving self-consistently the ground-state Kohn-Sham equations for screening. A sign-changing effect, as a function of the electron gas density, is found in the strength in both dimensions. Using the self-consistent phase shifts, a recently proposed expression for the so-called direct charge in three-dimensional electromigration is also investigated.

International audience; The behavior of minor hysteresis loops in perpendicular anisotropy Co/Pt and Co/Pd multilayers has been investigated. Upon applying a succession of identical magnetic field cycles, we observe a very substantial cumulative growth of the minor loop area. For the Co/Pt multilayers this effect only saturates near complete magnetization reversal while the behavior is slightly more limited for Co/Pd multilayers. We also find this cumulative growth to occur even if the minor loop field cycles are made asymmetric by means of a positive bias field. The cumulative behavior persists up to a sample-dependent threshold value above which this effect disappears. In all samples, the cumulative minor loop growth is correlated with a small reduction in the maximum magnetization value in each cycle. Magneto-optical Kerr microscopy studies correlate the minor loop growth with the memory and cumulative expansion of lateral domain cycling. All experimental observations can be consistently explained as an accumulation of small nucleation domains that aid subsequent reversals and facilitate the cumulative minor loop growth.

The Dzyaloshinskii-Moriya interaction (DMI), which only exists in noncentrosymmetric systems, is responsible for the formation of exotic chiral magnetic states. The absence of DMI in most two-dimensional (2D) magnetic materials is due to their intrinsic inversion symmetry. Here, using first-principles calculations, we demonstrate that significant DMI can be obtained in a series of Janus monolayers of manganese dichalcogenides MnXY in which the difference between X and Y on the opposites sides of Mn breaks the inversion symmetry. In particular, the DMI amplitudes of MnSeTe and MnSTe are comparable to those of state-of-the-art ferromagnet/heavy metal (FM/HM) heterostructures. In addition, by performing Monte Carlo simulations, we find that at low temperatures the ground states of the MnSeTe and MnSTe monolayers can transform from ferromagnetic states with worm-like magnetic domains into the skyrmion states by applying external magnetic field. At increasing temperature, the skyrmion states starts fluctuating above 50 K before an evolution to a completely disordered structure at higher temperature. The present results pave the way for new device concepts utilizing chiral magnetic structures in specially designed 2D ferromagnetic materials., 18 pages, 5 figures

Structurally chiral materials hosting multifold fermions with large topological number have attracted considerable attention because of their naturally long surface Fermi arcs and bulk quantized circular photogalvanic effect (CPGE). Multifold fermions only appear in metallic states, and therefore most studies so far have only focused on the semimetals in compounds with chiral crystal structures. In this work, we show that the structurally chiral topological trivial insulators are also exotic states, which is interesting from the application point of view, owing to their natural advantage to host a large bulk photovoltaic effect in the visible wavelength region. In recent decades, the shift current in the visible wavelength region was limited to be $10\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}{\mathrm{A}/\mathrm{V}}^{2}$ in all the experimentally measured reports. By scanning the insulators with chiral structure, we found a class of compounds with photoconductivity ranging from $\ensuremath{\sim}20$ to $\ensuremath{\sim}80\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}{\mathrm{A}/\mathrm{V}}^{2}$, which is comparable to the largest reported shift current. This work illustrates that the compounds with chiral structure can host both quantum CPGE and a strong shift current in the second-order optical response. Moreover, this work offers a good platform for the study of the shift current and its future application by putting the focus on insulators with chiral lattices, so far overlooked in photovoltaic technologies.