We address the question of the nonlinearity of the electronic stopping power of slow helium ions in aluminum by measuring the energy distributions and yields of electron emission under the impact of $0.2–4.5\mathrm{keV}{}^3\mathrm{H}{\mathrm{e}}^{+}$ and ${}^4\mathrm{H}{\mathrm{e}}^{+}$ ions. Electron emission experiments can provide an alternative point of view to resolve controversial issues often arising in stopping power measurements. The comparison between two isotopes allows one to distinguish between the energy and velocity dependent emission mechanisms, and indicates that the reported nonlinear velocity dependence of the electronic stopping power can be attributed to residual nuclear stopping effects.

The preparations of single (monolayer) and bulk carbides on the $\mathrm{Mo}\left(110\right)$ and $\mathrm{Mo}\left(100\right)$ single crystals are followed in situ at 1200 K using synchrotron-based high-resolution x-ray photoelectron spectroscopy of the $\mathrm{C}1s$ and core Mo $3d_{5/2}$ levels. By comparing the experimental results to first principles calculations using density functional theory, we suggest real-space surface structures for the carbide-modified surfaces. For a monolayer carbide on $\mathrm{Mo}\left(110\right)$, carbon dimers adsorb in the long-bridge site, most likely at a coverage of $3/8\mathrm{ML}$ carbon atoms per Mo surface atom. For the bulk carbide, we find a coverage of $\sim 0.5\mathrm{ML}$ on the surface, and the calculations show that single carbon atoms are more stable than dimers on the surface. The monolayer carbide on $\mathrm{Mo}\left(100\right)$ exhibits a coverage of $\sim 1\mathrm{ML}$ and agrees with previous studies, while the bulk carbide preparation probably leads to a faceting of the surface.

In this work we show analytically and numerically that the localized regime of wave transport can be modeled as position-dependent diffusion with a diffusion coefficient that retains the memory of the source location. The dependence on the source diminishes when absorption is introduced.

We present a microscopic theory for magnetization relaxation in metallic ferromagnets of nanoscopic dimensions that is based on the calculation of the dynamic spin response matrix in the presence of spin-orbit coupling. Our approach takes into account the collective character of spin excitations in ferromagnetic metals. We show that calculations of the Gilbert damping based on a mean-field, adiabatic approximation fail to describe the relaxation of collective excitations in the ballistic regime. Namely, we show that collective spin excitations such as the ferromagnetic resonance mode have finite damping rates even for perfectly crystalline systems, whereas existing microscopic approaches, based on adiabatic and mean-field approximations, predict infinite damping rates. Moreover, we demonstrate that within a finite frequency approach the relaxation properties are not completely determined by the transverse susceptibility alone, and that the damping rate has a non-negligible frequency dependence in experimentally relevant situations. Our results indicate that the widely used adiabatic approach for spin dynamics breaks down for metallic nanostructures in the presence of strong spin-orbit coupling.

Crystal structure and magnetic ordering in ${\mathrm{YMn}}_3{\mathrm{Al}}_4{\mathrm{O}}_{12}$ are determined by neutron powder diffraction measurement, indicating that $S=2$ spins of the $A^{\prime }$-site ${\mathrm{Mn}}^{3+}$ ions are ordered in G-type antiferromagnetic (AFM) arrangement in the $Im\overline{3}$ cubic crystal structure. Using the first-principles electronic structure calculations, it is found that the AFM spin structure is stabilized by the nearest-neighbour (NN) exchange interaction. The underlying mechanism of the NN exchange is revealed to be the antiferromagnetic Mn-O-Mn superexchange interaction from the calculations of electronic transfer integrals.

Hall effect and magnetoresistance have been measured on single crystals of the parent phase NaFeAs under a uniaxial pressure. Although significant difference of the in-plane resistivity ${\rho }_{xx}(I\parallel a)$ and ${\rho }_{xx}(I\parallel b)$ with the uniaxial pressure along the $b$ axis was observed, the transverse resistivity ${\rho }_{xy}$ shows a surprisingly isotropic behavior. Detailed analysis reveals that the Hall coefficient $R_{\mathrm{H}}$ measured in the two orthogonal configurations $(I\parallel a$ axis and $I\parallel b$ axis) coincide very well and exhibit a deviation from the high temperature background at around the structural transition temperature $T_{\mathrm{s}}$. Furthermore, the magnitude of $R_{\mathrm{H}}$ increases remarkably below the structural transition temperature. This enhanced Hall coefficient is accompanied by the nonlinear transverse resistivity versus magnetic field and enhanced magnetoresistance, which can be explained very well by the two-band model with anisotropic mobilities of each band. Our results together with the two-band model analysis clearly show that the anisotropic in-plane resistivity in the nematic state is closely related to the distinct quasiparticle mobilities when they are moving parallel or perpendicular to the direction of the uniaxial pressure.

We provide a fresh perspective on the pseudogap physics for attractive fermions as described by the three-dimensional Hubbard model. The pseudogap in the single-particle spectral function, which occurs for temperatures above the critical temperature $T_c$ of the superfluid transition, is often interpreted in terms of preformed uncondensed pairs. Here we show that the occurrence of pseudogap physics can be consistently understood as due to local excitations which lead to a splitting of the quasiparticle peak for sufficiently large interaction. This effect becomes prominent at intermediate and high temperatures when the quantum-mechanical hopping is incoherent. We demonstrate the absence of the conjectured pairing temperature below which pseudogap physics is expected to occur. Our results are based on approximating the physics of the three-dimensional Hubbard model by dynamical mean-field theory calculations and a momentum independent self-energy. Our predictions can be tested with ultracold atoms in optical lattices with currently available temperatures and spectroscopic techniques.

The irreversibility of the martensite transition in magnetic shape memory alloys (MSMAs) with respect to the external magnetic field is one of the biggest challenges that limits their application as giant caloric materials. This transition is a magnetostructural transition that is accompanied with a steep drop in magnetization (i.e.,$\mathrm{\Delta }M$) around the martensite start temperature $\left({\mathrm{M}}_{\mathrm{s}}\right)$ due to the lower magnetization of the martensite phase. In this Rapid Communication, we show that $\mathrm{\Delta }M$ around ${\mathrm{M}}_{\mathrm{s}}$ in Mn-rich Ni-Mn-based MSMAs gets suppressed by two orders of magnitude in crushed powders due to the stabilization of the martensite phase at temperatures well above ${\mathrm{M}}_{\mathrm{s}}$ and the austenite finish $\left({\mathrm{A}}_{\mathrm{f}}\right)$ temperatures due to residual stresses. Analysis of the intensities and the FWHM of the x-ray powder-diffraction patterns reveals stabilized martensite phase fractions as $97\%, 75\%$, and $90\%$ with corresponding residual microstrains as $5.4\%, 5.6\%$, and $3\%$ in crushed powders of the three different Mn-rich Ni-Mn alloys, namely, $\mathrm{M}{\mathrm{n}}_{1.8}\mathrm{N}{\mathrm{i}}_{1.8}\mathrm{I}{\mathrm{n}}_{0.4}, \mathrm{M}{\mathrm{n}}_{1.75}\mathrm{N}{\mathrm{i}}_{1.25}\mathrm{Ga}$, and $\mathrm{M}{\mathrm{n}}_{1.9}\mathrm{N}{\mathrm{i}}_{1.1}\mathrm{Ga}$, respectively. Even after annealing at 773 K, the residual stress stabilized martensite phase does not fully revert to the equilibrium cubic austenite phase as the magnetostructural transition is only partially restored with a reduced value of $\mathrm{\Delta }M$. Our results have a very significant bearing on the application of such alloys as inverse magnetocaloric and barocaloric materials.

Topological Majorana fermion (MF) quasiparticles have been recently suggested to exist in semiconductor quantum wires with proximity induced superconductivity and a Zeeman field. Although the experimentally observed zero bias tunneling peak and a fractional ac-Josephson effect can be taken as necessary signatures of MFs, neither of them constitutes a sufficient “smoking gun” experiment. Since one pair of Majorana fermions share a single conventional fermionic degree of freedom, MFs are in a sense fractionalized excitations. Based on this fractionalization we propose a tunneling experiment that furnishes a nearly unique signature of end state MFs in semiconductor quantum wires. In particular, we show that a “teleportation”-like experiment is not enough to distinguish MFs from pairs of MFs, which are equivalent to conventional zero energy states, but our proposed tunneling experiment, in principle, can make this distinction.

We theoretically study the spin and charge generations along with the electron transport on a disordered surface of a doped three-dimensional topological insulator/magnetic insulator junction by using Green's function techniques. We find that the spin and charge currents are induced by not only local, but also nonlocal magnetization dynamics through nonmagnetic impurity scattering on the disordered surface of the doped topological insulator. We also clarify that the spin current as well as charge density are induced by spatially inhomogeneous magnetization dynamics, and the spin current diffusively propagates on the disordered surface. Using these results, we discuss both local and nonlocal spin torques before and after the spin and spin-current generations on the surface, and provide a procedure to detect the spin current.

Density-functional calculations are used to verify the atomic structure of the hexagonal $\mathrm{In}/\mathrm{Si}\left(111\right)-(\sqrt{7}\times \sqrt{3})$ surface, which has been considered to represent an ultimate two-dimensional (2D) limit of metallic In overlayers. Contrary to the prevailing assumption, this surface consists of not a single layer but a double layer of In atoms, which corresponds to a hexagonal deformation of the well-established rectangular In double layer formed on $\mathrm{Si}\left(111\right)-(\sqrt{7}\times \sqrt{3})$ [Park and Kang, Phys. Rev. Lett. 109, 166102 (2012)]. The same double-layer thickness accounts well for the typical coexistence of the hexagonal and rectangular phases and their similar 2D electronic structures. It is thus conclusive that, regardless of rectangular or hexagonal, the $\mathrm{In}/\mathrm{Si}\left(111\right)-(\sqrt{7}\times \sqrt{3})$ surface does not represent a one-atom-thick In overlayer.

We report on a theoretical study of the magnetodipolar coupling and synchronization between two vortex-based spin-torque nano-oscillators (STVOs). In this work we study the dependence of the coupling efficiency on the relative magnetization parameters of the vortices in the system. This study is performed in order to propose an optimized configuration of the vortices for synchronizing STVOs. For this purpose, we combine micromagnetic simulations, the Thiele equation approach, and the analytical macrodipole approximation model to identify the optimized configuration for achieving phase-locking between neighboring oscillators. Notably, we compare vortices configurations with parallel (P) core polarities and with opposite (AP) core polarities. We demonstrate that the AP core configuration exhibits a coupling strength about three times higher than in the P core configuration.

The electronic properties of monolayer phosphorene are exotic due to its puckered structure and large intrinsic direct band gap. We derive and discuss its band structure in the presence of a perpendicular magnetic field. Further, we evaluate the magneto-optical Hall and longitudinal optical conductivities as functions of temperature, magnetic field, and Fermi energy, and show that they are strongly influenced by the magnetic field. The imaginary part of the former and the real part of the latter exhibit regular interband oscillations as functions of the frequency $\omega$ in the range $\hslash \omega \sim 1.5–2\mathrm{eV}$. Strong intraband responses in the latter and weak ones in the former occur at much lower frequencies. The magneto-optical response can be tuned in the microwave-to-terahertz and visible frequency ranges in contrast with a conventional two-dimensional electron gas or graphene in which the response is limited to the terahertz regime. This ability to isolate carriers in an anisotropic structure may make phosphorene a promising candidate for new optical devices.

Recently it has been proposed that a unitary topological mirror symmetry can stabilize multiple zero energy Majorana fermion modes in one-dimensional (1D) time-reversal (TR) invariant topological superconductors. Here we establish an exact equivalence between 1D “topological mirror superconductivity” and chiral topological superconductivity in the BDI class which can also stabilize multiple Majorana-Kramers pairs in 1D TR invariant topological superconductors. The equivalence proves that topological mirror superconductivity can be understood as chiral superconductivity in the BDI symmetry class coexisting with time-reversal symmetry. Furthermore, we show that the mirror Berry phase coincides with the chiral winding invariant of the BDI symmetry class, which is independent of the presence of the time-reversal symmetry. Thus, the time-reversal invariant topological mirror superconducting state may be viewed as a special case of the BDI symmetry class in the well-known Altland-Zirnbauer periodic table of free fermionic phases. We illustrate the results with the examples of 1D spin-orbit coupled quantum wires in the presence of nodeless $s_{\pm }$ superconductivity and the recently discussed experimental system of ferromagnetic atom (Fe) chains embedded on a lead (Pb) superconductor.

The growth of Cu on Ag(100) is investigated by low-temperature scanning tunneling microscopy. Exchange diffusion of Cu deposited onto Ag(100) leads to small pure Cu islands and larger islands consisting of a CuAg alloy in room temperature growth. The ratio of the different types of islands depends on terrace widths up to 100 nm. This surprisingly long-range dependence is correlated to the density of the surface alloy. We thus reveal that the exchange diffusion barrier is influenced by terrace widths far beyond quantum size confinement.

The atomic structure of ultrathin iron films deposited on the (0001) surface of the topological insulator ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ is analyzed by surface x-ray absorption spectroscopy. Iron atoms deposited on a ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ (0001) surface kept at 160 K substitute bismuth atoms within the first quintuple layer. Iron atoms are neighbored by six selenium atoms at a distance in the 2.4 Å range indicating substantial atomic relaxations. Mild annealing up to 520 K leads to the formation of $\alpha$-FeSe, characterized by a local order extending up to the sixth shell (5.80 Å). Ab initio calculations predict a noncollinear magnetic ordering with a transition temperature of 3.5–10 K depending on the iron concentration and the number of the layers in which Fe is located.

The electronic structure of thallium rhenium oxide (${\mathrm{TlReO}}_4$) at room temperature is explored as a function of applied pressure using a diamond-anvil cell and high-resolution x-ray absorption spectroscopy. We show possible evidence of charge transfer from the thallium to the rhenium atom in the high-pressure phase of this compound, thus suggesting a previous proposition made several decades ago. This study provides further insight into the nature of high-pressure phase transitions in ${\mathrm{ABO}}_4$ type compounds.

The consequences of nonlinear anisotropic damping, driven by the presence of Rashba spin-orbit coupling in thin ferromagnetic metals, are examined for the dynamics of topological magnetic solitons such as domain walls, vortices, and skyrmions. The damping is found to affect Bloch and Néel walls differently in the steady-state regime below Walker breakdown and leads to a monotonic increase in the wall velocity above this transition for large values of the Rashba coefficient. For vortices and skyrmions, a generalization of the damping tensor within the Thiele formalism is presented. It is found that chiral components of the damping affect vortexlike and hedgehoglike skyrmions in different ways, but the dominant effect is an overall increase in the viscouslike damping.

Owing to the recent progress on endowing the electronic structure of magnetic nanowires with topological properties, the associated topological solitons in the magnetic texture—magnetic domain walls—appear as very natural hosts for exotic electronic excitations. Here, we propose to use the magnetic domain walls to engender Majorana fermions, which has several notable advantages compared to the existing approaches. First of all, the local tunneling density-of-states anomaly associated with the Majorana zero mode bound to a smooth magnetic soliton is immune to most of parasitic artifacts associated with the abrupt physical ends of a wire, which mar the existing experimental probes. Second, a viable route to move and braid Majorana fermions is offered by domain-wall motion. In particular, we envision the recently demonstrated heat-current induced motion of domain walls in insulating ferromagnets as a promising tool for nonintrusive displacement of Majorana modes. This leads us to propose a feasible scheme for braiding domain walls within a magnetic nanowire network, which manifests the nob-Abelian exchange statistics within the Majorana subspace.

We used a micromechanical torsional oscillator to measure the magnetic response of a twinned ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ single crystal disk near the Bose glass transition. We observe an anomaly in the temperature dependence of the magnetization consistent with the appearance of a magnetic shielding perpendicular to the correlated pinning of the twin boundaries. This effect is related to the thermodynamic transition from the vortex liquid phase to a Bose glass state.