Narrow Results

Porphyrins and related compounds are basic moieties which upon photoexcitation produce paramagnetic transients important to many processes in biology, material science and light–energy conversion. This short review demonstrates the application of time-resolved EPR spectroscopy to two processes in which the photoexcited singlet and/or triplet are involved: (1) intramolecular electron transfer in photoexcited donor–acceptor systems embedded in liquid crystals, where the porphyrins are the electron donors attached to different types of acceptors; and (2) intermolecular magnetic interactions between photoexcited porphyrin triplets and free radicals. In both systems the electron spin plays an important part with regards to the route of the magnetic interactions involved.

When monolayer (ML) MoS₂ is placed on a substrate, the proximity-induced interactions such as the Rashba spin-orbit coupling (RSOC) and exchange interaction (EI) can be introduced. Thus, the electronic system can behave like a spintronic device. In this study, we present a theoretical study on how the presence of the RSCO and EI can lead to the band splitting, the lifting of the valley degeneracy and to the spin polarization in $n$- and $p$-type ML MoS₂. We find that the maxima of the in-plane spin orientation in the conduction and valence bands in ML MoS₂ depend on the Rashba parameter and the effective Zeeman field factor. At a fixed Rashba parameter, the minima of the split conduction band and the maxima of the split valence band along with the spin polarization in ML MoS₂ can be tuned effectively by varying the effective Zeeman field factor. On the basis that the EI can be induced by placing the ML MoS₂ on a ferromagnetic substrate or by magnetic doping in ML MoS₂, we predict that the interesting spintronic effects can be observed in $n$- and $p$-type ML MoS₂. This work can be helpful to gain an in-depth understanding of the basic physical properties of ML MoS₂ for application in advanced electronic and optoelectronic devices.

We investigate the degree of spin polarization of single top quarks in the eγ collision via the process with center-of-mass energies , 1 and 1.5 TeV of the parental linear e⁺e^- collider. Dominant spin fractions and spin asymmetries for the various top quark spin bases are investigated. We show that e⁺-beam direction is the favorite top quark spin decomposition axis. It is found to be comparable with the ones in pp and ep collisions.

Standard relativistic hydrodynamics has been successful in describing the properties of the strongly interacting matter produced in the heavy-ion collision experiments. Recently, there has been a significant theoretical advancement in this field to explain spin polarization of hadrons emitted in these processes. Although current models have successfully explained some of the experimental data based on the coupling between spin polarization and vorticity of the medium, they still lack a clear understanding of the differential measurements. This is commonly interpreted as an indication that the spin needs to be treated as an independent degree of freedom whose dynamics is not entirely bound to flow circulation. In particular, if the spin is a macroscopic property of the system, in equilibrium its dynamics should follow hydrodynamic laws. Here, we develop a framework of relativistic hydrodynamics which includes spin degrees of freedom from the quantum kinetic theory for Dirac fermions and use it for modeling the dynamics of matter. Following experimental observations, we assume that the polarization effects are small and derive conservation laws for the net baryon current, the energy–momentum tensor and the spin tensor based on the de Groot–van Leeuwen–van Weert definitions of these currents. We present various properties of the spin polarization tensor and its components, analyze the propagation properties of the spin polarization components, and derive the spin-wave velocity for arbitrary statistics. We find that only the transverse spin components propagate, analogously to the electromagnetic waves. Finally, using our framework, we study the space–time evolution of the spin polarization for the systems respecting certain space–time symmetries and calculate the mean spin polarization per particle, which can be compared to the experimental data. We find that, for some observables, our spin polarization results agree qualitatively with the experimental findings and other model calculations.

We have determined the spin polarized density of states (DOS) of 3-d amorphous Gd_xSi_1-x in the quantum critical regime of a tunable Metal-Insulator Transition (MIT). Using a spin polarized BCS DOS we fit the data and extract the spin polarization P.

We study the magnetization and the magnetic phases of II-VI-based n-doped non-magnetic-semiconductor (NMS) / narrow to wide dilute-magnetic-semiconductor (DMS) / n-doped NMS quantum wells under in-plane magnetic field. The parallel magnetic field is used as a tool, in order to achieve non-step-like density of states in these -appropriate for conduction-band spintronics- structures.

The current induced local spin polarization due to weak Rashba spin-orbit coupling in narrow strip is studied. In the presence of longitudinal charge current, local spin polarizations appear in the sample. The spin polarization perpendicular to the plane has opposite sign near the two edges. The in-plane spin polarization in the direction perpendicular to the sample edges also appears, but does not change sign across the sample. From our scaling analysis based on increasing the strip width, the out-of-plane spin polarization is important mainly in a system of mesoscopic size, and thus appears not to be associated with the spin-Hall effect in bulk samples.

The intrinsic spin Hall effect has been attracting increasing theoretical and experimental interest since its discovery about two years ago. In this article, we review the main achievements in the theoretical aspect of both dissipative and nondissipative spin Hall effects in mesoscopic systems. The Landauer–Büttiker formula and Green's function approach based numerical method for the spin Hall effect is also introduced.

In a biased two-dimensional electron gas, the presence of spin-orbit coupling of both the Rashba and Dresselhaus type leads to a Hall conductivity of charge carriers in the absence of an external magnetic field. We study the dynamical charge-Hall effect, the field-induced spin accumulation, and the magnetoelectric effect for a system with short-range elastic impurity scattering by analytically solving the kinetic equations for the spin-density matrix in the linear response regime. By tuning the strength of the Rashba and Dresselhaus spin-orbit coupling as well as the frequency and direction of the applied electric field, eigenmodes of the spin-coupled system are identified.

The spin-galvanic effect and the inverse effect, which yeilds current induced spin polarization, in low dimensional semiconductor structures are reviewed. Both effect are caused by asymmetric spin relaxation in systems with lifted spin degeneracy due to k-linear terms in the Hamiltonian.

A spin-rotation symmetry in spin-orbit coupled two-dimensional electron systems gives rise to a long-lived spin excitation that is robust against short-range impurity scattering. The influence of a constant in-plane electric field on this persistent spin helix is studied. To probe the field-induced eigen-modes of the spin-charge coupled system, a surface acoustic wave is exploited that provides the wave-vector for resonant excitation. The approach takes advantage of methods worked out in the field of space-charge waves. Sharp resonances in the field dependence of the in-plane and out-of-plane magnetization are identified.

We theoretically present the spin-dependent electron transport in a two-dimensional electron gas (2DEG) with finite width modulated by magnetic–electric barriers. It is found that the transmission probability and the spin polarization are strongly dependent on the height of the electric barrier, the energy of the incident electron, the distance between the two magnetic fields, and the width of the 2DEG. These may be useful for making the practical devices.

Cu-induced spin polarization in tris(8-hydroxyquinoline) aluminum $({\mathrm{\text{Alq}}}_3)$ has been studied by first-principles calculation. The entanglement between an electron transfer from Cu to ${\mathrm{\text{Alq}}}_3$ and a structural distortion of the ${\mathrm{\text{Alq}}}_3$ molecule gives rise to a strong spin polarization in this originally nonmagnetic molecule ${\mathrm{\text{Alq}}}_3$. The calculated total magnetic moment mainly resides on the ${\mathrm{\text{Alq}}}_3$ molecule $(0.6{\mu }_B)$, while that on Cu is moderate $(0.4{\mu }_B)$. The finding of a spin polarization induced by the nonmagnetic element Cu is helpful for understanding of spin-related phenomenon in ${\mathrm{\text{Alq}}}_3$ and potentially enabling future magnetic-metal-free organic spintronics.

The magnetic properties of bis(8-hydroxyquinoline)copper (${\mathrm{\text{CuQ}}}_2$) were investigated by experiments and first-principles density functional theory (DFT) calculations. The as-prepared ${\mathrm{\text{CuQ}}}_2$ film shows paramagnetic behavior. After annealing in air, room temperature ferromagnetic (FM) properties were found in ${\mathrm{\text{CuQ}}}_2$ film. The Fourier transform infrared spectroscopy (FTIR) analysis indicates a new vibrational mode related to out of plane O–H bend in the annealed film. DFT calculations show that the energy difference between the FM and the antiferromagnetic (AFM) states is greatly increased after O doping, which may be responsible for the room temperature ferromagnetism in the annealed ${\mathrm{\text{CuQ}}}_2$ film.

In this paper, we investigated the spin-dependent electron transport in a nonmagnetic nanostructure under the influence of the $\delta$-doping which can be experimentally doped in the nanostructure with metal-organic chemical vapor deposition or molecular beam epitaxy. The numerical results indicate that the large spin polarization nearly 100% can be achieved in such a structure without the external magnetic field due to spin–orbit interactions and it can be controlled not only by the barrier, but also by the $\delta$-doping. These interesting finds are very valuable for designing the $\delta$-doping-tunable spintronic device based on the nonmagnetic nanostructure.

In the present work, we propose that a one-dimensional quantum heterostructure composed of magnetic and non-magnetic (NM) atomic sites can be utilized as a spin filter for a wide range of applied bias voltage. A simple tight-binding framework is given to describe the conducting junction where the heterostructure is coupled to two semi-infinite one-dimensional NM electrodes. Based on transfer matrix method, all the calculations are performed numerically which describe two-terminal spin-dependent transmission probability along with junction current through the wire. Our detailed analysis may provide fundamental aspects of selective spin transport phenomena in one-dimensional heterostructures at nanoscale level.

Based on density functional theory (DFT), the spin polarization properties of a thiophene molecule which is adsorbed at Fe (100) surface are discussed. A variety of horizontal and vertical adsorption configurations as well as their influences on the spin density distributions are studied in detail. The spin polarization comes from the $p$-$d$ orbital coupling between the thiophene molecule and the electrode, which leads to the molecules’ energy level shifting and the density of states (DOS) broadening, so the two spin states near the Fermi level are exchange split. It is also found that the interfacial spin polarization is different under different contact configurations, and the biggest one will be obtained when the S atom is directly placed above the Fe atom at the horizontal direction. On the other hand, interface spin inversion can be obtained by adjusting the adsorption position, which will be helpful to build spin sensors.

We theoretically investigate the electron transport properties in a nanostructure modulated by a ferromagnetic stripe (FM) and a Schottky metal stripe (SM) as well as a $\delta$-doping with the help of transfer-matrix method. It is found that the position and the weight of the $\delta$-doping, the width of the SM and the electrical potential, all play an important role in the electron transmission probability and the spin polarization. Therefore, we can control the electron transport properties through adjusting the SM and the $\delta$-doping. These interesting phenomena may be very helpful for designing the spintronic devices.

We theoretically investigate dwell time for electrons in a magnetic nanostructure with a $\delta$-doping, which is formed on $\mathrm{\text{InAs}}/{\mathrm{\text{Al}}}_x{\mathrm{\text{In}}}_{1-x}\mathrm{\text{As}}$ heterostructure by depositing a ferromagnetic (FM) stripe. We find that dwell time depends strongly on electron-spins owing to Zeeman coupling and broken symmetry. We also demonstrate that spin-polarized dwell time can be manipulated by $\delta$-doping. Thus, electron spins can be separated in time dimension and such a magnetic nanostructure can be employed as a structurally-controllable temporal spin splitter for spintronics device applications.

The effects of electro-magnetic confining potentials and the s–d exchange interaction between substituted Mn ions and carriers on the spin polarization of carriers in an diluted magnetic semiconductor quantum dot are investigated within the framework of the effective-mass theory. The energy eigenvalues and wavefunctions of a single electron in the presence of an external magnetic field are studied by solving the one particle Schrödinger equation including the conventional Zeeman effect, the s–d exchange interaction and the electric confining potential which describes the dot. The eigenenergy structure for low lying states is strongly dependant on the relative sizes of the s–d exchange interactions and the conventional Zeeman energy splitting. When the spin splitting exceeds the cyclotron energy splitting, the Landau level overlappings occur so that the spin polarization of carriers is induced in low lying energy states. This spin polarization of carriers in the diluted magnetic semiconductor quantum dot can be controlled by changing the electro-magnetic confining potentials.