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Defects play significant roles in spin-current-related physical processes in intrinsic ferromagnetic semiconductors (FMSs), which are great promise for spintronics applications. However, current defect calculation methods cannot be used to investigate charged defects in FMSs due to the spin polarization of both the charged defect states and ionized carriers, which is not well treated in current defect calculation methods. In order to solve this problem, we propose a spin-distinguishable charge correction (SDCC) method that uses spin-polarized band edge charge density instead of spin-unpolarized uniform background charge density as the compensating charge for charged defects. We apply our method to study the defect properties of CrI3 monolayer and find it can be doped n-type under the Cr-rich growth condition but difficult to be doped p-type. The SDCC method proposed here is generally suitable for all FMSs, which will be useful for the studies of defect properties of magnetic semiconductors. [ABSTRACT FROM AUTHOR]

Defects play significant roles in spin-current-related physical processes in intrinsic ferromagnetic semiconductors (FMSs), which are great promise for spintronics applications. However, current defect calculation methods cannot be used to investigate charged defects in FMSs due to the spin polarization of both the charged defect states and ionized carriers, which is not well treated in current defect calculation methods. In order to solve this problem, we propose a spin-distinguishable charge correction (SDCC) method that uses spin-polarized band edge charge density instead of spin-unpolarized uniform background charge density as the compensating charge for charged defects. We apply our method to study the defect properties of CrI3 monolayer and find it can be doped n-type under the Cr-rich growth condition but difficult to be doped p-type. The SDCC method proposed here is generally suitable for all FMSs, which will be useful for the studies of defect properties of magnetic semiconductors. [ABSTRACT FROM AUTHOR]

We study the symmetry of spin transport in graphene with the Rashba spin–orbit coupling (SOC) and the staggered potential, which can be produced by depositing the graphene on a transition-metal dichalcogenides substrate. The results show that all three spin polarization components along the x , y and z directions are achieved with a measurable conductance in such a nonmagnetic graphene. The spin transport property near the two valleys is discussed in the light of the symmetry of the system. Both conductance and spin polarization present some certain symmetries with respect to the Rashba SOC (RSOC) and staggered potential. The system could work as a valley-spin polarization transverter which combines valleytronics and spintronics. Furthermore, the asymmetric Fano–Rashba resonance of the conductance and spin polarization could occur in a resonant structure due to interference of spin-polarized discrete and continuum states induced by the RSOC. The Fano–Rashba resonance can be effectively controlled by the gate voltage. The derived symmetry relations and numerical results could provide a guideline for the design of spin-valley-based devices.

The spin effect of electrons/positrons (e−/e+) and polarization effect of γ photons are investigated in the interaction of two counter-propagating linearly polarized laser pulses of peak intensity 8.9 × 1023 W cm−2 with a thin foil target. The processes of nonlinear Compton scattering and nonlinear Breit–Wheeler pair production based on the spin- and polarization-resolved probabilities are implemented into the particle-in-cell (PIC) algorithm by Monte Carlo methods. It is found from PIC simulations that the average degree of linear polarization of emitted γ photons can exceed 50%. This polarization effect leads to a reduced positron yield by about 10%. At some medium positron energies, the reduction can reach 20%. Furthermore, we also observe that the local spin polarization of e−/e+ leads to a slight decrease of the positron yield about 2% and some anomalous phenomena about the positron spectrum and photon polarization at the high-energy range, due to spin-dependent photon emissions. Our results indicate that spin and polarization effects should be considered in calculating the pair production and laser-plasma interaction with the laser power of 10 PW to 100 PW classes. [ABSTRACT FROM AUTHOR]

We propose a correction to the coefficient of nuclear spin diffusion by a factor , where is the average nuclear spin polarization. The correction, derived by extending the Lowe–Gade theory to low-temperature cases, implies that transportation of nuclear magnetization through nuclear spin diffusion accelerates when the system is hyperpolarized, whereas for low polarization the correction factor approaches unity and the diffusion coefficient coincides with the conventional diffusion coefficient valid in the high-temperature limit. The proposed scaling of the nuclear spin diffusion coefficient can lead to observable effects in the buildup of nuclear polarization by dynamic nuclear polarization. [ABSTRACT FROM AUTHOR]

In a previous paper we showed how higher-order strong-field-QED processes in long laser pulses can be approximated by multiplying sequences of 'strong-field Mueller matrices'. We obtained expressions that are valid for arbitrary field shape and polarization. In this paper we derive practical approximations of these Mueller matrices in the locally-constant- and the locally-monochromatic-field regimes. The spin and polarization can also change due to loop contributions (the mass operator for electrons and the polarization operator for photons). We derive Mueller matrices for these as well, for arbitrary laser polarization and arbitrarily polarized initial and final particles. [ABSTRACT FROM AUTHOR]

While the spin of two-dimensional polarization states admits a simple representation, its physical interpretation for three-dimensional (3D) mixed polarization states requires a more involved analysis. In this work, we address the spin structure of the electric field of a general 3D polarization state by taking advantage of the characteristic decomposition and the recently introduced notion of nonregularity associated with 3D states. We show that a nonregular polarization state necessarily has an additional spin component due to the state's genuinely 3D nature, and both the orientation and magnitude of the spin are regulated by the degree of nonregularity. The results provide new physical insight into partially polarized evanescent and tightly focused light fields in which strong nonregular character has recently been demonstrated. [ABSTRACT FROM AUTHOR]

Different approaches for considering barrier crossing times are analyzed, with special emphasis on recent experiments which attempt to measure what is commonly referred to as the Larmor tunneling time. We show that that these experiments cannot reveal the Larmor time, due to the finite energy width of the incident particles. The Larmor time, which measures changes in spin polarization, is classified together with other measurements such as the Buttiker–Landauer oscillating barrier time as indirect measurements of interaction times of scattered particles. In contrast, we present a direct quantum mechanical measure of a barrier crossing time taken to be the difference between the mean flight time for a particle transmitted through a potential barrier incident on a screen and the time it would take to reach the same screen without the barrier. These metrics are asymptotic, in the sense that they infer a time from a measurement after the scattering event is over, whereas other measures like the dwell time are local. Some time measures are well-defined only for incident states which are monochromatic in energy, others are well-defined also for incident wavepackets whose incident energy width is finite. In this paper we compare the different approaches to conclude that only the flight time can be used to answer the provocative (but ultimately ill-posed) question: how much time does it take to tunnel through a barrier? [ABSTRACT FROM AUTHOR]

We report a new type of spin–orbit coupling (SOC) called geometric SOC. Starting from the relativistic theory in curved space, we derive an effective nonrelativistic Hamiltonian in a generic curve embedded into flat three dimensions. The geometric SOC is O(m−1), in which m is the electron mass, and hence much larger than the conventional SOC of O(m−2). The energy scale is estimated to be a hundred meV for a nanoscale helix. We calculate the current-induced spin polarization in a coupled-helix model as a representative of the chirality-induced spin selectivity. We find that it depends on the chirality of the helix and is of the order of 0.01ℏ per nm when a charge current of 1 μA is applied. [ABSTRACT FROM AUTHOR]

This paper investigates the spin characteristics of photoelectrons when hydrogen-like ions are centro-symmetrically irradiated with converging vector waves—a non-paraxial form of structured light. For a photon with given total angular momentum and third component thereof, photoelectrons with both helicities are obtained—in contrast to the fixed helicities produced by left- or right-circularly polarized light. The angular distribution of photoelectrons is broadly tunable through the radiation mode numbers, and opposite helicities can be extracted in synchronism.

Spin-transfer torque (STT) applications in magnetization switching such as magnetic tunnel junctions (MTJs) have been of popular interest in the development of novel memory technologies. However, the high switching power associated with these is a critical disadvantage in the operation of typical magnesium oxide (MgO)-based STT-MTJs. In this study, an ultra-low switching power, only 10% of the MgO-based MTJs, is achieved by high-purity spin polarization current using a superlattice-barrier MTJ with half-metallic magnets. The resistance-area product of the device is reduced to 0.2 Ω μm2, which is less than 10% of that in traditional MgO-based MTJs. The proposed MTJ has a higher performance, including STT and required switching current. A decrease in the switching power could avoid not only the disadvantages of power dissipation but also the device endurance due to lower Joule heating in the proposed MTJs. [ABSTRACT FROM AUTHOR]

We theoretically study the inverse Faraday effect, i.e., the optical induction of spin polarization with circularly polarized light, by particularly focusing on effects of band dispersions and Fermi surfaces in crystal systems with the spin–orbit interaction (SOI). By numerically solving the time-dependent Schrödinger equation of a tight-binding model with the Rashba-type SOI, we reproduce the light-induced spin polarization proportional to where E0 and ω are the electric-field amplitude and the angular frequency of light, respectively. This optical spin induction is attributed to dynamical magnetoelectric coupling between the light electric field and the electron spins mediated by the SOI. We elucidate that the magnitude and sign of the induced spin polarization sensitively depend on the electron filling. To understand these results, we construct an analytical theory based on the Floquet theorem. The theory successfully explains the dependencies on E0 and ω and ascribes the electron-filling dependence to a momentum-dependent effective magnetic field governed by the Fermi-surface geometry. Several candidate materials and experimental conditions relevant to our theory and model parameters are also discussed. Our findings will enable us to engineer the magneto-optical responses of matters via tuning the material parameters. [ABSTRACT FROM AUTHOR]

That the rates and yields of reactions of organic radicals can be spin dependent is well known in the context of the radical pair mechanism (RPM). Less well known, but still well established, is the chiral-induced spin selectivity (CISS) effect in which chiral molecules act as spin filters that preferentially transmit electrons with spins polarized parallel or antiparallel to their direction of motion. Starting from the assumption that CISS can arise in electron transfer reactions of radical pairs, we propose a simple way to include CISS in conventional models of radical pair spin dynamics. We show that CISS can (a) increase the sensitivity of radical pairs to the direction of a weak external magnetic field, (b) change the dependence of the magnetic field effect on the reaction rate constants, and (c) destroy the field-inversion symmetry characteristic of the RPM. We argue that CISS polarization effects could be observable by EPR (electron paramagnetic resonance) of oriented samples either as differences in continuous wave, time-resolved spectra recorded with the spectrometer field parallel or perpendicular to the CISS quantization axis or as signals in the in-phase channel of an out-of-phase ESEEM (electron spin echo envelope modulation) experiment. Finally we assess whether CISS might be relevant to the hypothesis that the magnetic compass of migratory songbirds relies on photochemically-formed radical pairs in cryptochrome flavoproteins. Although CISS effects offer the possibility of evolving a more sensitive or precise compass, the associated lack of field-inversion symmetry has not hitherto been observed in behavioural experiments. In addition, it may no longer be safe to assume that the observation of a polar magnetic compass response in an animal can be used as evidence against a radical pair sensory mechanism.

In this study, we investigate the electron transport properties of a B-doped armchair graphene nanoribbon (AGNR) suspended between graphene electrodes based on first-principles calculations. Our calculations reveal that one of the electron transmission channels of a pristine AGNR junction is closed by the B-doping. We then proceed to explore the effect of the B-doping on the spin-polarized electron transport behavior of a Fe-functionalized AGNR junction. As a result, transmission channels for majority-spin electrons are closed and the spin polarization of the electron transmission is enhanced from 0.60 for the Fe-functionalized AGNR junction to 0.96 for the B- and Fe-codoped one. This observation implies that the codoped AGNR junction can be employed as a spin filter. In addition, we investigate the electronic nature of the transmission suppression caused by the B-doping. A detailed analysis of the scattering wave functions clarifies that a mode modulation of an incident wave arises in the B-doped AGNR part and the incident wave connects to an evanescent wave in the transmission-side electrode. For pristine and Fe-functionalized AGNR junctions, such a mode modulation is not observed and the incident wave connects to a propagating wave in the transmission-side electrode. Tuning of electron transport property by exploiting such a mode modulation is one of promising techniques for designing functionality of spintronics devices. We also discuss the general correspondence between the electron transmission spectrum and the density of states of a junction.

The occurrence of any physical process is restricted by the constraints imposed by the laws of thermodynamics on the energy and entropy exchange involved. A prominent class of processes where thermodynamic constraints are crucial involve polarization of nuclear spin baths that are at the heart of magnetic resonance imaging, nuclear magnetic resonance (NMR), quantum information processing. Polarizing a spin bath, is the key to enhancing the sensitivity of these tools, leading to new analytical capabilities and improved medical diagnostics. In recent years, significant effort has been invested in identifying the far-reaching consequences of quantum modifications to classical thermodynamics for such processes. Here we focus on the adverse role of quantum correlations (entanglement) in the spin bath that can impede its cooling in many realistic scenarios. We propose to remove this impediment by modified cooling schemes, incorporating probe-induced disentanglement or, equivalently, alternating non-commuting probe–bath interactions to suppress the buildup of quantum correlations in the bath. The resulting bath polarization is thereby exponentially enhanced. The underlying quantum thermodynamic principles have far-reaching implications for a broad range of quantum technological applications.

We theoretically study the inverse Faraday effect, i.e., the optical induction of spin polarization with circularly polarized light, by particularly focusing on effects of band dispersions and Fermi surfaces in crystal systems with the spin–orbit interaction (SOI). By numerically solving the time-dependent Schrödinger equation of a tight-binding model with the Rashba-type SOI, we reproduce the light-induced spin polarization proportional to ${E}_{0}^{2}/{\omega }^{3}$ where E _0 and ω are the electric-field amplitude and the angular frequency of light, respectively. This optical spin induction is attributed to dynamical magnetoelectric coupling between the light electric field and the electron spins mediated by the SOI. We elucidate that the magnitude and sign of the induced spin polarization sensitively depend on the electron filling. To understand these results, we construct an analytical theory based on the Floquet theorem. The theory successfully explains the dependencies on E _0 and ω and ascribes the electron-filling dependence to a momentum-dependent effective magnetic field governed by the Fermi-surface geometry. Several candidate materials and experimental conditions relevant to our theory and model parameters are also discussed. Our findings will enable us to engineer the magneto-optical responses of matters via tuning the material parameters.

The spin polarization of topological surface states is of high interest for possible applications in spintronics. At present, the only technique capable to measure the surface state spin texture is spin and angle resolved photoemission spectroscopy (SARPES). However, values reported by SARPES differed strongly. An established technique to measure the spin polarization of ferromagnetic materials is the so-called Meservey–Tedrow technique, which is based on spin dependent tunneling from a superconducting electrode to a ferromagnet. Here, we theoretically investigate how the Meservey–Tedrow technique can be adapted to topological insulators. We demonstrate that with a specific device geometry it is possible to determine the in-plane component of the spin polarization of topological surface states. More complex device geometries can access the full momentum dependence of the spin polarization. We also show that it is possible to extract the spin-flip scattering rate of surface electrons with the same devices.

We experimentally demonstrate high degree of polarization of ^13 C nuclear spins weakly interacting with nitrogen-vacancy (NV) centers in diamond. We combine coherent microwave excitation pulses with optical illumination to provide controlled relaxation and achieve a polarity-tunable, fast nuclear polarization of degree higher than 85% at room temperature for remote ^13 C nuclear spins exhibiting hyperfine interaction strength with NV centers of the order of 600 kHz. We show with the aid of numerical simulation that the anisotropic hyperfine tensor components naturally provide a route to control spin mixing parameter so that highly efficient nuclear polarization is enabled through careful tuning of nuclear quantization axis by external magnetic field. We further discuss spin dynamics and wide applicability of this method to various target ^13 C nuclear spins around the NV center electron spin. The proposed control method demonstrates an efficient and versatile route to realize, for example, high-fidelity spin register initialization and quantum metrology using nuclear spin resources in solids.

Tunnel ionization of noble gas atoms driven by a strong circularly polarized laser field in combination with a counter-rotating second harmonic generates spin-polarized electrons correlated to the spin-polarized ionic core. Crucially, such two-color field can bring the spin-polarized electrons back to the parent ion, enabling the scattering of the spin-polarized electron on the spin-polarized parent ion. Here we show how one can control the degree of spin polarization as a function of electron energy and recollision time by tuning the laser parameters, such as the relative intensities of the counter-rotating fields. The attosecond precision of the control over the degree of spin polarization opens the door for attosecond control and spectroscopy of spin-resolved dynamics.

The spin polarization of carbon nanotubes (CNTs) offers a tunable building block for spintronic devices and is also crucial for realizing carbon-based electronics. However, the effect of chiral CNTs is still unclear. In this paper, we use the density functional theory (DFT) method to investigate the spin polarization of a series of typical finite-length chiral CNTs (9, m). The results show that the spin density of chiral CNTs (9, m) decreases gradually with the increase in m and vanishes altogether when m is larger than or equal to 6. The armchair edge units on both ends of the (9, m) CNTs exhibit a clear inhibition of spin polarization, allowing control of the spin density of (9, m) CNTs by adjusting the number of armchair edge units on the tube end. Furthermore, analysis of the orbitals shows that the spin of the ground state for (9, m) CNTs mainly comes from the contributions of the frontier molecular orbitals (MOs), and the energy gap decreases gradually with the spin density for chiral CNTs. Our work further develops the study of the spin polarization of CNTs and provides a strategy for controlling the spin polarization of functional molecular devices through chiral vector adjustment.

We explore the electronic properties and exciton effects in short graphene nanoribbons (SGNRs), which have two armchair edges and two zigzag edges. Our results show that both of these two types of edges have profound effects on the electronic properties and exciton effects. Both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) states are alternatively changed between the bulk and the edge states as the lengths of the zigzag edges increase, due to the competition between the states of the two types of edges. The energy gaps, as a function of the lengths of the armchair edges, will then induce two kinds of trends. Furthermore, two kinds of exciton energies and exciton binding energies are found, which can be understood through the two kinds of HOMO and LUMO states in SGNRs. In addition, we find that the three triplet exciton states are not totally energy degenerate in SGNRs due to the spin-polarized states on the zigzag edges.

We inserted non-magnetic layers of Au and Cu into sputtered AlO-based magnetic tunnel junctions and Meservey–Tedrow junctions in order to study their effect on tunnelling magnetoresistance (TMR) and spin polarization (TSP). When either Au or Cu are inserted into a Co/AlO interface, we find that TMR and TSP remain finite and measurable for thicknesses up to several nanometres. High-resolution transmission electron microscopy shows that the Cu and Au interface layers are fully continuous when their thickness exceeds ∼3nm, implying that spin-polarized carriers penetrate the interface noble metal to distances exceeding this value. A power law model based on exchange scattering is found to fit the data better than a phenomenological exponential decay. The discrepancy between these length scales and the much shorter ones reported from x-ray magnetic circular dichroism studies of magnetic proximitization is ascribed to the fact that our tunnelling transport measurements selectively probe s-like electrons close to the Fermi level. When a 0.1 nm thick Cu or Au layer is inserted within the Co, we find that the suppression of TMR and TSP is restored on a length scale of ≲1nm, indicating that this is a sufficient quantity of Co to form a fully spin-polarized band structure at the interface with the tunnel barrier. [ABSTRACT FROM AUTHOR]

Spin-resolved photoemission is one of the most direct ways of measuring the magnetization of a ferromagnet. If all valence band electrons contribute, the measured average spin polarization is proportional to the magnetization. This is even the case if electronic excitations are present, and thus is of particular interest for studying the response of the magnetization to a pump laser pulse. Here, we demonstrate the feasibility of ultrafast spin-resolved photoemission using free electron laser (FEL) radiation and investigate the effect of space charge on the detected spin polarization. The sample is exposed to the radiation of the FEL FLASH in Hamburg. Surprisingly, the measured spin polarization depends on the fluence of the FEL radiation: a higher FEL fluence reduces the measured spin polarization. Space-charge simulations can explain this effect. These findings have consequences for future spin-polarized photoemission experiments using pulsed photon sources. [ABSTRACT FROM AUTHOR]

We develop a theory of spin-dependent phenomena in the streaming regime characterized by ballistic acceleration of electrons in the moderate electric field until they achieve the optical phonon energy and abruptly emit phonons. It is shown that the Dyakonov–Perel spin relaxation is drastically modified in this regime, the current-induced spin orientation remarkably increases, reaches a high value ≈2% in the electric field ∼1 kV cm−1 and falls with further increase in the field. The spin polarization enhancement is caused by squeezing of the electron momentum distribution in the direction of drift. We also predict field-induced oscillatory dynamics of spin polarization of the photocarriers excited into the conduction band by a short circularly polarized optical pulse. [ABSTRACT FROM AUTHOR]

We have studied the spin-dependent electronic properties of the interface formed between epitaxial Co thin films deposited on Cu(001) and the experimental molecule tris-(9-oxidophenalenone)-aluminum(III) (Al(OP)3), created as a variation of the prototypical organic semiconductor Alq3 to tailor the spin filtering properties by modifying chemisorption with cobalt. The interfaces have been grown under ultra-high vacuum conditions by progressive deposition of 0.5–5 nm Al(OP)3 on the freshly prepared cobalt substrate. For every growth step we have monitored the energy level alignment at the interface as well as the spin polarization of the occupied manifold by spin-resolved photoemission spectroscopy. We identify two hybrid interface states in the energy window of 2 eV below the Fermi energy. The first is at 0.9 eV below EF and shows an 8% higher spin polarization than Co, while the second is at 1.6 eV below EF and shows a spin polarization reduced by 4%. [ABSTRACT FROM AUTHOR]

We demonstrate opto-spintronics using Fe-doped Indium Phosphide (InP). The method is based on optical orientation of InP conduction electron spins which are electrically detected in planar InP/oxide/Ni tunnel spin filters. We separate the optical excitation from electrical detection, avoiding thus additional interactions of photons with the ferromagnet. Interface engineering provides a surface iron accumulation and semiconducting Fe:In _2 O _3 in the oxide tunnel barrier. The spin filtering effect switches to positive or negative asymmetry, depending on the Fe concentration in Fe _x :InP. With respect to the Fe-like electronic structure of these oxides, we can explain the opposite spin selection mechanisms as interface effects. In the temperature region where the InP mobility peaks, we find a maximum of spin-dependent asymmetry of $\sim 9\%$ in semi-insulating Fe:InP (001), and show the electrical spin detection in hyperpolarized InP also at room temperature. Such robust electronic spin detection in an InP nanodevice is planned to complement dynamic nuclear polarization experiments.

Using the full-potential linearized augmented plane wave method, we have explored the structural, electronic band structure, binding energy, and magnetic properties of a non-magnetic impurity (Al, Si, S, and Cl) doped phosphorene layer. The binding energy showed a tendency to decrease with increasing atomic number. Nonetheless, we still found large binding energies of 5.1 eV ∼ 8.3 eV. We observed that the electronic band structure and magnetic property were strongly dependent on the specific impurity atom. For instance, we propose that the Al doped system will show a semiconducting transport property. In all other systems, we found metallic band structures. We predict that the Al and Si impurity act as donor elements whereas the S and Cl impurities behave as acceptor elements. Interestingly, the magnetic state appeared in Si, S, and Cl doped systems while the Al impurity induced no spin polarized state. In the Si doped system, the major contribution to a magnetic moment originated from Si impurity itself, while the presence of dangling bonds at a neighboring P atom near the impurity site plays a crucial role for magnetism in S and Cl doped systems. On the other hand, interestingly, we observed a half metallic feature in the S doped layer. Overall, we have found that the magnetic state can be manipulated by even non-magnetic impurity doping in a phosphorene layer.

The characteristic transition of the ${\rm N}{{{\rm V}}^{-}}$ centre at 637 nm is between $^{3}{{A}_{2}}$ and $^{3}E$ triplet states. There are also intermediate $^{1}{{A}_{1}}$ and $^{1}E$ singlet states, and the infrared transition at 1042 nm between these singlets is studied here using uniaxial stress. The stress shift and splitting parameters are determined, and the physical interaction giving rise to the parameters is considered within the accepted electronic model of the centre. It is established that this interaction for the infrared transition is due to a modification of electron–electron Coulomb repulsion interaction. This is in contrast to the visible 637 nm transition where shifts and splittings arise from modification to the one-electron Coulomb interaction. It is also established that a dynamic Jahn–Teller interaction is associated with the singlet $^{1}E$ state, which gives rise to a vibronic level 115 cm ^−1 above the $^{1}E$ electronic state. Arguments associated with this level are used to provide experimental confirmation that the $^{1}{{A}_{1}}$ is the upper singlet level and $^{1}E$ is the lower singlet level.

We present a quantitative, systematic study of the polarization of the Zeeman magnetic sublevels of the NV-defect in diamond as a function of magnetic field alignment relative to the NV-defect axis. The orientation dependence of NV-polarization in the lab frame is accounted for by a Wigner rotation of a constant defect frame polarization. We also find that the NV-defect level polarizations vary with the P1 defect concentration, and that the polarization of the m _s = 0 state with optical pumping decreases from 46% to 36% in samples as P1 concentrations vary from 20 ppm to 100 ppm, respectively.

We extend the covariance matrix description of atom–light quantum interfaces, originally developed for real and effective spin-1/2 atoms, to include ‘spin alignment’ degrees of freedom. This allows accurate modelling of optically probed spin-1 ensembles in arbitrary magnetic fields. We also include technical noise terms that are very common in experimental situations. These include magnetic field noise, variable atom number and the effect of magnetic field inhomogeneities. We demonstrate the validity of our extended model by comparing numerical simulations to a free–induction decay measurement of polarized 87Rb atoms in the f = 1 ground state. We qualitatively and quantitatively reproduce experimental results with no free parameters. The model can be easily extended to larger spin systems, and adapted to more complicated experimental situations. [ABSTRACT FROM AUTHOR]

Using the numerical renormalization group method, we study the spin thermopower in the two-channel spin-1/2 Kondo model. The non-Fermi liquid properties related to the overscreening of the impurity spin crucially affect the response of the system to the magnetic field and in consequence the spin-thermal transport. Although the magnetic field does not strongly polarize the impurity spin, we show that it nevertheless strongly affects the low-energy part of the spectral function. In turn, this leads to characteristic saturation of the spin Seebeck coefficient at the value of 0.388kB/|e| at T ∼ T*, where T*∝B2/TK is the scale of the crossover between the intermediate-temperature non-Fermi-liquid regime and the low-temperature Fermi-liquid regime. We show that measuring the spin thermopower at low magnetic fields would provide a sensitive test for distinguishing regular Fermi liquid, singular Fermi liquid and non-Fermi liquid behaviour in nanodevices. [ABSTRACT FROM AUTHOR]

We have found and characterized, by angle-resolved photoelectron spectroscopy (ARPES), quasi-one-dimensional spin-split states in chain-like surface alloys formed by large Z elements (Bi and Pb) at the Cu(110) surface. The ARPES results are supported by first-principles relativistic calculations, which also confirm the spin polarization of these states, characteristic of the Rashba–Bychkov effect. The Fermi surface contours are open, but warped, as a result of the interaction with the bulk Cu conduction band. This interaction introduces a k dependence of the spin splitting perpendicular to the chains direction. We have also investigated the influence of the atomic spin–orbit parameter in substitutional isostructural Bi1−xPbx overlayers, and found that the magnitude of the spin splitting can be continuously tuned as a function of stoichiometry. [ABSTRACT FROM AUTHOR]

We propose a scheme of band engineering by means of staggered electric potential, antiferromagnetic exchange field and intrinsic spin-orbit coupling for electrons on a honeycomb lattice. With fine control on the degrees of freedom of spin, sublattice and valley, one can achieve a topological state with simultaneous non-zero charge and spin Chern numbers. With first principles calculations, we confirm that the scheme can be realized by material modification in perovskite G-type antiferromagnetic insulators grown along the [111] direction, where Dirac electrons from d orbits are achieved on an atomic sheet of a buckled honeycomb lattice. In a finite sample, this state provides a spin-polarized quantum edge current, robust to both non-magnetic and magnetic defects, with the spin polarization reversible by electric field, and is thus ideal for spintronics applications. [ABSTRACT FROM AUTHOR]

We inserted non-magnetic layers of Au and Cu into sputtered AlO $_{x}$ -based magnetic tunnel junctions and Meservey–Tedrow junctions in order to study their effect on tunnelling magnetoresistance (TMR) and spin polarization (TSP). When either Au or Cu are inserted into a Co/AlO $_{x}$ interface, we find that TMR and TSP remain finite and measurable for thicknesses up to several nanometres. High-resolution transmission electron microscopy shows that the Cu and Au interface layers are fully continuous when their thickness exceeds $\sim 3\;\text{nm}$ , implying that spin-polarized carriers penetrate the interface noble metal to distances exceeding this value. A power law model based on exchange scattering is found to fit the data better than a phenomenological exponential decay. The discrepancy between these length scales and the much shorter ones reported from x-ray magnetic circular dichroism studies of magnetic proximitization is ascribed to the fact that our tunnelling transport measurements selectively probe s -like electrons close to the Fermi level. When a 0.1 nm thick Cu or Au layer is inserted within the Co, we find that the suppression of TMR and TSP is restored on a length scale of $\lesssim 1\;\text{nm}$ , indicating that this is a sufficient quantity of Co to form a fully spin-polarized band structure at the interface with the tunnel barrier.

We formulate the effective Hamiltonian of Rashba spin–orbit coupling (RSOC) in (LAO/STO) heterostructures. We derive analytical expressions of properties, e.g. Rashba parameter, effective mass, band edge energy and orbital occupancy, as functions of material and tunable heterostructure parameters. While linear RSOC is dominant around the Γ-point, cubic RSOC becomes significant at the higher-energy anti-crossing region. We find that linear RSOC stems from the structural inversion asymmetry (SIA), while the cubic term is induced by both SIA and bulk asymmetry. Furthermore, the SOC strength shows a striking dependence on the tunable heterostructure parameters such as STO thickness and the interfacial electric field which is ascribed to the quantum confinement effect near the LAO/STO interface. The calculated values of the linear and cubic RSOC are in agreement with previous experimental results. [ABSTRACT FROM AUTHOR]

With the creation of nitrogen (NV) in 1b diamond it is common to find that the absorption and emission is predominantly of negatively charged NV centres. This occurs because electrons tunnel from the substitutional nitrogen atoms to NV to form NV−–N+ pairs. There can be a small percentage of neutral charge NV0 centres and a linear increase of this percentage can be obtained with optical intensity. Subsequent to excitation it is found that the line width of the NV− zero-phonon has been altered. The alteration arises from a change of the distribution of N+ ions and a modification of the average electric field at the NV− sites. The consequence is a change to the Stark shifts and splittings giving the change of the zero-phonon line (ZPL) width. Exciting the NV− centres enhances the density of close N+ ions and there is a broadening of the ZPL. Alternatively exciting and ionizing N0 in the lattice results in more distant distribution of N+ ions and a narrowing of the ZPL. The competition between NV− and N0 excitation results in a significant dependence on excitation wavelength and there is also a dependence on the concentration of the NV− and N0 in the samples. The present investigation involves extensive use of low temperature optical spectroscopy to monitor changes to the absorption and emission spectra particularly the widths of the ZPL. The studies lead to a good understanding of the properties of the NV−–N+ pairs in diamond. There is a critical dependence on pair separation. When the NV−–N+ pair separation is large the properties are as for single sites and a high degree of optically induced spin polarization is attainable. When the separation decreases the emission is reduced, the lifetime shortened and the spin polarization downgraded. With separations of <12 A0 there is even no emission. The deterioration occurs as a consequence of electron tunneling in the excited state from NV– to N+ and an optical cycle that involves NV0. The number of pairs with the smaller separations and poorer properties will increase with the number of nitrogen impurities and it follows that the degree of spin polarization that can be achieved for an ensemble of NV− in 1b diamond will be determined and limited by the concentration of single substitutional nitrogen. The information will be invaluable for obtaining optimal conditions when ensembles of NV− are required. As well as extensive measurements of the NV− optical ZPL observations of Stark effects associated with the infrared line at 1042 nm and the optically detected magnetic resonance at 2.87 GHz are also reported. [ABSTRACT FROM AUTHOR]

A theory of a thermally induced single-electron ‘shuttling’ instability in a magnetic nano-mechanical device subject to an external magnetic field is presented in the Coulomb blockade regime of electron transport. The model magnetic shuttle device considered comprises a movable metallic grain suspended between two magnetic leads, which are kept at different temperatures and assumed to be fully spin-polarized with anti-parallel magnetizations. For a given temperature difference shuttling is found to occur for a region of external magnetic fields between a lower and an upper critical field strength, which separate the shuttling regime from normal small-amplitude ‘vibronic’ regimes. We find that (i) the upper critical magnetic field saturates to a constant value in the high temperature limit and that the shuttle instability domain expands with a decrease of the temperature; (ii) the lower critical magnetic field depends not only on the temperature-independent phenomenological friction coefficient used in the model but also on intrinsic friction (which vanishes in the high temperature limit) caused by magnetic exchange forces and electron tunneling between the quantum dot and the leads. The feasibility of using thermally driven magnetic shuttle systems to harvest thermal breakdown phenomena is discussed. [ABSTRACT FROM AUTHOR]

We present a scheme for cooling a vibrational mode of a magnetic molecular nanojunction by a spin-polarized charge current upon exploiting the interaction between its magnetic moment and the vibration. The spin-polarized charge current polarizes the magnetic moment of the nanoisland, thereby lowering its energy. A small but finite coupling between the vibration and the magnetic moment permits a direct exchange of energy such that vibrational energy can be transferred into the magnetic state. For positive bias voltages, this generates an effective cooling of the molecular vibrational mode. We determine parameter regimes for the cooling of the vibration to be optimal. Although the flowing charge current inevitably heats up the vibrational mode via Ohmic energy losses, we show that due to the magnetomechanical coupling, the vibrational energy (i.e, the effective phonon temperature) can be lowered below 50% of its initial value, when the two leads are polarized anti-parallel. In contrast to the cooling effect for positive bias voltages, net heating of the vibrational mode occurs for negative bias voltages. The cooling effect is enhanced for a stronger anti-parallel magnetic polarization of the leads, while the heating is stronger for a larger parallel polarization. Yet, dynamical cooling is also possible with parallel lead alignments when the two tunneling barriers are asymmetric. [ABSTRACT FROM AUTHOR]

We present a quantitative, systematic study of the polarization of the Zeeman magnetic sublevels of the NV-defect in diamond as a function of magnetic field alignment relative to the NV-defect axis. The orientation dependence of NV-polarization in the lab frame is accounted for by a Wigner rotation of a constant defect frame polarization. We also find that the NV-defect level polarizations vary with the P1 defect concentration, and that the polarization of the ms = 0 state with optical pumping decreases from 46% to 36% in samples as P1 concentrations vary from 20 ppm to 100 ppm, respectively. [ABSTRACT FROM AUTHOR]

Many researchers have reported on spin filters using linear Rashba spin–orbit interactions (SOI). However, spin filters using square and cubic Rashba SOIs have not yet been reported. We consider that this is because the Aharonov–Casher (AC) phases acquired under square and cubic Rashba SOIs are ambiguous. In this study, we try to derive the AC phases acquired under square and cubic Rashba SOIs from the viewpoint of non-Abelian SU(2) gauge theory. These AC phases can be derived successfully from the non-Abelian SU(2) gauge theory without the completing square methods. Using the results, we investigate the spin filtering in a double quantum dot (QD) Aharonov–Bohm (AB) ring under linear, square, and cubic Rashba SOIs. This AB ring consists of elongated QDs and quasi-one-dimensional quantum nanowires under an external magnetic field. The spin transport is investigated from the left nanowire to the right nanowire in the above structure within the tight-binding approximation. In particular, we focus on the difference of spin filtering among linear, square, and cubic Rashba SOIs. The calculation is performed for the spin polarization by changing the penetrating magnetic flux for the AB ring subject to linear, square, and cubic Rashba SOIs. It is found that perfect spin filtering is achieved for all of the Rashba SOIs. This result indicates that this AB ring under general Rashba SOIs can be a promising device for spin current generation. Moreover, the AB rings under general Rashba SOIs behave in totally different ways in response to penetrating magnetic flux, which is attributed to linear, square, and cubic behaviors in the in-plane momentum. This result enables us to make a clear distinction between linear, square, and cubic Rashba SOIs according to the peak position of the perfect spin filtering. [ABSTRACT FROM AUTHOR]