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We investigate a novel way to manipulate spin transport properties in two-terminal zigzag graphene nanoribbons with a square-shaped and a triangular-shaped antidots in presence of Rashba spin-orbit coupling. The geometric structure of the antidot shows interesting feature in the spintronic properties of ZGNR. The square-shaped antidote can generate only the y-component of the spin-polarized transmission coefficient, while the triangular-shaped antidote is able to generate all the three components (Px, Py, Pz) of the spin-polarized transmission coefficient. Our results can be generalized in different topological systems and may be tested experimentally.We investigate a novel way to manipulate spin transport properties in two-terminal zigzag graphene nanoribbons with a square-shaped and a triangular-shaped antidots in presence of Rashba spin-orbit coupling. The geometric structure of the antidot shows interesting feature in the spintronic properties of ZGNR. The square-shaped antidote can generate only the y-component of the spin-polarized transmission coefficient, while the triangular-shaped antidote is able to generate all the three components (Px, Py, Pz) of the spin-polarized transmission coefficient. Our results can be generalized in different topological systems and may be tested experimentally.

We consider a double quantum dot in the Kondo regime, coupled to ferromagnetic electrodes in a parallel magnetization configuration, and investigate the influence of the leads’ spin polarization on the Kondo temperature. We perform a second order analytical scaling analysis and compare the results to numerical renormalization group (NRG) simulations. Under certain conditions, a crossover from the orbital and spin SU(4) to an orbital SU(2) Kondo effect is observed as the polarization is varied.

Electron acceleration by ponderomotive force of an intense circularly polarized laser pulse in high density magnetized quantum plasma with two different spin states embedded in external static magnetic field. The basic mechanism involves electron acceleration by axial gradient in the ponderomotive potential of laser. The effects of Bohm potential, fermi pressure and intrinsic spin of electron have been taken into account. A simple solution for ponderomotive electron acceleration has been established and effect of spin polarization is analyzed.

We study the effect of an external magnetic field and electron-phonon interaction on the quantum transport through a molecular electronic device which consists of a strongly interacting quantum dot coupled to metallic leads with tunnel barriers. We model the system by a single-level symmetric Anderson-Holstein model which is solved by using Spectral density approximation method at finite temperature. We use a modified Gaussian ansatz for the spectral function to calculate the charge current and Spin Polarization.We study the effect of an external magnetic field and electron-phonon interaction on the quantum transport through a molecular electronic device which consists of a strongly interacting quantum dot coupled to metallic leads with tunnel barriers. We model the system by a single-level symmetric Anderson-Holstein model which is solved by using Spectral density approximation method at finite temperature. We use a modified Gaussian ansatz for the spectral function to calculate the charge current and Spin Polarization.

TaAs is an ideal Weyl semi-metal consisting of conducting surface states composed of massless Weyl fermions. We have investigated the effects of Nb doping in bulk TaAs. For TaAs/Au and TaAs/Ag interfaces, we have observed huge hole doping to the TaAs system. In addition, the introduced carriers impart a large spin polarization within otherwise non-spin-polarized TaAs.

Using the Quasiparticle Phonon Nuclear Model (QPNM) and taking into account the spin-spin interaction the effects of the spin polarization on the intrinsic magnetic moments (gK) of 153-155Eu isotopes have been studied. Our calculations indicated that because of the spin polarization, the spin gyromagnetic factors (gs) of the nucleons in the nucleus reduce noticeable from its free nucleon value and the spin-spin interactions play an important role in the renormalization (gseff.) of the gs factors. A very good reproduction of the phenomenological quenching of gs factor from its free values (gseff≅0.6−0.7gsfree) is obtained. The calculated values of effective gseff and gK are also in fair agreementwith the experiment data.

We have studied spin dependent electron momentum density in CoGa0.3Fe1.7O4 at 300 K using magnetic Compton spectroscopy. It is observed that major contribution to total spin moment mainly arises from Co ions while itinerant electrons show negative polarization. Orbital contribution has been deduced by comparing the magnetic Compton spectroscopy with the magnetization data. It is revealed that the anisotropy in magnetization in the system increases with the Ga doping.

In this paper, I have presented the spin-dependent momentum density of ferromagnetic dysprosium using spin polarized relativistic Korringa-Kohn-Rostoker method. A fully relativistic approach has been used to determine the magnetic Compton profile. The density of state in term of majority-spin and minority-spin of Dy also calculated using SPR-KKR. The magnetic Compton profile discussed in term of 4f and diffused electrons.

In this article we propose a simple mechanism through which elementary excitations in spin ice, namely magnetic monopoles, lead to spontaneous macroscopic electric polarization through breaking of space inversion symmetry in the spin configuration. We show either the direction or the magnitude of associated electric polarization vector can be conserved in hopping, but both cannot be simultaneous constant of motion, while magnetic charge is constant throughout its movement. A plausible explanation for abnormally large time scale of relaxation for some monopoles reported by Giblin is also demonstrated.

Full potential approach has been employed to tune Fermi level in Co2MnSn1−xSbx (x = 0, 0.25, 0.5, 0.75, 1) Heulser alloys for enhancement of spin polarization and finding signature of half metallicity. Present density functional theory (DFT) based calculation indicates that stoichoimetric Heusler alloy, Co2MnSn is not a half-metallic ferromagnet but the doping of Sb in it results in the shifting of EF in well-defined energy gap which leads the 100% spin polarization in the resultant alloys. The magnetism in present alloys is governed by localized moment on Mn atom mainly. The tuning of half-metallicity using doping can be proved as an ideal technique to search the new materials which can accomplish the need of spintronics.

In this study, we show the modification of the equation of motion of the electronic spin, which is derived by the quantum electron spin vorticity principle, by the effect of the electron electric dipole moment (EDM). To investigate the new contribution to spin torque by EDM, using first principle calculations, we visualize distributions of the local spin angular momentum density and local spin torque density of the YbF molecule on which the static electric field and magnetic field are applied at t = 0.

We have performed numerical ray-tracing Monte-Carlo-simulations of incoherent dynamic neutron scattering experiments. We intend to optimize the efficiency of incoherent measurements depending on the fraction of neutrons scattered without and with spin flip at the sample. In addition to conventional spin echo, we have numerically and experimentally studied oscillating intensity techniques. The results point out the advantages of these different spin echo variants and are an important prerequisite for neutron resonance spin echo instruments like RESEDA (FRM II, Munich), to choose the most efficient technique depending on the scattering vector range and the properties of the sample system under study.

In the ballistic regime where kBTτ / ħ ≥1, the temperature dependence of the metallic conductivity in a two-dimensional hole system of gallium arsenide, is found to change non-monotonically with the degree of spin polarization. In particular, it fades away just before the onset of complete spin polarization, but reappears again in the fully spin-polarized state, being, however, suppressed relative to the zero magnetic field case. The analysis of the degree of suppression can distinguish between screening and interaction-based theories. We show that in a fully polarized spin state, the effects of disorder are dominant and approach a strong localization regime, which is contrary to the behavior of 2D electron systems in a weakly disordered unpolarized state. It was found that the elastic relaxation time correction, depending on the temperature, changed significantly with the degree of spin polarization, to reach a minimum just below the start of the spin-polarized integer, where the conductivity is practically independent of temperature.

The spin torque of the electron is studied in relation to the electric dipole moment (EDM) of the electron. The spin dynamics is known to be given by the spin torque and the zeta force in quantum field theory. The effect of the EDM on the torque of the spin brings a new term in the equation of motion of the spin. We study this effect for a solution of the Dirac equation with electromagnetic field.

We discuss about quantum measurement of a single spin in a superconducting RF resonator, where amplification of coherence of the spin is enabled by transferring its coherence to the harmonic oscillator in an non-coherent state with high energy level. This quantum amplification allows that a single spin can induce macroscopic current to permits observation of a single spin state in the number and phase uncertainty relation.

We study the spin transport in a quasi-one-dimensional channel defined in a two-dimensional electron gas. The combined action of geometrical confinement and the spin precession is analyzed. We demonstrate that for certain orientations of the in-plane magnetic field and for specific range of its magnitude the spin polarization exhibits a strong decrease referred to as ballistic spin resonance (BSR). The phenomenon is due to the commensuration of the Zeeman and inter-subband energy splitting. We show that the BSR requires a finite spin-orbit (SO) interaction although the condition for the BSR onset is independent on SO coupling.

SpectrRelax is an application for analysis and fitting of absorption and emission Mossbauer spectra. It includes a large selection of static and relaxation spectrum models, and allows fitting and searching for optimal model parameters. Recently, we have added new models for Mossbauer spectra of nuclides in spatial spin modulated structures. In these structures, spin density or direction changes in a periodic way along a single direction, and this wave is incommensurate with the underlying lattice. The models include Spin/Charge density wave, where the shape of this wave is represented as a sum of odd harmonics, Anharmonic spin modulation where the spin direction has a cycloidal type modulation, and a Spiral-like spin structure, in which magnetic moments rotate in a plane perpendicular to the wave propagation vector, forming a spiral.

We performed the resistively-detected nuclear magnetic resonance (RDNMR) to study the electron spin polarization in the non-equilibrium quantum Hall regime. By measuring the Knight shift, we derive source-drain bias voltage dependence of the electron spin polarization in quantum wires. The electron spin polarization shows minimum value around the threshold voltage of the dynamic nuclear polarization.

We analyze an effect of a bound impurity state located at a tunnel distance from a quantum well (QW). The study is focused on the resonance case when the bound state energy lies within the continuum of the QW states. Using the developed theory we calculate spin polarization of 2D holes induced by paramagnetic (Mn) delta-layer in the vicinity of the QW and indirect exchange interaction between two impurities located at a tunnel distance from electron gas.

We performed spin-resolved photoluminescence measurements on Ge/SiGe multiple quantum wells with different well thickness and using different exciting power densities. The polarization of the direct emission strongly depends on the relative weight of electrons photoexcited from the light and the heavy hole subbands. The study of the polarization as a function of the exciting power highlights the role of the carrier-carrier interactions in determining spin depolarization. © 2013 AIP Publishing LLC.

We report a theoretical study on the spin-resolved pair-correlation functions gσσ′(r) of a two-dimensional electron gas having arbitrary spin polarization ζ by including the dynamics of exchange-correlations within the dynamical self-consistent mean-field theory of Hasegawa and Shimizu. The calculated g↑↑(r), g↓↓(r) and g↑↓(r) exhibit a nice agreement with the recent quantum Monte Carlo simulation data of Gori-Giorgi et al. However, the agreement for the minority spin correlation function g↓↓(r) decreases with increase in ζ and/or decrease in electron density. Nevertheless, the spin-summed correlation function remains close to the simulation data.

The doping density dependence of the electron spin lifetime in n-type bulk GaN is investigated up to the highly degenerate regime by time-resolved Kerr-rotation spectroscopy. We find a non-monotonic doping density dependence with maximum spin lifetimes at the onset of degeneracy. The reduction of spin lifetimes in the degenerate regime shows a weak τs∝nD−2/3 density dependence, in full agreement with Dyakonov-Perel theory.

In a superconductor-normal-superconductor (SNS) structure, the effect of transverse current across the normal part on the transport through Andreev bound states (ABSs) has been examined. Here a ballistic InAs two-dimensional electron system (2DES) is used as the N-layer to form ABSs. At the same time the 2DES has strong spin-orbit interaction, hence there should emerge the spin-Hall effect associated with the transverse current. We have observed strong reduction of characteristic oscillation in the conductance versus bias voltage, which may be attributed to spin polarization due to the spin-Hall effect.

We apply the principles of Optical Orientation to measure by Mott polarimetry the spin polarization of electrons photoemitted from different group-IV heterostructures. The maximum measured spin polarization, obtained from a Ge/Si0.31Ge0.69 strained film, undoubtedly exceeds the maximum value of 50% attainable in bulk structures. The explanation we give for this result lies in the enhanced band orbital mixing between light hole and split-off valence bands as a consequence of the compressive strain experienced by the thin Ge layer.

Magnetic Compton scattering (MCS) is an ideal technique for the study of magnetic properties of ferro/ferrimagnetic materials because this method reveals the spin-polarized electron momentum density and yields the absolute and site dependent spin moments. The quantity measured in the MCS, so called magnetic Compton profile, is defined as the difference in the one-dimensional projection of the spin-polarized electron momentum density for majority and minority spin bands. In MCS, the Doppler broadening of the scattered radiation provides information on the correlation between the spin moment and the spin-polarized electron states of the valence electrons. It can also distinguish the spin polarization of itinerant electrons, because their momentum is narrow around the center of the profile. In this paper, temperature and field dependent spin momentum densities in Zn doped Ni ferrite namely, Ni1−xZnxFe2O4(x = 0.0,0.1,0.2), hole doped manganites like La0.7Ca0.3Mn1−xAlxO3(x = 0,0.02and0.06) and half Heusler all...

We have investigated the possibility that the coherence length of spatially oscillating electron-spin polarization is improved in dilute magnetic semiconductors. In usual nonmagnetic quantum wells, the spin polarization of the electrons injected from a ferromagnetic source electrode oscillates spatially because of the spin precession due to spin-orbit effective magnetic fields, i.e., the Rashba and Dresselhaus fields. However, the polarization is damped within an oscillation period by the D’yakonov-Perel’ spin relaxation. In paramagnetic dilute magnetic semiconductors, impurity spin polarization is induced under the electron-spin polarization, and this impurity polarization influences the electron-spin precession and possibly improves the spatial electron-spin coherence. The validity of this effect is demonstrated by a numerical simulation for a CdMnTe quantum well.

We report a study of electron spin resonance (ESR) in a perpendicular magnetic field in n-type narrow-gap quantum well (QW) heterostructures. Using the Hartree-Fock approximation, based on the 8×8 k⋅p Hamiltonian, the many-body corrections to the ESR energy are found to be nonzero in symmetric and asymmetric narrow-gap QWs. We demonstrate a significant enhancement of the ESR energy in asymmetric QWs, induced by the Rashba spin splitting and exchange interaction, as well as the exchange-induced enhancement of the ESR energy in symmetric QWs. The ESR energies estimated for 2DEG in InAs/AlSb QWs are compared with experimental results in weak magnetic fields.

The degree of circular polarization of photoluminescence of (In,Ga)As quantum dots as a function of magnetic field applied perpendicular to the optical axis (Hanle effect) is experimentally studied. The measurements have been performed at various regimes of the optical excitation modulation. The analysis of experimental data has been performed in the framework of a vector model of regular nuclear spin polarization and its fluctuations. The analysis allowed us to evaluate the magnitude of nuclear polarization and its dynamics at the experimental conditions used.

Spin momentum density of Nd has been measured at 6K temperature using magnetic Compton scattering. The individual contribution of different electronic states, in the formation of total spin moment, is deduced from the analysis of magnetic Compton profile. The electron-specific spin moments deduced from the experimental Compton data are compared with the theoretical results obtained from full potential linearized augmented plane wave method and are found to be in good agreement.

We have developed a theory of spin orientation by electric current in 2D semiconductors. It is shown that the spin depends on the relation between the energy and spin relaxation times and can vary by a factor of two for the limiting cases of fast and slow energy relaxation. For symmetrically-doped (110)-grown semiconductor quantum wells the effect of current-induced spin orientation is shown to exist due to random spatial variation of the Rashba spin-orbit splitting. We demonstrate that the spin depends strongly on the correlation length of this random spin-orbit field. We calculate the spin orientation degree in two-dimensional topological insulators. In high electric fields when the “streaming” regime is realized, the spin orientation degree weakly depends on the electric field and can reach values about 5%.

The Polish-German project QUEST aims at studying relativistic quantum spin correlations of the Einstein-Rosen-Podolsky-Bohm type, through measurement of the correlation function and the corresponding probabilities for relativistic electron pairs. The results will be compared to theoretical predictions obtained by us within the framework of relativistic quantum mechanics, based on assumptions regarding the form of the relativistic spin operator. Agreement or divergence will be interpreted in the context of non-uniqueness of the relativistic spin operator in quantum mechanics as well as dependence of the correlation function on the choice of observables representing the spin. Pairs of correlated electrons will originate from the Mo/ller scattering of polarized 15 MeV electrons provided by the superconducting Darmstadt electron linear accelerator S-DALINAC, TU Darmstadt, incident on a Be target. Spin projections will be determined using the Mott polarimetry technique. Measurements (starting 2013) are planned for longitudinal and transverse beam polarizations and different orientations of the beam polarization vector w.r.t. the Mo/ller scattering plane. This is the first project to study relativistic spin correlations for particles with mass.

A form of the transverse magnetic susceptibility of a ferromagnetic spin system with a uniaxial anisotropy energy and an anisotropic exchange interaction, interacting with a phonon reservoir, is derived in the spin-wave approximation in terms of the non-equilibrium thermo-field dynamics (NETFD) using the TCLE method. The transverse magnetic susceptibility for the ferromagnetic system of one-dimensional infinite spins is studied by assuming a damped oscillator model of the phonon reservoir. The higher-order effects in the spin-wave approximation are numerically investigated. It is shown that the higher-order parts cannot be neglected for the spin system of the small magnitude and for the high temperature system, but may be neglected for the spin system of the large magnitude.

In the noncentrosymmetric superconductor, the spin-singlet even-parity superconductivity and the spin-triplet odd-parity superconductivity mix each other, in principle. Due to the antisymmetric spin-orbit coupling term breaking the inversion symmetry, anomalous spin fluctuations remain with characteristic momentum dependences, in addition to usual spin fluctuations. It is shown that among anomalous spin fluctuations, antisymmetric spin fluctuations relating with the Dzyaloshinski-Moriya interaction play a role of mixing between different parity superconductivities, and the anomalous spin fluctuations are constructive for mixed-parity superconductivity to develop the spin-triplet superconducting component.

We report here a theoretical model study of the mutual influence of the spin fluctuations and the superconducting gap in the under-doped region of high-Tc cuprate systems. The system is described by the Kondo exchange model for spin interaction between the conduction and the localised impurity f-electrons besides the Heisenberg interaction among the localised f-electrons. This model is treated within a mean-field approximation and the spin components are expressed in terms of the dynamic electron operators. Further, the superconductivity (SC) in the system is described by BCS type pairing mechanism in the conduction electron. The superconducting gap as well as the spin fluctuation parameters of the conduction and localised electrons are calculated by using Zubarev's Green's function technique and are solved self-consistently. Further the tunneling conductance is reflected in the calculated electron density of states which exhibit two gap structure with prominent gap edges.

In this experiment we show the measurement of electronic spin polarization in bulk GaAs using a sensitive rf coil. The basic idea was to excite the electrons from the valence band to the conduction band using a circularly polarized laser. Due to the strong spin orbit coupling in the valence band, a part of the angular momentum of the circularly polarized light is transferred to the electron which allows the excited electron to be spin polarized to certain degree of efficiency, for e.g. 50% for GaAs. The spin of the excited electron decays with a lifetime of about 50ps at 300K. In steady state, for a pump intensity of 100mW at 850nm, a spin polarization density of ∼107 can be achieved in GaAs. These polarized electrons produces a weak magnetization, which was modulated at a frequency of ∼1.8MHz. This generates a varying magnetic field which was detected by a sensitive rf coil of Q-factor ∼33.

Nonlinear magnetosonic waves in degenerate plasmas are discussed by using the spin-1/2 quantum magnetohydrodynamics model. Spin effects are incorporated via spin force and macroscopic spin magnetization current. Using both the reductive perturbation and Sagdeev potential techniques to derive the nonlinear evolution equations. In the limited amplitude a Kadomstev-Petviashvili equation and in arbitrary amplitude an energy integral equation involving Sagdeev potential are derived. The effects of electron spin magnetization, quantum diffraction and plasma statistic (temperature degeneracy) are discussed on the profile of solitons. The importance of the work relevant to compact astrophysical bodies is pointed out.

We present models for the nonlinear interaction between a relativistically strong electromagnetic wave and a quantum plasma. The electron dynamics is modeled using collective nonlinear Schrodinger, Klein-Gordon, and Dirac models, which are coupled nonlinearly with the Maxwell equations for the electromagnetic field. We consider the nonlinear propagation of electromagnetic waves, leading to self-induced transparency, as well as parametric instabilities involving Raman and modulational instabilities, and the acceleration of electrons by electrostatic fields and wakes behind short laser pulses. Spin effects lead to frequency upor downshifts depending on the spin polarization of the plasma and the polarization of the electromagnetic wave. The applications include dense astrophysical bodies and free electron lasers in the quantum regime, where relativistic and quantum effects must be taken into account on an equal footing.

The role of spin-orbit interaction has been exploited to construct an emergent gauge theory in solids. It has been shown that the charge and spin currents in such a solid form a SU(2)×U(1) gauge theory. The lack of gauge symmetry in the SU(2) sector and as a consequence, the non-conservation of spin is spelled out. The phenomenon of spin motive force and spin Hall effect is discussed. The importance of such force in the mesoscopic transport as well as Aharonov-Casher effect is outlined. It is shown that the spin currents in such a theory become the source of electric field.

The spin dependent momentum densities in Ni2MnSn Heusler alloy have been measured at 10 and 300 K using magnetic Compton scattering. For these measurements, we have used 182.79 keV circularly polarized synchrotron radiation at SPring8, Japan. Spin dependent electron momentum densities are analyzed in terms of Mn 3d, Ni 3d and itinerant electrons to calculate their role in formation of net spin moment. Magnetic moments at different sites of constituent atoms have also been compared with the present full potential linearised augmented plane wave calculations and other available data.

Spin currents induced by the spin pumping effect in the presence of Rashba spin‐orbit interaction are studied theoretically. Results indicate that the spin‐orbit interaction induces an effective field which enables us to handle spin currents.

A high degree of spin polarization for the neutral exciton in individual InAs quantum dots, without any external magnetic field applied, is demonstrated. The polarization mechanism is shown to be due to the difference in capture time into the QD for the electrons and holes after photo excitation in the wetting layer. This leads to optical pumping of the QD nuclei by spin polarized electrons and hence suppression of the anisotropic electron—hole exchange interaction.

Microscopy of electron spin states in edge channels are performed by using nuclear spin polarization as a sensitive local probe in the integer quantum Hall regime of the filling factor νbulk = 2. The nuclear polarization situated within the compressible region of 1

We introduce the quantum theory of the electron spin decoherence in a nuclear spin bath and the dynamical decoupling approach for protecting the electron spin coherence. These theories are applied to various solid‐state systems, such as radical spins in molecular crystals and NV centers in diamond.

Spin momentum density of Co2MnO4 has been measured at 10 K using magnetic Compton spectrometer at SPring‐8, Japan. Magnetic Compton profile has also been analyzed to determine the spin moment at different sites of the constituent atoms. It is observed that the Co 3d electrons are coupled antiferromagnetically with Mn 3d electrons. The total magnetic moment of Co2MnO4 is dominated by Mn 3d site. The Compton profile based spin moment at 10 K when compared with the magnetization data (using vibrating sample magnetometer) shows small contribution of orbital moment (0.06±0.02 μB).

We have investigated magnetic properties of semi Heusler compound NiCrS to search the new candidate showing half‐metallic ferromagnetism (HMF) using full potential linearized augmented plane wave (FPLAPW) method within generalized gradient approximation (GGA) formalism for exchange and correlation effects. We predict that this compound is a nearly half‐metallic (HM) ferromagnet with high degree of spin polarization at Fermi level (EF). The total spin magnetic moment is in good agreement with Slater‐Pauling (SP) rule and is dominated by Cr atom.

Spin is a quantum property of electrons. For spin‐based quantum information technology, preparation and read‐out of the electron spin state should be spin coherent. We demonstrate that the polarization coherence of light can be transferred to the spin coherence of electrons in a semiconductor quantum nanostructure, and the prepared coherence of the electron spin can also be read out with light by the developed tomographic Kerr rotation method. We also demonstrate that a single photon is efficiently converted (∼27%) into a single electron trapped in a gate‐defined quantum dot, where the g‐factor of electrons is tuned to zero, and the charge state is detected with an adjacent quantum point contact without destructing the spin state. We further demonstrate that the spin coherence of a single electron trapped in one of double quantum dots is electrically manipulated with a microwave applied to the gate and read out via the Pauli spin blockade phenomenon. All of these functions are needed to build all semicond...

We report a theoretical study of the spin‐resolved pair‐correlation functions gσσ′(r) of the two‐dimensional electron gas having arbitrary spin polarization ζ. The electron correlations are treated beyond the random‐phase approximation within the self‐consistent mean‐field theory of Singwi et al. The calculated g↑↑(r) and g↑↓(r) exhibit a nice agreement with the recent quantum Monte Carlo simulation data of Gori‐Giorgi et al. However, the quality of the minority spin correlation function g↓↓(r) is not that good; rather it decreases further with increasing ζ and/or decreasing electron density. Nevertheless, the spin‐summed correlation function remains close to the simulation data.

We measure the spin polarization (P) of two‐dimensional electron gases confined to an InSb quantum well using parallel and tilted magnetic fields. The nonlinear field dependence of P is prominent, leading to a direct deduction of the spin susceptibility (χs) over a wide range of P from 0.07 to 1. χs is found to increase nonlinearly with P and exceed χgm ∝ m*g* (where m* and g* are the effective mass and g factor) as commonly used in experiments. We show that χs and χgm obey a square law χs/χ0 = (χgm/χ0)2, where χ0 is the paramagnetic spin susceptibility.

This experiment shows the measurement of electronic spin polarization in bulk semiconductors using a sensitive rf coil. The basic idea is to excite the electrons from the valence band to the conduction band using a circularly polarized laser. Due to the strong spin orbit coupling in the valence band, a part of the angular momentum of the light is transferred to the electron which allows them to be spin polarized to certain degree of efficiency, for e.g. 50% for GaAs. The spins decay with a lifetime of about 50ps at 300K. In steady state, for a pump power of 100mW at 850nm, total number of spin polarized electrons ∼107 can be achieved in GaAs. These polarized electrons produce a weak magnetization which was modulated at a frequency of ∼2MHz. The time varying magnetic field generated was then detected by a sensitive tuned rf coil of Q‐factor ∼36.

Pure spin currents, which carry information via spins in lieu of charges, are a key element in spintronics and signify the quantum spin Hall effect. However, they are hardly traceable as they bear neither net magnetization nor net charge currents, notwithstanding many “smoking‐gun” evidences. We show that a pure spin current has measurable second‐order nonlinear optical effects by symmetry analysis and microscopic calculations. These findings may be exploited for directly “seeing” spin currents in real‐time and real‐space with standard nonlinear optical spectroscopy.