Spin Coulomb Drag Research Articles

INFLUENCE OF THE GAUGE FIELD ON TRANSPORT PHENOMENA IN CONDUCTIVE INHOMOGENEOUS MAGNETIC STRUCTURES

The influence of the gauge ("accompanying"), spin-dependent electric field and force induced magnetization dynamics of conducting inhomogeneous magnetic structures, on transport phenomena. It is shown that the transport phenomena, associated with the manifestation of a spin-dependent electric field, lead to the effect of spin Coulomb drag of carriers charge.

Exchange and correlation effects on spin Coulomb drag in a spin-polarized quasi-one-dimensional electron gas

In this paper, we study the spin Coulomb drag (SCD) effect in a spin-polarized quasi-one-dimensional electron gas (Q1DEG) by including the exchange-correlation effects within the self-consistent mean-field approximation of Singwi, Tosi, Land, and Sjölander (the STLS theory). Numerical results for the spin drag rate [Formula: see text] are presented over a wide range of temperature T, some selected values of electron number density [Formula: see text] and spin-polarization. We note that for unpolarized Q1DEG, [Formula: see text] is maximum and then decreases with increase in spin-polarization at each T and/or [Formula: see text]. As an important finding, we report that for a set of critical system parameters at which a long-wavelength spin-density-wave (SDW) instability has been recently reported to occur in a Q1DEG, the drag intensity function attains maxima and [Formula: see text] increases abruptly. However, the random-phase approximation (RPA) underestimates [Formula: see text] in comparison to the STLS theory over a broad range of T and the difference becomes quite appreciable in strongly correlated regime (sufficiently low T and high [Formula: see text]). In addition, we report for the first time the spin-plasmon dispersion of spin-polarized Q1DEG and find that the increase in degree of spin-polarization causes the spectrum to reduce in energy significantly. Besides, the spin-plasmon modes at finite spin-polarization show a consistent blue shift with rise in T and/or [Formula: see text], and the RPA largely overestimates them.

Fermi surface versus Fermi sea contributions to intrinsic anomalous and spin Hall effects of multiorbital metals in the presence of Coulomb interaction and spin-Coulomb drag

Anomalous Hall effect (AHE) and spin Hall effect (SHE) are fundamental phenomena, and their potential for application is great. However, we understand the interaction effects unsatisfactorily, and should have clarified issues about the roles of the Fermi sea term and Fermi surface term of the conductivity of the intrinsic AHE or SHE of an interacting multiorbital metal and about the effects of spin-Coulomb drag on the intrinsic SHE. Here we resolve the first issue and provide the first step about the second issue by developing a general formalism in the linear response theory with appropriate approximations and using analytic arguments. The most striking result is that even without impurities the Fermi surface term, a non-Berry-curvature term, plays dominant roles at high or slightly low temperatures. In particular, this Fermi surface term causes the temperature dependence of the dc anomalous Hall or spin Hall conductivity due to the interaction-induced quasiparticle damping and the correction of the dc spin Hall conductivity due to the spin-Coulomb drag. Those results revise our understanding of the intrinsic AHE and SHE. We also find that the differences between the dc anomalous Hall and longitudinal conductivities arise from the difference in the dominant multiband excitations. This not only explains why the Fermi sea term such as the Berry-curvature term becomes important in clean and low-temperature case only for interband transports but also provides the useful principles on treating the electron-electron interaction in an interacting multiorbital metal for general formalism of transport coefficients. Several correspondences between our results and experiments are finally discussed.

Low-temperature spin coulomb drag in a two-dimensional electron gas

The phenomenon of low-temperature spin Coulomb drag in a two-dimensional electron gas is investigated. The spin transresistivity coefficient is essentially enhanced in the diffusive regime, as compared to conventional predictions. The origin of this enhancement is the quantum coherence of spin-up and spin-down electrons propagating in the same random impurity potential and coupled via the Coulomb interaction. A comprehensive analysis of spin and interlayer Coulomb drag effects is presented.

Nonlocal formulation of spin Coulomb drag

The spin Coulomb drag (SCD) effect occurs in materials and devices where charged carriers with different spins exchange momentum via Coulomb scattering. This causes frictional forces between spin-dependent currents that lead to intrinsic dissipation, which may limit spintronics applications. A nonlocal formulation of SCD is developed which is valid for strongly inhomogeneous systems such as nanoscale spintronics devices. This nonlocal formulation of SCD is successfully applied to linewidths of intersubband spin plasmons in semiconductor quantum wells, where experiments have shown that the local approximation fails.

Spin polarization effect on spin Coulomb drag in a two-dimensional electron system

We study the effect of spin polarization on spin-drag transresistivity in a two-dimensional (2D) electron gas at temperature T beyond the random phase approximation (RPA). We make use of spin resolved static local field factors for 2D spin polarized electron gas to take into account the many-body electronic correlation beyond the RPA. The main result of our work is that the reduction in spin Coulomb drag (SCD), due to the spin polarization of the system, is significantly compensated by the inclusion of the many-body local field corrections. We also calculate the temperature behavior of spin diffusion constant based on SCD theory for a spin polarized electron system.

Critical exponents for the spin Coulomb drag in the Hubbard chain

The spin Coulomb drag is the decay of the spin current in a metal as a consequence of the Coulomb interaction between up- and down-spin carriers. We calculate the critical exponents of the resistivity for up- and down-spin electrons and the transresistivity for the spin-polarized Hubbard chain with nonmagnetic impurities within the Kubo formalism using the Bethe Ansatz solution and conformal invariance. Due to the Luttinger liquid properties the temperature dependence of the transport correlation functions follows power laws of T with nonuniversal exponents.

Spin Coulomb drag in the Hubbard chain

The spin Coulomb drag is the decay of the spin current in a metal as a consequence of the Coulomb interaction between up- and down-spin carriers. This interaction reduces the spin current but does not change the spin-polarization. We calculate the critical exponents of the resistivity for up- and down-spin electrons and the transresistivity for the spin-polarized Hubbard chain with nonmagnetic impurities within the Kubo formalism using the Bethe ansatz solution and conformal invariance. Due to the Luttinger liquid properties the temperature dependence of the transport correlation functions follow power laws of $T$ with nonuniversal exponents.

Spin Coulomb Drag in a One-Dimensional Spin-Polarized Conductor

The spin Coulomb drag is a distinctive feature of spin-polarized transport. The current of majority spins can induce a current of minority spin carriers via the transconductivity. The friction is caused by the Coulomb interaction between up- and down-spin. This interaction reduces the current but does not change the spin-polarization. We calculate the conductivities and the transconductivity for a spin-polarized interacting 1-D electron gas for a lattice without inversion symmetry in the presence of nonmagnetic impurities. Due to the Luttinger liquid properties, the temperature dependence of the transport correlation functions follows power laws of with nonuniversal exponents.

Front Cover (Phys. Status Solidi B 2/2010)

The spin Coulomb drag constitutes an intrinsic source of dissipation for spin currents generated by charged carriers. The effect is due to Coulomb scattering between carriers of opposite spin moving with different velocities, and is of importance in three-, two-, and one-dimensional systems. The spin Coulomb drag has various practical implications for spintronics, playing an important role in the spin injection and drift-diffusion in semiconductors, and in the power loss of spin circuits. It affects spin-optical excitations and contributes to the line width of spin plasmons. The Feature Article by Irene D'Amico and Carsten Ullrich, which starts on page 235, provides an overview of the topic.

Coulomb interactions and spin transport in semiconductors: The spin Coulomb drag effect

The spin Coulomb drag (SCD) constitutes an intrinsic source of dissipation for spin currents generated by charged carriers. We discuss the physical origin of the effect, which is due to Coulomb scattering between carriers of opposite spin moving with different velocities, distinguishing between three-, two-, and one-dimensional systems. An overview is given of the various practical implications of the SCD effect for spintronics, where it plays an important role in spin injection and drift-diffusion in semiconductors, and in the power loss of spin circuits. The SCD also affects spin-optical excitations and contributes to the linewidth of spin plasmons. We discuss how the effect can be viewed in the context of time-dependent density-functional response theory.

Finite Width and Local Field Corrections to Spin Coulomb Drag in a Quasi-Two-Dimensional Electron Gas

We study the spin Coulomb drag in a quasi-two-dimensional electron gas of finite transverse width, including local field corrections beyond the random phase approximation (RPA). We find that the finite transverse width of the electron gas causes a significant reduction of the spin Coulomb drag. This reduction, however, is largely compensated by the enhancement coming from the inclusion of many-body local field effects beyond the RPA, thereby restoring good agreement with the experimental observations by C. P. Weber et al. [Nature (London) 437, 1330 (2005)].

Exchange and correlation effect on spin Coulomb drag in a quasi-two-dimensional electron system

We investigate the effect of many-body electronic correlations on spin Coulomb drag (SCD) beyond the random phase approximation (RPA). We make use of the fully spin-resolved static and dynamical many-body local field factors of the two-dimensional electron gas (2DEG) to improve the calculations of the particle-hole and plasmon-mediated contributions to the SCD. Also, we incorporate in our calculations the transverse thickness of the quantum well in which the 2DEG resides. In contrast to the conventional charge Coulomb drag, in the SCD the effect of layer thickness is significant even at relatively high temperature and densities. The final outcome of our study is that the enhancement of the spin drag caused by many-body local field effects largely compensates the reduction of the effect coming from the finite well thickness, restoring good agreement with the experimental observations by C.P. Weber et al., Nature 437 (2005) 1330.

Gilbert damping and spin Coulomb drag in a magnetized electron liquid with spin-orbit interaction

We present a microscopic calculation of the Gilbert damping constant for the magnetization of a two-dimensional spin-polarized electron liquid in the presence of intrinsic spin-orbit interaction. First we show that the Gilbert constant can be expressed in terms of the auto-correlation function of the spin-orbit induced torque. Then we specialize to the case of the Rashba spin-orbit interaction and we show that the Gilbert constant in this model is related to the spin-channel conductivity. This allows us to study the Gilbert damping constant in different physical regimes, characterized by different orderings of the relevant energy scales -- spin-orbit coupling, Zeeman coupling, momentum relaxation rate, spin-momentum relaxation rate, spin precession frequency -- and to discuss its behavior in various limits. Particular attention is paid to electron-electron interaction effects,which enter the spin conductivity and hence the Gilbert damping constant via the spin Coulomb drag coefficient.

Intrinsic power loss and damping of optical excitations in spintronic devices

Spin Coulomb drag (SCD) provides an intrinsic source of dissipation for spin currents in metals and semiconductors and thus plays a fundamental role in spintronics. We discuss two aspects of SCD and their practical relevance: the power loss in a generic spintronics device, and the damping of collective spin-density excitations in semiconductor quantum wells. A purely optical quantitative measurement of the SCD effect is suggested, and the role of spin–orbit coupling is discussed.

Coulomb drag and spin drag in the presence of spin-orbit coupling

Employing diagrammatic perturbation theory, we calculate the (charge) Coulomb drag resistivity ${\ensuremath{\rho}}_{\mathrm{D}}$ and spin Coulomb drag resistivity ${\ensuremath{\rho}}_{\ensuremath{\uparrow}\ensuremath{\downarrow}}$ in the presence of Rashba spin-orbit coupling. Analytical expressions for ${\ensuremath{\rho}}_{\mathrm{D}}$ and ${\ensuremath{\rho}}_{\ensuremath{\uparrow}\ensuremath{\downarrow}}$ are derived, and it is found that spin-orbit interaction produces a small enhancement to ${\ensuremath{\rho}}_{\mathrm{D}}$ and ${\ensuremath{\rho}}_{\ensuremath{\uparrow}\ensuremath{\downarrow}}$ for weakly disordered systems (Boltzmann regime) while ${\ensuremath{\rho}}_{\mathrm{D}}$ is unchanged for dirty systems (diffusive regime). This enhancement in the Boltzmann regime is attributed to the enhancement of the nonlinear susceptibility (i.e., current produced through the rectification of the thermal electric potential fluctuations in the passive layer) while the lack of enhancement in the diffusive regime is due to the suppression by disorder.

Dissipation through spin Coulomb drag in electronic spin transport and optical excitations

Spin Coulomb drag (SCD) constitutes an intrinsic source of dissipation for spin currents in metals and semiconductors. We discuss the power loss due to SCD in potential spintronics devices and analyze in detail the associated damping of collective spin-density excitations. It is found that SCD contributes substantially to the linewidth of intersubband spin plasmons in semiconductor quantum wells, which suggests the possibility of a purely optical quantitative measurement of the SCD effect in a parabolic well through inelastic light scattering.

Coulomb corrections to the extrinsic spin-Hall effect of a two-dimensional electron gas

We develop the microscopic theory of the extrinsic spin-Hall conductivity of a two-dimensional electron gas, including skew-scattering, side-jump, and Coulomb interaction effects. We find that while the spin-Hall conductivity connected with the side jump is independent of the strength of electron-electron interactions, the skew-scattering term is reduced by the spin-Coulomb drag, so the total spin current and the total spin-Hall conductivity are reduced for typical experimental mobilities. Further, we predict that in paramagnetic systems the spin-Coulomb drag reduces the spin accumulations in two different ways: (i) directly through the reduction of the skew-scattering contribution, and (ii) indirectly through the reduction of the spin diffusion length. Explicit expressions for the various contributions to the spin-Hall conductivity are obtained using an exactly solvable model of the skew scattering.

Observation of spin Coulomb drag in a two-dimensional electron gas

An electron propagating through a solid carries spin angular momentum in addition to its mass and charge. Of late there has been considerable interest in developing electronic devices based on the transport of spin that offer potential advantages in dissipation, size and speed over charge-based devices. However, these advantages bring with them additional complexity. Because each electron carries a single, fixed value (- e) of charge, the electrical current carried by a gas of electrons is simply proportional to its total momentum. A fundamental consequence is that the charge current is not affected by interactions that conserve total momentum, notably collisions among the electrons themselves. In contrast, the electron's spin along a given spatial direction can take on two values, +/- [planck]/2 (conventionally upward arrow, downward arrow), so that the spin current and momentum need not be proportional. Although the transport of spin polarization is not protected by momentum conservation, it has been widely assumed that, like the charge current, spin current is unaffected by electron-electron (e-e) interactions. Here we demonstrate experimentally not only that this assumption is invalid, but also that over a broad range of temperature and electron density, the flow of spin polarization in a two-dimensional gas of electrons is controlled by the rate of e-e collisions.

Observing the spin Coulomb drag in spin-valve devices

The Coulomb interaction between electrons of opposite spin orientations in a metal or in a doped semiconductor results in a negative off-diagonal component of the electrical resistivity matrix -- the so-called "spin-drag resistivity". It is generally quite difficult to separate the spin-drag contribution from more conventional mechanisms of resistivity. In this paper I discuss two methods to accomplish this separation in a spin-valve device.