Electric field tunability of nuclear and electronic spin dynamics due to the hyperfine interaction in semiconductor nanostructures

We present formulas for the nuclear and electronic spin relaxation times due to the hyperfine interaction for nanostructed systems and show that the times depend on the square of the local density of electronic states at the nuclear position. A drastic sensitivity (orders of magnitude) of the electronic and nuclear spin coherence times to small electric fields is predicted for both uniformly distributed nuclear spins and delta-doped layers of specific nuclei. This sensitivity is robust to nuclear spin diffusion.     

Effect of electric-field on spin transport and spin current in an organic semiconductor system

We use the two-component drift-diffusion model to study the spin density polarization in an organic semiconductor system under an external electric-field. The spin-dependent electrical-conductivity, the drift spin current and the diffusion spin current in the organic semiconductor are self-consistently derived. It is found that the spin current could be strongly influenced by the spin-dependent electrical-conductivity. When the spin-dependent conductivity varies from 0 to 0.5%, the spin current presents a very pronounced change almost three orders in magnitude. The electric-field could effectively enhance the spin-dependent electrical-conductivity and the spin current. Furthermore, the spin-dependent electrical-conductivity is position sensitive, but its position sensitivity goes down while electric-field is larger than about 1 mV/μm.     

THz-field induced nonlinear transport and dc voltage generation in a semiconductor superlattice due to Bloch oscillations

We report on a theoretical analysis of terahertz (THz-) field induced nonlinear dynamics of electrons in a semiconductor superlattice that are capable to perform Bloch oscillations. Our results suggest that for a strong THz-field a dc voltage should be generated. We have analyzed the real-time dynamics using a balance equation approach to describe the electron transport in a superlattice miniband. Taking account of both Bloch oscillations of electrons in a superlattice miniband and dissipation, we studied the influence of a strong THz-field on currently available superlattices at room temperature. We found that a THz-field can lead to a negative conductance resulting in turn in a THz-field induced dc voltage, and that the voltage per superlattice period should show, for varying amplitue of the THz-field, a form of wisted plateaus with the middle points being with high precision equal to the photon energy divided by the electron charge. We show voltage to the finite voltage state, and that in the finite voltage state dynamic localization of the electrons in a miniband occurs.     

A new mechanism of electromagnetic electron radiation in a medium (spin light)

Based on the method of exact solutions to the quantum equations for the wave functions of particles in external fields and media within the framework of the standard interaction model, the modified Dirac equation for the electron is derived that allows its interaction with the medium to be considered. An exact solution to the equation and energy spectrum of the electron states are determined. In the context of this approach, a new type of electromagnetic radiation-spin light of electron in a neutron medium-is predicted and studied. General expressions for the probability of the process in unit time and for the radiation intensity are derived, and a dependence of the radiation intensity on the electron energy and density of the medium is analyzed. The limiting cases of the process and polarization properties of radiation are investigated. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 66–73, June, 2007.     

Electric dipole spin resonance for heavy holes in quantum dots

We propose and analyze a new method for manipulation of a heavy-hole spin in a quantum dot. Because of spin-orbit coupling between states with different orbital momenta and opposite spin orientations, an applied rf electric field induces transitions between spin-up and spin-down states. This scheme can be used for detection of heavy-hole spin resonance signals, for the control of the spin dynamics in two-dimensional systems, and for determining important parameters of heavy holes such as the effective g factor, mass, spin-orbit coupling constants, spin relaxation, and decoherence times.     

Lifetime-enhanced transport in silicon due to spin and valley blockade

We report the observation of lifetime-enhanced transport (LET) based on perpendicular valleys in silicon by transport spectroscopy measurements of a two-electron system in a silicon transistor. The LET is manifested as a peculiar current step in the stability diagram due to a forbidden transition between an excited state and any of the lower energy states due to perpendicular valley (and spin) configurations, offering an additional current path. By employing a detailed temperature dependence study in combination with a rate equation model, we estimate the lifetime of this particular state to exceed 48 ns. The two-electron spin-valley configurations of all relevant confined quantum states in our device were obtained by a large-scale atomistic tight-binding simulation. The LET acts as a signature of the complicated valley physics in silicon: a feature that becomes increasingly important in silicon quantum devices.     

Terahertz radiation of Bloch oscillators excited by an electromagnetic field in lateral semiconductor superlattices

The action of a strong high-frequency electromagnetic field on a lateral semiconductor superlattice is considered based on the quasi-classical electron transport theory in the self-consistent wave formulation. The theory predicts that a lateral superlattice can emit terahertz radiation wave trains, which are associated with periodic excitation of Bloch oscillations in the superlattice arising because of the development of transient processes in it in a variable self-consistent electric field. The conditions necessary for observing Bloch oscillator radiation were found. The spectral composition of radiation transmitted through the superlattice and the energy efficiency of frequency multiplication related to Bloch oscillator excitation were calculated.     

Vortex viscosity in magnetic superconductors due to radiation of spin waves

In type-II superconductors that contain a lattice of magnetic moments, vortices polarize the magnetic system inducing additional contributions to the vortex mass, vortex viscosity, and vortex-vortex interaction. Extra magnetic viscosity is caused by radiation of spin waves by a moving vortex. Like in the case of Cherenkov radiation, this effect has a characteristic threshold behavior and the resulting vortex viscosity may be comparable to the well-known Bardeen-Stephen contribution. The threshold behavior leads to an anomaly in the current-voltage characteristics, and a drop in dissipation for a current interval that is determined by the magnetic excitation spectrum.     

Heating of electrons in superconductor in the resistive state due to electromagnetic radiation

The effect of heating electrons with respect to phonons in a thin superconducting film driven into the resistive state by the current and the external magnetic field has been observed and investigated. This effect caused by the electromagnetic radiation is manifested in the increased resistance of the film and is not selective over the frequency range from 10¹⁰ to 10¹⁵ Hz. That the effect is frequency independent under the conditions of strong electron scattering caused by static defects is explained by the decisive role of electron -electron collisions in forming the distribution function. The characteristic time of resistance change, obtained experimentally, corresponds to the relaxation time of the order parameter $\text{τ}{}_{\mathrm{\Delta }}$ near the superconducting transition and to the relaxation time of the nonelastic electron-phonon interaction $\text{τ}{}_{\mathrm{<mtext>eph</mtext>}}$ at lower temperatures and in lower magnetic fields.     

Asymmetric transport due to spin injection into a Kondo alloy

Spin injection is found to have a significant effect on the transport properties of the Kondo alloy Cu(Fe). When a spin-polarized electron current flows from Co into Cu(Fe) wires through the Co/Cu(Fe) interface, the resistivity of the Cu(Fe) wire is suppressed near the interface, as distinct from the ordinary logarithmic increase in the resistivity at low temperatures. For the opposite current direction, no significant changes are observed. The asymmetry of the resistivity with respect to the current direction decays with a characteristic length of 1.5+/-0.4 microm at 2.5 K as the distance from the interface is increased. Possible mechanisms for the asymmetry are discussed.     

Recombination radiation of a semiconductor in the field of a strong electromagnetic wave

The spontaneous recombination radiation spectrum of a semiconductor in the external field of an arbitrary polarized laser wave in the saturation state is investigated. Considerable dependence of the electromagnetic energy radiation rate of predetermined frequency upon the polarization type of the exciting field is predicted.     

On the magnetic dipole absorption of electromagnetic radiation by a fine conducting particle

The cross section of absorption of electromagnetic radiation by a fine spherical conducting particle is estimated in terms of the classical kinetic theory of electrical conduction. The mixed diffuse-specular mechanism of charge carrier reflection from the sample boundary is considered. A correlation between the coefficient of specular reflection and the absorption cross section at different temperatures is analyzed.     

A novel mechanism for spin dephasing due to spin-conserving scatterings

A new spin dephasing mechanism is proposed for semiconductors with carrier momentum-dependent transition energies (inhomogeneous broadening) between spin states. In the presence of this inhomogeneous broadening of the spin transitions, spin-conserving (SC) scatterings lead to irreversible spin dephasing in a complete analogy to the optical dephasing of inhomogeneously broadened optical transitions. This phenomenon is demonstrated for the case when the g-factor becomes electron-energy dependent. Received 29 June 2000     

Electron spin precession in the field of an electromagnetic wave

The solution of the Dirac equation for an electron in the field of a plane circularly polarized electromagnetic wave having an arbitrary intensity and a phase velocity v _ph different from the speed of light c is obtained. This solution is shown to describe the previously unknown effect of electron spin precession that exceeds the known precession effects caused by radiative corrections by six and more orders of magnitude and opens new possibilities for control of the polarization of electrons and for realization of various resonance methods associated with the spin precession. The predicted effect is in agreement with symmetry principles; however, it disappears at v _ph=c and is not described by the known Volkov solution.     

Material dependence of spin transport modulated by magnetic barriers in semiconductor nano-wires

We present the properties of ballistic spin transport through magnetic barrier structures in semiconductor nano-wires. The Landauer's approach is adopted to calculation of the transmission probability and the conductance for various host material nano-wires which are different remarkably from each other in effective g-factors. A host material having small effective g-factor is quantized in the conductance and the spin-dependence is disappeared in it. Nevertheless this kind of behavior is broken for the host material having large effective g-factor and the spin-dependent splitting is shown.     

辐射超声速扩散传输产生条件的研究

 利用1维辐射扩散方程的解析理论,在外加辐射源为恒温源的条件下,对能够产生辐射超声速扩散传输的条件进行了研究,可以解析地得出在固定物质密度下能够产生超声速扩散流的参数区域。分析得出：对于一个固定的恒温外源,随着时间的增加,热波波头位置是随时间的平方根增长的,光学厚度正比于波头位置,也是随时间而逐渐增加的;而马赫数是按时间平方根倒数减少的。并推导出在不同密度下恰好产生超声速扩散时,辐射源温度和辐射热波波头位置满足的临界值条件,它们是关于介质密度的函数关系式。最后以SiO₂泡沫为算例,对这些结果的物理图像做了简要的阐述,对它们的应用进行了具体的说明和分析。     

Large spin diffusion length in an amorphous organic semiconductor

We directly measured a spin diffusion length (lambdas) of 13.3 nm in amorphous organic semiconductor (OS) rubrene (C42H28) by spin polarized tunneling. In comparison, no spin-conserved transport has been reported in amorphous Si or Ge. Absence of dangling bond defects can explain the spin transport behavior in amorphous OS. Furthermore, when rubrene barriers were grown on a seed layer, the elastic tunneling characteristics were greatly enhanced. Based on our findings, lambdas in single-crystalline rubrene can be expected to reach even millimeters, showing the potential for organic spintronics development.     

Transmission of electric dipole radiation through an interface

We consider the transmission of electric dipole radiation through an interface between two dielectrics, for the case of a vertical dipole. Energy flows along the field lines of the Poynting vector, and in the optical near field these field lines are curves (as opposed to optical rays). When the radiation passes through the interface into a thicker medium, the field lines bend to the normal (as rays do), but the transmission angle is not related to the angle of incidence. The redirection of the radiation at the interface is determined by the angle dependence of the transmission coefficient. This near-field redistribution is responsible for the far-field angular power pattern. When the transmission medium is thinner than the embedding medium of the dipole, some energy flows back and forth through the interface in an oscillating fashion. In each area where field lines dip below the interface, an optical vortex appears just above the interface. The centers of these vortices are concentric singular circles around the dipole axis.     

A significantly enhanced magnetic moment due to an electric dipole moment

We demonstrate via first-principle calculations based on the density functional theory that the magnetic moment of a helium atom under a given magnetic field has a positive correlation with the electric dipole moment when an external electric field is applied to the system. Our calculation shows that the enhancement of the magnetic moment is significant due to the reduction of the tripletsinglet splitting. We argue that this finding can be generalized to organic molecules, especially to macromol...