Search

Using artificially controlled ferromagnet (FM)–semiconductor (SC) interfaces, we study the decay of the nonlocal spin signals with increasing temperature in SC-based lateral spin-valve devices. When more than five atomic layers of Fe are inserted at the FM/SC interfaces, the temperature-dependent spin injection/detection efficiency (P inj / det ) can be interpreted in terms of the T 3 2 law, meaning a model of the thermally excited spin waves in the FM electrodes. For the FM/SC interfaces with the insufficient insertion of Fe atomic layers, on the other hand, the decay of P inj / det is more rapid than the T 3 2 curve. Using magneto-optical Kerr effect measurements, we find that more than five atomic layers of Fe inserted between FM and SC enable us to enhance the ferromagnetic nature of the FM/SC heterointerfaces. Thus, the ferromagnetism in the ultra-thin FM layer just on top of SC is strongly related to the temperature-dependent nonlocal spin transport in SC-based lateral spin-valve devices. We propose that the sufficient ferromagnetism near the FM/SC interface is essential for high-performance FM–SC hybrid devices above room temperature. [ABSTRACT FROM AUTHOR]

We consider Mn-doped bulk zinc-blende semiconductors described by the 4 × 4 Luttinger Hamiltonian. In these semiconductors, the Mn atom acts as an acceptor providing the system a mobile hole and also acts like a magnetic impurity of spin S = 5 / 2. We obtain exact analytical expressions of the hole mediated Ruderman-Kittel-Kasuya-Yoshida (RKKY) exchange interaction between two Mn 2 + ions. The RKKY interaction of the Luttinger system consists of collinear Heisenberg-like and Ising-like interactions. The characteristic beating patterns appear in the range functions of the RKKY interaction owing to the presence of multiple Fermi wave-vectors of the underlying j = 3 / 2 states. As an application of the analytical form of the range function, from the finite temperature evaluation of the correlation functions, we calculate the contribution of RKKY interaction to the Curie-Weiss temperatures of a particular dilute magnetic semiconductor ZnMnTe where the 4 × 4 Luttinger Hamiltonian is valid. [ABSTRACT FROM AUTHOR]

We studied spin dephasing processes in GaAs/AlGaAs multiple quantum wells (MQWs) grown on a semi-insulating (110)-oriented GaAs substrate using the time-resolved Kerr rotation (TRKR) technique. The TRKR spectra gives the electron g-factor in MQWs, as well as the spin dephasing time (SDT) for electron spins within the sample plane. The electron g-factor shows a strong two-fold anisotropy, while the in-plane SDT remains almost isotropic. The anisotropy of the electron g-factor increases monotonically with the spread of more electron wave functions into the AlGaAs barrier. The two-fold symmetry of the electron g-factor is discussed with a phenomenological model based on spin splitting of energy bands caused by spin-orbit coupling. [ABSTRACT FROM AUTHOR]

Electrical spin-injection across the Fe3O4:Al0.1Ga0.9As interface has been measured. We quantify this effect in an In0.2Ga0.8As:GaAs spin-light emitting diode optical device. The optical polarization signal is maintained from 4.2 up to 200 K without influence of the metal–insulator Verwey transition in the bulk of the Fe3O4 film. An incomplete oxidation at the interface may be detrimental for this device, as it has a similar spin-injection efficiency to that of Fe:Al0.1Ga0.9As. Ambient temperature operation of this device may be possible although the present polarization levels remain too low for practical spintronic applications. We demonstrate the first step in the integration of molecular beam epitaxy-grown magnetic oxides into III–V semiconductor devices. [ABSTRACT FROM AUTHOR]

Double quantum dots (DQDs) hold great promise as building blocks for quantum technology as they allow for two electronic states to coherently couple. Defining QDs with materials rather than using electrostatic gating allows for QDs with a hard-wall confinement potential and more robust charge and spin states. An unresolved problem is how to individually address these QDs, which is necessary for controlling quantum states. We here report the fabrication of DQD devices defined by the conduction band edge offset at the interface of the wurtzite and zinc blende crystal phases of InAs in nanowires. By using sacrificial epitaxial GaSb markers selectively forming on one crystal phase, we are able to precisely align gate electrodes allowing us to probe and control each QD independently. We hence observe textbooklike charge stability diagrams, a discrete energy spectrum, and electron numbers consistent with theoretical estimates and investigate the tunability of the devices, finding that changing the electron number can be used to tune the tunnel barrier as expected by simple band diagram arguments. [ABSTRACT FROM AUTHOR]

Electrical spin injection into and spin extraction from a wide-bandgap semiconductor SiC at room temperature were demonstrated via Schottky junctions. The spin relaxation time of SiC could reach 300 ps, overwhelming that of Si with similar carrier density due to the smaller atomic number. We also found that there existed two channels in SiC/CoFeB Schottky junctions for spin relaxation, one from bulk SiC and the other from interfacial defect states within the barrier whose spin relaxation times were about 1 ns. The bias condition controlled transport channels via bulk or defect states within the barrier and then affected the effective spin relaxation process. Realization of spin injection into SiC shed light on spintronics of wide-bandgap semiconductors such as spin-resolved blue light emitting diodes and high power/temperature spintronics. [ABSTRACT FROM AUTHOR]

Recent spin noise spectroscopy measurements showed at low temperatures unexpected large g-factor fluctuations in highly n-doped bulk GaAs which were attributed to intrinsic g-factor fluctuations due to the stochastic nature of the doping distribution. In this publication, we extend these low temperature magnetic field dependent spin noise measurements from 20 up to 260 K. A global fit of all magnetic field and temperature dependent measurements with just three common fit parameters yields good qualitative agreement with the stochastic doping model taking into account the dominating electron momentum scattering by ionized impurities and electron-plasmon scattering which contribute about equally. The magnetic field dependent Larmor precession of the electron spin yields for the studied doping concentration of [ABSTRACT FROM AUTHOR]

The coherent spin dynamics of carriers in the heterostructures that contain an InGaAs/GaAs quantum well (QW) and an Mn δ layer, which are separated by a narrow GaAs spacer 2-10 nm thick, is comprehensively studied by the magnetooptical Kerr effect method at a picosecond time resolution. The exchange interaction of photoexcited electrons in QW with the ferromagnetic Mn δ layer manifests itself in magnetic-field and temperature dependences of the Larmor precession frequency of electron spins and is found to be very weak (several microelectron volts). Two nonoscillating components related to holes exist apart from an electron contribution to the Kerr signal of polarization plane rotation. At the initial stage, a fast relaxation process, which corresponds to the spin relaxation of free photoexcited holes, is detected in the structures with a wide spacer. The second component is caused by the further spin dephasing of energyrelaxed holes, which are localized at strong QW potential fluctuations in the structures under study. The decay of all contributions to the Kerr signal in time increases substantially when the spacer thickness decreases, which correlates with the enhancement of nonradiative recombination in QW. [ABSTRACT FROM AUTHOR]

We demonstrate strong light-matter coupling in three dimensional terahertz meta-atoms at room temperature. The intersubband transition of semiconductor quantum wells with a parabolic energy potential is strongly coupled to the confined circuital mode of three-dimensional split-ring metal-semiconductor-metal resonators that have an extreme sub-wavelength volume (λ/10). The frequency of these lumped-element resonators is controlled by the size and shape of the external antenna, while the interaction volume remains constant. This allows the resonance frequency to be swept across the intersubband transition and the anti-crossing characteristic of the strong light-matter coupling regime to be observed. The Rabi splitting, which is twice the Rabi frequency (2ΩRabi), amounts to 20% of the bare transition at room temperature, and it increases to 28% at low-temperature. [ABSTRACT FROM AUTHOR]

This article gives an overview on the advance of spin noise spectroscopy (SNS) in semiconductors in the past 8 years from the first measurements in bulk n-GaAs [Oestreich et al., Phys. Rev. Lett. 95, 216603 (2005)] up to the recent achievement of optical detection of the intrinsic spin fluctuations of a single hole confined in an individual self-assembled quantum dot [Dahbashi et al., arXiv:1306.3183 (2013)]. We discuss the general technical implementation of optical SNS and the invaluable profit of the introduction of real-time fast Fourier transform analysis into the data acquisition. By now, the full spin dynamic from the milli- to picosecond timescales can be addressed by SNS and the technique quickly strides ahead to enable real quantum non-demolition measurements in semiconductors. Spin noise spectra recorded in 2005 in bulk n-GaAs with approximately 109 electron spins (Oestreich et al.) and 2013 (Dahbashi et al.) for a single hole spin. The integration time for the latter is more than a factor of 40 shorter due to the significant advances in the measurement technique. [ABSTRACT FROM AUTHOR]

The paper reviews the interplay of Rashba/Dresselhaus spin splittings in various two-dimensional systems made of zinc-blende III-V, wurtzite, and SiGe semiconductors. We discuss the symmetry aspects of the linear and cubic in electron wavevector spin splitting in heterostructures prepared on (001)-, (110)-, (111)-, (113)-, (112)-, and (013)- oriented substrates and address the requirements for suppression of spin relaxation and realization of the persistent spin helix state. In experimental part of the paper, we overview experimental results on the interplay of Rashba/Dresselhaus spin splittings probed by photogalvanic spectroscopy: The method based on the phenomenological equivalence of the linear-in-wavevector spin splitting and several photogalvanic phenomena. [ABSTRACT FROM AUTHOR]

Since the prediction of the spin Hall effect more than 40 years ago, significant progress was made in theoretical description as well as in experimental observation, especially in the last decade. In this article, we present three different concepts and measurement geometries for all-electrical detection of the direct and the inverse spin Hall effect in semiconductors. Based on experiments with n- and p-doped GaAs microstructures, we describe our experimental approaches and methods to experimentally identify the spin Hall effect and compare our results to previous experiments and theoretical considerations. Device geometry for the detection of the direct spin Hall effect. [ABSTRACT FROM AUTHOR]

The CoFe thickness (tCoFe) dependence of spin injection efficiency was investigated for Co2MnSi/CoFe/n-GaAs junctions. The ΔVNL/I value, which is a measure of spin injection efficiency, strongly depended on tCoFe, where ΔVNL is the amplitude of a nonlocal spin-valve signal, and I is an injection current. Importantly, the maximum value of ΔVNL/I for a Co2MnSi/CoFe/n-GaAs junction was one order of magnitude higher than that for a CoFe/n-GaAs junction, indicating that a Co2MnSi electrode works as a highly polarized spin source. No clear spin signal, on the other hand, was observed for a Co2MnSi/n-GaAs junction due to diffusion of Mn atoms into the GaAs channel. Secondary ion mass spectrometry analysis indicated that the CoFe insertion effectively suppressed the diffusion of Mn into GaAs, resulting in improved spin injection properties compared with those for a Co2MnSi/n-GaAs junction. [ABSTRACT FROM AUTHOR]

We propose a method of two-beam spin noise spectroscopy to test the spin transport at equilibrium via analysis of correlations between time-shifted spin fluctuations at different space locations. This method allows one to determine the strength of spin-orbit interaction and spin relaxation time and separate spin noise of conducting electrons from the background noise of localized electrons. We formulate a theory of two-beam spin noise spectroscopy in semiconductor wires with Bychkov-Rashba spin-orbit interaction taking into account several possible spin relaxation channels and finite size of laser beams. Our theory predicts a peak shift with respect to the Larmor frequency to higher or lower frequencies depending on the strength of spin orbit interaction and distance between the beams. The two-beam spin noise spectroscopy could find applications in experimental studies of semiconductors, emergent materials, and many other systems. [ABSTRACT FROM AUTHOR]

We report both photon- and phonon-assisted tunneling transitions in a linear array of three quantum dots, which can only be understood by considering the full three-dimensionality of the charge stability diagram. Such tunneling transitions potentially contribute to leakage of qubits defined in this system. A detailed understanding of these transitions is important as they become more abundant and complex to analyze as quantum dot arrays are scaled up. [ABSTRACT FROM AUTHOR]

We review pioneering and recent studies of the conductivity of solid state systems at terahertz frequencies. A variety of theoretical formalisms that describe the terahertz conductivity of bulk, mesoscopic and nanoscale materials are outlined, and their validity and limitations are given. Experimental highlights are discussed from studies of inorganic semiconductors, organic materials (such as graphene, carbon nanotubes and polymers), metallic films and strongly correlated electron systems including superconductors. [ABSTRACT FROM AUTHOR]

The spin dynamics of electrons in low-symmetry quantum wells (QWs) under conditions of interband excitation by ultrashort unpolarized light pulses is investigated. It is shown that after the transmission, spin polarization appears in the system after a time comparable with the electron momentum relaxation time for an electron pulse and then vanishes. The microscopic theory of spin orientation of electrons by optical pulses carrying zero angular momentum is developed for asymmetric QWs grown from semiconductors with the zinc blende lattice along the [110] crystallographic direction. Pumping with unpolarized light in such structures in the normal incidence geometry induces a spin in the QW plane along the $$[1\bar 10]$$ axis. [ABSTRACT FROM AUTHOR]

Room temperature electronic diffusion is studied in 3 μm thick epitaxial p+ GaAs lift-off films using a novel circularly polarized photoluminescence microscope. The method is equivalent to using a standard optical microscope and provides a contactless means to measure both the charge (L) and spin (Ls) diffusion lengths simultaneously. The measured values of L and Ls are in excellent agreement with the spatially averaged polarization and a sharp reduction in these two quantities (L from 21.3 to 1.2 μm and Ls from 1.3 to 0.8 μm) is found with increasing surface recombination velocity. Outward diffusion results in a factor of 10 increase in the polarization at the excitation spot. The range of materials to which the technique can be applied, as well as a comparison with other existing methods for the measurement of spin diffusion, is discussed. [ABSTRACT FROM AUTHOR]

We briefly review recent achievements in experimental and theoretical studies of the spin dynamics of electrons and trions under optical pulse-train excitation. The microscopic origin of spin coherence generation, control and detection by means of light is uncovered. The specific features of spin-Faraday, Kerr, and ellipticity signals are analyzed. We show that these effects provide complementary information about spin dynamics. The equilibrium spin dynamics probed by the spin noise spectroscopy is also discussed. [ABSTRACT FROM AUTHOR]

Spin noise spectroscopy (SNS) is the perfect tool to investigate electron spin dynamics in semiconductors at thermal equilibrium. We simulate SNS measurements which utilize real-time fast Fourier transformation instead of an ordinary spectrum analyzer and show that ultrafast digitizers with low resolution enable surprisingly sensitive, high bandwidth SNS in the presence of strong optical background shot noise. The simulations reveal that optimized input load at the digitizer is crucial for efficient spin noise detection while the resolution of the digitizer, i.e., the bit depth, influences the sensitivity rather weakly. [ABSTRACT FROM AUTHOR]

We report on microwave (mw) radiation induced electric currents in (Cd,Mn)Te/(Cd,Mg)Te and InAs/(In,Ga)As quantum wells subjected to an external in-plane magnetic field. The current generation is attributed to the spin-dependent energy relaxation of electrons heated by mw radiation. The relaxation produces equal and oppositely directed electron flows in the spin-up and spin-down subbands yielding a pure spin current. The Zeeman splitting of the subbands in the magnetic field leads to the conversion of the spin flow into a spin-polarized electric current. [ABSTRACT FROM AUTHOR]

A time-resolved Kerr rotation system with a rotatable in-plane magnetic field has been constructed to study anisotropic spin relaxation of electrons in semiconductors. A permanent magnet magic ring is placed on top of a motor-driven rotation stage (RS) to create the rotatable in-plane magnetic field. The RS is placed on a second translation stage to vary the local magnetic field around a sample. The in-plane magnetic field in such a system varies from 0.05 to 0.95 T, with full-round 360° rotatablity, thus offering a convenient and low-cost way to study the anisotropy of spin dynamics in semiconductors. Its performance was demonstrated via measurement of the anisotropy of the spin dephasing time (SDT) of electrons in a two-dimensional electron system embedded in a GaAs/Al0.35Ga0.65As heterostructure. The SDT with B∥[110] was observed to be 10% larger than that with B∥[110], consistent with the results of others, which was measured via rotating sample. [ABSTRACT FROM AUTHOR]

We report here on anisotropy of spin polarization obtained in lateral all-semiconductor, all-electrical spin injection devices employing p+-(Ga,Mn)As/n+-GaAs Esaki diode structures as spin aligning contacts, resulting from the dependence of the efficiency of spin tunneling on the orientation of spins with respect to different crystallographic directions. We observed an in-plane anisotropy of 8% in the case of spins oriented either along [110] or [110] direction and 25% anisotropy between in-plane and perpendicular-to-plane orientations of spins. [ABSTRACT FROM AUTHOR]

Both structure and bulk inversion asymmetry in modulation-doped (001)-grown GaAs quantum wells were investigated employing the magnetic field induced photogalvanic effect. We demonstrate that the structure inversion asymmetry (SIA) can be accurately tailored by the delta-doping layer position. Symmetrically doped structures exhibit a substantial SIA due to impurity segregation during the growth process. Tuning the SIA by the delta-doping position, we can grow samples with almost equal degrees of structure and bulk inversion asymmetry. [ABSTRACT FROM AUTHOR]

We propose and demonstrate spin noise spectroscopy as an efficient, noncontact method to measure doping concentrations in semiconductors with high accuracy and high spatial resolution. In a proof of concept study, two different doping levels in a silicon-doped GaAs stack are depth resolved with a relative accuracy of up to 5% and a spatial accuracy better than 50 μm. The method promises three-dimensional doping measurements in direct semiconductors with submicrometer resolution even at extremely low doping concentrations. [ABSTRACT FROM AUTHOR]

We have investigated the spin transport in ferromagnet (FM)/semiconductor (SC)/ferromagnet (FM) structures with a central SC barrier region exhibiting cubic Dresselhaus spin-orbit-interaction (SOI). The energy profile of the barrier is assumed to be a square with height V and thickness d along z-direction. The magnetoresistance (MR) ratio has been calculated for three different barriers, GaAs, GaSb, and GaAs without SOI as a function of barrier thickness. We have found that the MR ratio has a negative value for GaAs barrier with SOI except for very thin barrier thickness. In the case of GaSb barrier, the MR ratio changes sign from negative to positive with increasing the barrier thickness. Also, we have calculated the MR ratio with changing the spin coupling constant. [ABSTRACT FROM AUTHOR]

The level of the chemical potential is a fundamental parameter of the electronic structure of a physical system, which consequently plays an important role in defining the properties of active electrical devices. We directly measure the chemical potential shift in the relativistic band structure of the ferromagnetic semiconductor (Ga,Mn)As, controlled by changes in its magnetic order parameter. Our device comprises a non-magnetic aluminum single electron channel capacitively coupled to the (Ga,Mn)As gate electrode. The chemical potential shifts of the gate are directly read out from the shifts in the Coulomb blockade oscillations of the single electron transistor. The experiments introduce a concept of spin gating electrical current. In our spin transistor spin manipulation is completely removed from the electrical current carrying channel. [ABSTRACT FROM AUTHOR]