We study the transport properties of two dimensional electron systems with strong Rashba spin-orbit coupling (SOC) doped with interacting magnetic impurities. Interactions between magnetic impurities cause the formation of magnetic clusters with temperature dependent mean sizes (CMSs) distributed randomly on the surface of the system. Treating magnetic clusters as scattering centers, by employing a generalized relaxation time approximation we obtain the non-equilibrium distribution functions of Rashba electrons in both regimes of above and below the band-crossing point (BCP) and present the explicit forms of the conductivity in terms of effective relaxation times. We demonstrate that the combined effects of SOC and magnetic clusters cause the system to be anisotropic and the magneto-resistance strongly depends on both the clusters' mean size and spin, the strengths of SOC and the location of Fermi energy with respect to the BCP. Our results show that there are many contrasts between the transport properties of the system in the two regimes of above and below the BCP. By comparing the anisotropic magneto-resistance (AMR) of the two dimensional Rashba systems with the surface AMR of three dimensional magnetic topological insulators, we also point out the differences between these systems.
We study a generic topological Kondo insulator system by performing a mean-field theoretic calculation within the frame-work of slave-boson protocol. We assume infinite Hubbard-type interaction among the localized electrons. The difference between the bulk metallic and insulating phases of the insulator is in the sign of nearest neighbor hopping of localized electrons. The hopping amplitude is positive for the metallic and negative for the insulating phase. The surface metallicity together with bulk insulation, however, requires very strong f electron localization. Furthermore, we find that th…
Explicit dependencies of the local density of states and the magnetization local density of states have been obtained around magnetic point defects in a two-dimensional electron gas with Rashba spin-orbit interaction . The expressions are given in the Born approximation for arbitrary magnitude and orientation of the defect magnetic moment, and for arbitrary size of the constant of spin-orbit interaction alpha/. On the basis of our asymptotically exact formulas a procedure for the determination of the constant alpha/ in STM experiments is proposed. The novel analytical results are compared with…
In this study, the Optical conductivity of substitutionary doped graphene is investigated in presence of the Rashba spin orbit coupling (RSOC). Calculations have been performed within the coherent potential approximation (CPA) beyond the Dirac cone approximation. Results of the current study demonstrate that the optical conductivity is increased by increasing the RSOC strength. Meanwhile it was observed that the anisotropy of the band energy results in a considerable anisotropic optical conductivity (AOC) in monolayer graphene. The sign and magnitude of this anisotropic conductivity was shown …
Using the Matsubara Green's function formalism we calculate the temperature dependence of the nonequilibrium spin polarization induced by an external electric field in the presence of spin-orbit coupling. The model Hamiltonian includes an isotropic k-cubed form of the Rashba spin-orbit interaction. Such a Hamiltonian captures the electronic and spin properties of two-dimensional electron (hole) gas at the surfaces or interfaces of transition metal oxides or in p-doped semiconductor heterostructures. The induced spin polarization is calculated for the nonmagnetic as well as magnetic electron/ho…
Spectral and transport properties of doped (or gated) graphene with long range charged impurities are discussed within the self-consistent Born approximation. It is shown how, for impurity concentrations $n_{imp}\gtrsim n$ a finite DOS appears at the Dirac point, the one-particle lifetime no longer scales linearly with the Fermi momentum, and the lineshapes in the spectral function become non-lorentzian. These behaviors are different from the results calculated within the Born approximation. We also calculate the optical conductivity from the Kubo formula by using the self-consistently calcula…
To induce a strong Rashba effective magnetic field and enhance its sensitivity to an external electric field, we propose acceptor doping in quantum wells. The acceptors are doped at the center of the well, and donors are doped in the barrier layers to compensate the acceptors and induce conduction electrons. In strongly doped wells, the electric field on these conduction electrons is easily changed by a weak external electric field, by virtue of the strong internal electric field between the acceptors and donors and the resulting high triangle potential barrier induced in the well. As a result…
We study the spin transport and polarization properties of manganese-doped dual-guanine molecules connected to graphene leads using non-equilibrium Green's function method. It is shown that a manganese doped dual-guanine molecule is a biological semiconductor and behaves as a prefect spin filter. We show that this semiconductor can behave as a spin switch when the Rashba spin-orbit interaction is considered. In addition, it is shown that, a large conductance is observed due to the Fano-Kondo-Rashba resonance effect.
Thermoelectric properties of Graphene Nanoribbons doped by magnetic impurities Fe and Co are carried out in room temperature. We report on a study of the band structure dependent properties such as electrical conductivity, charge of carriers and Seebeck coefficients. We investigate the thermoelectric properties using the Semi-classical Boltzmann method. The electronic band structure of doped nanoribbons are evaluated by using density-functional theory in which the Hubbard interaction is considered. In this work we compare the different types of the nanoribbons and their thermoelectric features…
A dilute distribution of magnetic impurities is assumed to be present in doped graphene. We calculate the interaction energy between two magnetic impurities which are coupled via the indirect-exchange or Ruderman-Kittel-Kasuva-Yosida (RKKY) interaction by the doped conduction electrons. The current model is a half-filled $AB$-lattice structure. Our calculations are based on the retarded lattice Green's function formalism in momentum-energy space which is employed in linear response theory to determine the magnetic susceptibility in coordinate space. Analytic results are obtained for gapped gra…
We investigate nonperturbatively the effect of a magnetic dopant impurity on the edge transport of a quantum spin Hall (QSH) insulator. We show that for a strongly coupled magnetic dopant located near the edge of a system, a pair of transmission anti-resonances appear. When the chemical potential is on resonance, interaction effects broaden the anti-resonance width with decreasing temperature, thus suppressing transport for both repulsive and moderately attractive interactions. Consequences for the recently observed QSH insulating phase of the $1$-T$^{\prime}$ of WTe$_2$ are briefly discussed.
We investigate the ballistic electron transport in a monolayer graphene with configurational averaged impurities, located between two clean graphene leads. It is shown that the electron transmission are strongly dependent on the concentration of impurities and the incident energy. In turn, the conductance computed using the Landauer formalism shows a similar behavior to those found in experimental works as a function of the applied voltage for different concentrations of impurities in the limit of low temperatures. In the limit of zero bias voltage, the conductance shows a minimum value which …
Combining ab initio calculations and effective models derived from them, we discuss the electronic structure of oxygen doped gold chains when one Au atom is replaced by any transition-metal atom of the $3d$ series. The effect of O doping is to bring extended Au $5d_{xz}$ and $5d_{yz}$ states to the Fermi level, which together with the Au states of zero angular momentum projection, lead to three possible channels for the screening of the magnetism of the impurity. For most 3d impurities the expected physics is similar to that of the underscreened Kondo model, with singular Fermi liquid behavior…
Electronic transport properties in armchair shaped edges graphene nanoribbons (AGNRs) doped various impurities have been simulated by the non-equilibrium Green's function approach combined with the first principle calculation based on the density functional theory. We have observed that impurity levels appear in electronic struc-tures, and that the quantization of transmission function is moderated for doped AGNRs. The I-V characteristic can be computed from the transmission function. Our simulation results show that AGNRs doped impurities have higher conductance than the non-doped one.
We present a theory for the electronic and magneto-optical properties of spherical quantum dots consisting of an inner core surrounded by an outer shell. This core-shell quantum dot is doped by magnetic Mn impurities all of which are implanted at a preselected radius on a spherical surface within the dot. The spherical symmetry of the dot is broken by the application of an external magnetic field. The electronic states in the presence of a magnetic field are treated in an effective mass model which includes the s-d and p-d exchange interaction with localized Mn d electrons. The strain in the q…
The Spin Hall Effect (SHE) is a promising way for transforming charge currents into spin currents in spintronic devices. Large values of the Spin Hall Angle, the characteristic parameter of the yield of this transformation, have been recently found in noble metals doped with nonmagnetic impurities. We show that this can be explained by resonant scattering off impurity states split by the spin-orbit interaction. We apply our calculation to the interpretation of experiments on copper doped with 5d impurities and we describe the conditions to obtain the largest effects.
We propose a model of three-dimensional topological insulators consisting of weakly coupled electron- and hole-gas layers with Rashba spin-orbit interaction stacked along a given axis. We show that in the presence of strong electron-electron interactions the system realizes a fractional strong topological insulator, where the rotational symmetry and condensation energy arguments still allow us to treat the problem as quasi-one-dimensional with bosonization techniques. We also show that if Rashba and Dresselhaus spin-orbit interaction terms are equally strong, by doping the system with magnetic…
We consider a wire network of ferromagnetic impurities on the surface of an $s$-wave superconductor with strong Rashba spin-orbit interaction. Within the topological phase, zero-energy Majorana fermions appear at wire end-points as well as at junctions between an odd number of wire segments, while no low-energy states are present at junctions between an even number of wire segments, providing strong experimentally accessible signatures for Majorana fermions. We also investigate the quasiparticle energy gap with respect to varying the Rashba spin-orbit coupling and magnetic impurity strength.
Motivated by the recently observed sublattice asymmetry of substitutional nitrogen impurities in CVD grown graphene, we show, in a mathematically transparent manner, that oscillations in the local density of states driven by the presence of substitutional impurities are responsible for breaking the sublattice symmetry. While these oscillations are normally averaged out in the case of randomly dispersed impurities, in graphene they have either the same, or very nearly the same, periodicity as the lattice. As a result, the total interaction energy of randomly distributed impurities embedded in t…
The lack of some spatial symmetries in planar devices with Rashba spin-orbit interaction opens the possibility of producing spin polarized electrical currents in absence of external magnetic field or magnetic impurities. We study how the direction of the spin polarization of the current is related to spatial symmetries of the device. As an example of these relations we study numerically the spin-resolved current in graphene nanoribbons. Different configurations are explored and analyzed to demonstrate that graphene nanoflakes may be used as excellent spintronic devices in an all-electrical set…
Doping a semiconductor quantum dot with just a single impurity atom can completely transform its physical properties. Here, we report and analyze the magnetic circular dichroism (MCD) spectra of colloidal CdSe quantum dot samples containing on average fewer than one Mn2+ per quantum dot. Even at this sub-single-dopant level, the low-temperature low-field data are dominated by impurity-induced Zeeman splittings caused by dopant-carrier sp-d exchange. Unlike in more heavily doped quantum dots, however, the MCD intensity at the first CdSe exciton shows a field-induced sign flip as the field stren…
We present the magnetic phase diagram of artificial H$_2$ molecule in lateral quantum dots doped with magnetic impurities as a function of external magnetic field and plunger gate voltage. The onset of Mn-Mn antiferromagnetic-ferromagnetic transition follows the electron spin singlet-triplet transition. We deploy a configuration-interaction method to exactly diagonalize the electron-Mn Hamiltonian and map it to an effective Mn-Mn Heisenberg Hamiltonian. We find that Mn-Mn exchange coupling can be described by RKKY-interaction/magnetic-polaron in weak/strong electron-Mn coupling at low/high mag…
We demonstrate theoretically that a new system quantum well can realize the topological transition based on the 16-band kp model. Utilizing the strain introduced by the doped impurities, the band anti crossing induced by the doped nitrogen and valence band anti crossing induced by the doped bismuth, the band gap of the quantum well is rapidly decreased and even becomes negative. As a result, the topological transitions arise. Furthermore, the band gap as a function of the concentration of nitrogen and bismuth is calculated, where the negative gap corresponds to the topological phase. Noting th…
Electron spin transport and dynamics are investigated in a single, high-mobility, modulation-doped, GaAs quantum well using ultrafast two-color Kerr-rotation micro-spectroscopy, supported by qualitative kinetic theory simulations of spin diffusion and transport. Evolution of the spins is governed by the Dresselhaus bulk and Rashba structural inversion asymmetries, which manifest as an effective magnetic field that can be extracted directly from the experimental coherent spin precession. A spin precession length L-SOI is defined as one complete precession in the effective magnetic field. It is …
We study the electron transport in a magnetically doped three dimensional topological insulator (TI) by taking the effects of impurity-impurity exchange interactions into account. The interactions between magnetic impurities give rise to the formation of {\it magnetic clusters} with temperature dependent mean sizes, randomly distributed on the surface of the TI. Instead of dealing with single magnetic impurities, we consider surface Dirac electrons to be scattered off magnetic clusters, and define the scattering potential in terms of clusters mean sizes. Within the semiclassical Boltzmann appr…
Electric and thermoelectric properties of silicene nanoribbons doped with Al and P impurity atoms are investigated theoretically for both antiparallel and parallel orientations of the edge magnetic moments. In the former case, appropriately arranged impurities can lead to a net magnetic moment and thus also to spin thermoelectric effects. In the latter case, in turn, spin thermoelectric effects also occur in the absence of impurities. Numerical results based on ab-initio calculations show that the spin thermopower can be considerably enhanced by the impurities.
A significant advance toward achieving practical applications of graphene as a two-dimensional material in nanoelectronics would be provided by successful synthesis of both n-type and p-type doped graphene. However reliable doping and a thorough understanding of carrier transport in the presence of charged impurities governed by ionized donors or acceptors in the graphene lattice are still lacking. Here we report experimental realization of few-layer nitrogen-doped (N-doped) graphene sheets by chemical vapor deposition of organic molecule 1, 3, 5-triazine on Cu metal catalyst. By reducing the …
We present a theoretical study on the effect of radiation on the mangetoresistance of two-dimensional electron systems with strong Rashba spint-orbit coupling. We want to study the interplay between two well-known effects in these electron systems: the radiation-induced resistance oscillations and the typical beating pattern of systems with intense Rashba interaction. We analytically derive an exact solution for the electron wave function corresponding to a total Hamiltonian with Rashba and radiation terms. We consider a perturbation treatment for elastic scattering due to charged impurities t…
The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction of magnetic impurities in a superconductor exponentially decreases when the distance $r$ between them is larger than the superconductor's coherence length, because this interaction is mediated by quasiparticles which have a gap in their energy spectrum. At the same time, the spin-singlet superconducting condensate was always assumed to stay neutral to magnetic impurities. Due to a spin-orbit coupling (SOC), however, Cooper pairs gain an admixture of spin-triplet correlated states which provide for a link between impurity spins and an s-wave …
In the present theoretical work we have considered impurities, either boron or phosphorous, located at different substitutional sites in silicon quantum dots (Si-QDs) with diameters around 1.5\,nm, embedded in a SiO2 matrix. Formation energy calculations reveal that the most energetically-favored doping sites are inside the QD and at the Si/SiO2 interface for P and B impurities, respectively. Furthermore, electron and hole transport calculations show in all the cases a strong reduction of the minimum voltage threshold, and a corresponding increase of the total current in the low-voltage regime…
Evaluation of the Bychkov- Rashba Field from the Spin Resonance of Electrons in a Si Quantum Well
从调制掺杂的SiGe/Si/SiGe量子阱结构中的二维（2D）传导电子的自旋共振，我们发现线加宽（退相时间）和g因子的2D各向异性。我们表明，这些可以解释一致的Bychkov-Rashba（BR）的字段，在这里是占主导地位的电子运动和自旋之间的耦合。我们得到的BR参数α = 1.1 e-12 eV cm -三个数量级相比，III-V阱小。外推低电子浓度，我们得到的硅导带的g因子为2.00073+/-0.00010。
Indirect exchange interaction between magnetic impurities in one dimensional systems is a matter of long discussions since Kittel has established that in the asymptotic limit it decays as the inverse of distance x between the impurities. In this work we investigate this problem in a quantum wire with Rashba spin-orbit coupling (SOC). By employing a second order perturbation theory we find that one additional oscillatory term appears in each of the RKKY, the Dzaloshinkii-Moryia and the Ising couplings. Remarkably, these extra terms resulting from the spin precession of the conduction electrons …
This work presents an analytic angular differential cross section formula for the electromagnetic radiation field assisted electron scattering by %% was on impurities in semiconductors. These impurities are approximated with various model potentials. The scattered electrons are described by the well-known Volkov wave function, which has been used describe strong laser field matter interaction for more than half a century, %% I would remove this time reference for clarity which exactly describes the interaction of the electron with the external oscillating field. These calculations show that th…
We investigate the induced orbital magnetization density in a Rashba electron gas with magnetic impurities. Relying on classical electrodynamics, we obtain this quantity through the bound currents composed of a paramagnetic and a diamagnetic-like contribution which emerge from the spin-orbit interaction. Similar to Friedel charge ripples, the bound currents and the orbital magnetization density oscillate as function of distance away from the impurity with characteristic wavelengths defined by the Fermi energy and the strength of the Rashba spin-orbit interaction. The net induced orbital magnet…
We study the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in p-doped transition metal dichalcogenides such as MoS$_2$ and WS$_2$. We consider magnetic impurities hybridized to the Mo d-orbitals characteristic of the valence bands. Using the Matsubara Green's function formalism, we obtain the two-impurity interaction vs their separation and chemical potential of the system, accounting for the important angular dependence which reflects the underlying triangular lattice symmetry. The inclusion of the valence band valley at the $Γ$ point results in a strong enhancement of the interaction. Ele…
The magnetic properties of graphene-related materials and in particular the spin-polarised edge states predicted for pristine graphene nanoribbons (GNRs) with certain edge geometries have received much attention recently due to a range of possible technological applications. However, the magnetic properties of pristine GNRs are not predicted to be particularly robust in the presence of edge disorder. In this work, we examine the magnetic properties of GNRs doped with transition-metal atoms using a combination of mean-field Hubbard and Density Functional Theory techniques. The effect of impurit…
Magnetism Induced by Periodically Driven Non-Magnetic Impurities on Surfaces with Spin-Orbit Coupling
Universidad del País Vasco UPV/EHU（巴斯克大学）；Centro de Física de Materiales (CFM/MPC) CSIC-UPV/EHU（巴斯克材料物理中心）；Donostia International Physics Center (DIPC)（圣塞巴斯蒂安国际物理中心）；EHU Quantum Center（巴斯克大学量子中心）
We consider a Josephson junction bilayer consisting of two tunnel-coupled two-dimensional electron gas layers with Rashba spin-orbit interaction, proximitized by a top and bottom $s$-wave superconductor with phase difference $ϕ$ close to $π$. We show that, in the presence of a finite weak in-plane Zeeman field, the bilayer can be driven into a second order topological superconducting phase, hosting two Majorana corner states (MCSs). If $ϕ=π$, in a rectangular geometry, these zero-energy bound states are located at two opposite corners determined by the direction of the Zeeman field. If the pha…
Magnetically-doped graphene systems are potential candidates for application in future spintronic devices. A key step is to understand the pairwise interactions between magnetic impurities embedded in graphene that are mediated by the graphene conduction electrons. A large number of studies have been undertaken to investigate the indirect exchange, or RKKY, interactions in graphene. Many of these studies report a decay rate faster than expected for a 2-dimensional material and the absence of the usual distance dependent oscillations. In this review we summarize the techniques used to calculate…
Magnetic quantum oscillations (MQOs) have been widely used as a tool for probing Fermi surfaces. The shape and topology of the Fermi surface and the related physical parameters, such as the cyclotron mass and relaxation time, can be verified by carefully analyzing the frequency, amplitude, and phase of MQOs. In particular, phase analysis, from which we can obtain the Berry phase, has received much attention with the growing interest in the topology of condensed matter physics. Here, beyond the conventional uses of MQOs, we show that MQOs can be used to determine the Fermi surface magnetization…
In this paper we construct a one-dimensional insulator with an approximate chiral symmetry belonging to the AIII class and discuss its properties. The construction principle is the intentional pollution of the edge of a two-dimensional quantum spin Hall insulator with magnetic impurities. The resulting bound states hybridize and disperse along the edge. We discuss under which circumstances this chain possesses zero-dimensional boundary modes on the level of an effective low-energy theory. The main appeal of our construction is the independence on details of the impurity lattice: the zero modes…
We study the magnetic properties of topological insulators doped with isoelectronic magnetic impurities. We obtain that at zero temperature the impurities order ferromagnetically, but when raising the temperature the topological insulator undergoes a first order phase transition to a spin density wave phase before the system reaches the paramagnetic phase. The origin of this phase is the non-trivial dependence of the topological insulator spin susceptibility on the momentum. We analyze the coupling of the non-uniform magnetic phase with the Dirac electronic system that occurs at the surfaces o…
We show that a chain of nonmagnetic impurities deposited on a fully gapped two- or three-dimensional superconductor can become a topological one-dimensional superconductor with protected Majorana bound states at its end. A prerequisite is that the pairing potential of the underlying superconductor breaks the spin-rotation symmetry, as it is generically the case in systems with strong spin-orbit coupling. We illustrate this mechanism for a spinless triplet-superconductor p+ip and a time-reversal symmetric Rashba superconductor with a mixture of singlet and triplet pairing. For the latter, we sh…
We study theoretically the statistical properties of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between localized magnetic moments in a disordered two-dimensional electron gas with both Rashba and Dresselhaus spin-orbit couplings. Averaging over disorder, the static spin susceptibility tensor is evaluated diagrammatically in the mesoscopic (phase-coherent) regime. The disorder-averaged susceptibility leads to a twisted exchange interaction suppressed exponentially with distance, whereas the second-order correlations, which determine the fluctuations (variance) of the RKKY energy, dec…
