A theory of magnetic impurities in a 2D electron gas quantized by a strong magnetic field is formulated in terms of Friedel-Anderson theory of resonance impurity scattering. It is shown that this scattering results in an appearance of bound Landau states with zero angular moment between the Landau subbands. The resonance scattering is spin selective, and it results in a strong spin polarization of Landau states, as well as in a noticeable magnetic field dependence of the $g$ factor and the crystal field splitting of the impurity $d$ levels.
Resonant scattering at the atomic absorbates in graphene was investigated recently in relation with the transport and gap opening problems. Attaching an impurity atom to graphene is believed to lead to the creation of unusual zero energy localized electron states. This paper aims to describe the behavior of the localized impurity-induced levels in graphene in a quantizing magnetic field. It is shown that in the magnetic field the impurity level effectively hybridizes with one of the n=0 Landau level states and splits into two opposite-energy states. The new hybridized state is doubly occupied,…
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…
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.
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…
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…
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 ex…
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 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…
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…
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…
Measurement of miniband parameters of a doped superlattice by photoluminescence in high magnetic fields
我们研究了GaAs/Al $_{0.21}$ Ga $_{0.79}$ As组成的50/50超晶格，调制掺杂Si，以产生每个超晶格周期的$n=1.4\times 10^{12}$ cm $^{-2}$电子。调制掺杂量身定制，以避免形成的Tamm状态，和光致发光由于从扩展的超晶格状态的带间跃迁被检测到。通过研究量子化磁场对超晶格光致发光的影响，可以得到能带宽度、电子-空穴对的约化有效质量和带隙重整化。
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 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…
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…
The thermoelectric effect is the generation of an electrical voltage from a temperature gradient in a solid material due to the diffusion of free charge carriers from hot to cold. Identifying materials with large thermoelectric response is crucial for the development of novel electric generators and coolers. In this paper we consider theoretically the thermopower of Dirac/Weyl semimetals subjected to a quantizing magnetic field. We contrast their thermoelectric properties with those of traditional heavily-doped semiconductors and we show that, under a sufficiently large magnetic field, the the…
We demonstrate that chirality of the electron scattering in Weyl semimetals leads to the formation of magnetic chemical bonds for molecular states of a pair of impurities. The effect is associated with the presence of time-reversal symmetry breaking terms in the Hamiltonian which drive a crossover from s- to p-wave scattering. The profiles of the corresponding molecular orbitals and their spin polarizations are defined by the relative orientation of the lines connecting two Weyl nodes and two impurities. The magnetic character of the molecular orbitals and their tunability open the way for usi…
Based on a self-consistent $t$-matrix approximation, we explore the influence of magnetic and nonmagnetic doping on the surface electronic states and conductivity of topological insulators. We show that warping parameter has a crucial impact on the density of states and dc conductivity of the doped surfaces. As the warping strength is increased, the surface density of states at high energies is suppressed and the resonant states induced by impurities in the vicinity of the Dirac point gradually disappear. It is found that nonmagnetic impurities break electron-hole symmetry at low warping stren…
The dependences of the transport scattering time τt, quantum lifetime τq, and their ratio τt/τq on the density ne of the electron gas in modulation-doped single GaAs quantum wells with AlAs/GaAs short-period super-lattice barriers are investigated. The experimental dependences are explained in terms of electron scattering by remote ionized donors with an effective two-dimensional concentration n*R and background impurities with a three-dimensional concentration nB. An expression for n*R(ne) is obtained including the contribution of X-valley electrons localized in AlAs layers to the suppression…
Tuning of the electronic properties of pre-synthesized colloidal semiconductor nanocrystals (NCs) by doping plays a key role in the prospect of implementing them in printed electronics devices such as transistors, and photodetectors. While such impurity doping reactions have already been introduced, the understanding of the doping process, the nature of interaction between the impurity and host atoms, and the conditions affecting the solubility limit of impurities in nanocrystals are still unclear. Here, we used a post-synthesis diffusion based doping reaction to introduce Ag impurities into I…
We study odd-parity nematic superconductivity in doped topological insulators in presence of surface magnetic impurities. The peculiar surface subgap spectrum, characterized by a Majorana flatband, nodal cones and the surface states of the parent topological insulator, gives rise to an overall ferromagnetic RKKY interactions between the surface impurities. An additional coupling between the impurities and a preemptive chiral order parameter promote a surface time-reversal symmetry breaking solution at the surface of the system. We discuss the relevant scenarios and suggest to engineer surface …
Anomalous Localization in Magnetically Doped Two-Dimensional Topological Insulators
Instituto de Física Teórica, São Paulo State University（圣保罗州立大学理论物理研究所）；School of Physics, Trinity College Dublin（都柏林三一学院物理学院）；Advanced Materials and Bioengineering Research (AMBER) Centre, Trinity College Dublin（都柏林三一学院先进材料与生物工程研究中心）；Instituto de Física, Universidade Federal do Rio de Janeiro（里约热内卢联邦大学物理研究所）
We explore theoretically the magnetoresistance of Weyl semimetals in transversal magnetic fields away from charge neutrality. The analysis within the self-consistent Born approximation is done for the two different models of disorder: (i) short-range impurties and (ii) charged (Coulomb) impurities. For these models of disorder, we calculate the conductivity away from charge neutrality point as well as the Hall conductivity, and analyze the transversal magnetoresistance (TMR) and Shubnikov-de Haas oscillations for both types of disorder. We further consider a model with Weyl nodes shifted in en…
We study the RKKY interaction of magnetic impurities in the $α-\mathcal{T}_3$ model which hosts pseudospin-1 fermions with two dispersive and one flat bands. By using the effective low-energy Hamiltonian we calculate the RKKY coupling for impurities placed on the same or different sublattices. We find that there are three types of interaction, which depend on the model parameter defining the relative strength of hoppings between sublattices, two of them can be reduced to graphene case while the third one is new and is due to the presence of a flat zero-energy band. We derive general analytical…
We study the photon-dressed electronic band structure of topological insulator thin films which could be also doped doped by magnetic impurities in response to an off-resonance time-periodic electromagnetic field. The thin films irradiated by a circularly polarized light undergo phase transition, in a driven system made by and a fascinating feature of distinct phases emerges in the phase diagram depending on the parameters such as frequency, intensity and polarization of the light. As a particular case, quantum anomalous Hall insulator phase is induced purely by the light-induced mass term wit…
