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1.
The exciton states in a CdTe quantum ring subjected to an external magnetic field containing a single magnetic impurity are investigated. We have used the multiband approximation which includes the heavy hole–light hole coupling effects. The electron–hole spin interactions and the s, p–d interactions between the electron, the hole and the magnetic impurity are also included. The exciton energy levels and optical transitions are evaluated using the exact diagonalization scheme. We show that due to the spin interactions it is possible to change the bright exciton state into the dark state and vice versa with the help of a magnetic field. We propose a new route to experimentally estimate the s, p–d spin interaction constants. 相似文献
2.
K.N. Shrivastava 《Solid State Communications》1984,51(8):631-633
A new Hamiltonian for the interaction of magnetic impurity spin with the conduction electrons is proposed. It is found that the conduction electrons may be condensed into the spin levels. For single impurity, the exact eigenstates are found. In the case of many impurities, virtual electron exchange is predicted for the first time. A single fermion and a single phonon operator interaction leads to hybrid interaction between bands of electrons along with some interesting effects. 相似文献
3.
Reinhold Egger 《Zeitschrift für Physik B Condensed Matter》1996,103(2):221-223
The spin and charge correlations induced in the conduction electron sea by the presence of a spin-1=2 magnetic impurity are investigated for one-dimensional electrons. For correlated conduction electrons, the RKKY interaction between magnetic impurities exhibits only a slow algebraic decay with distance. Increasing the exchange coupling between conduction electrons and magnetic impurity leads to a competition between the RKKY interaction and the Kondo effect. For a two-impurity model, we study the influence of the electronic correlations on this competition. Furthermore, the Kondo screening cloud and the local spin susceptibility far away from a magnetic impurity are discussed. 相似文献
4.
We investigate the scanning tunneling spectroscopy (STS) of a two-orbital Anderson impurity
adsorbed on a metallic surface by using the numerical renormalization group (NRG) method. The density
of state of magnetic impurity and the local conduction electron are calculated. We obtain the Fano
resonance line shape in the STM conductance at zero temperature. For the impurity atom with
antiferromagnetic inter-orbital exchange interaction and a spin singlet ground state, we show that a
dip in the STM spectra around zero bias voltage regime and side peaks of spin excitation can be
observed. The spin excitation energy is proportional to the exchange interaction strength. As the
exchange interaction is ferromagnetic, the underscreened Kondo effect dominates the low energy
properties of this system, and it gives rise to drastically different STM spectra as compared with the
spin singlet case. 相似文献
5.
本文采用含有非磁性杂质的二维t-J模型来描述掺锌的高温氧化物超导材料,并利用非均匀双时格林函数理论对有限尺寸的材料进行了数值计算.在 Fermion-Spin 理论框架下,我们分别研究了非磁性杂质引起的电荷和自旋的不均匀性及对材料正常态特性的影响.我们发现:一方面非磁性杂质锌对其附近的自旋反铁磁关联有强烈的影响,能使周围的最近邻关联函数的绝对值比均匀情况增加很多;另一方面,空位子会受到其周围自旋的影响而出现相应的分布不均匀性,进而又影响自旋关联的不均匀性.并且,围绕杂质锌能够形成自旋激发和空位激发的局域态. 相似文献
6.
P. Liu S.-J. Xiong 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(4):513-516
The spin Hall transport properties in a two-dimensional electron
system with both Rashba spin-orbit coupling (SOC) and magnetic
impurities are investigated. Electrons are scattered by impurities
through an exchange interaction that leads to spin flip-flop
processes and so changes the spin Hall effect induced by the SOC.
The spin Hall conductance is calculated in a 4-terminal system
using the Landauer-Buttiker formula and Green function approach.
In comparison with the simulation results on nonmagnetic
impurities doping systems, our results reveal that the spin Hall
conductance is still nonzero in a system with a large density of
magnetic impurities and a finite intensity of the exchange
interaction between the electrons and impurities, and its sign may
be altered when the doping density and interaction strength are
large enough. 相似文献
7.
8.
We investigate the ground and excited states of interacting electrons in a quantum point contact using an exact diagonalization method. We find that strongly localized states in the point contact appear when a new transverse conductance channel opens and longitudinal resonant level is formed due to momentum mismatch. These localized states form magnetic impurity states which are stable in a finite regime of chemical potential and excitation energy. Interestingly, these magnetic impurities have ferromagnetic coupling, which sheds light on the experimentally observed puzzling coexistence of Kondo correlation and spin filtering in a quantum point contact. 相似文献
9.
The spin transport as the current flows through an impurity in a one-dimensional conductor is analyzed. The interacting electrons
are described in terms of the Luttinger liquid theory. Both the Coulomb and short-range interactions are considered; the latter
appears when the gate screens the long-range part of the Coulomb potential. The cases of magnetic and nonmagnetic impurities
are considered. It has been revealed that, for a magnetic impurity, the electric current flow induces the generation of the
spin current, which has direct and alternating components. At low temperatures and voltages, the current can be completely
spin-polarized. For a nonmagnetic impurity, the spin current generation is absent. The spin current flowing though the wire
affects the current-voltage characteristic for both magnetic and nonmagnetic impurities. The results have been obtained for
a rather strong electron-electron interaction. 相似文献
10.
Using the Hubbard model in the framework of the tight-binding formulation, we studied the effects of the electron–electron (e–e) interaction on the indirect magnetic exchange coupling between the magnetic impurities embedded in triangular graphene nanoflakes. The results show that the magnitude of the coupling enhances in the presence of the e–e interaction and Rashba spin–orbit interaction (RSOI). The RKKY coupling magnitude depends on the impurity positions in nanoflake and the size of the system, as well. 相似文献
11.
The dependence of the width of the spectral function of electrons and holes on the wavevector and excitation energy in a 2D
electron system with spin-orbit interaction caused by structural inversion asymmetry is analyzed in the G
0
W
0 approximation. It is shown that an additional (relative to the generation of electron-hole pairs) channel of hole decay due
to emission of a plasmon appears in the case of low electron density. Noticeable spin asymmetry of the spectral function width
appears in the region of electron excitations. 相似文献
12.
Dunkan Martínez Álvaro Díaz-Fernández Pedro A. Orellana Francisco Domínguez-Adame 《Annalen der Physik》2023,535(6):2300072
Topological superconductors are foreseen as good candidates for the search of Majorana zero modes, where they appear as edge states and can be used for quantum computation. In this context, it becomes necessary to study the robustness and behavior of electron states in topological superconductors when a magnetic or non-magnetic impurity is present. The focus is on scattering resonances in the bands and on spin texture to know what the spin behavior of the electrons in the system will be. It is found that the scattering resonances appear outside the superconducting gap, thus providing evidence of topological robustness. Non-trivial and anisotropic spin textures related to the Dzyaloshinskii–Moriya interaction are also found. The spin textures show a Ruderman–Kittel–Kasuya–Yosida interaction governed by Friedel oscillations. It is believed that the results are useful for further studies which consider many-point-impurity scattering or a more structured impurity potential with a finite range. 相似文献
13.
《Physica E: Low-dimensional Systems and Nanostructures》2011,43(10):2493-2496
Coherent spin precession of electrons and excitons is observed in charge tunable InP quantum dots under the transverse magnetic field by means of time-resolved Kerr rotation. In a quantum dot doped by one electron, spin precession of the doped electron in the quantum dot starts out of phase with spin precession of the doped electrons in a GaAs substrate just after a trion is formed and persists for more than 2 ns even after the trion recombines. Simultaneously spin precession of a trion (hole) starts. Observation of spin precession of both a doped electron and a trion (hole) confirms creating coherent superposition of an electron and a trion as the initialization process of spin of doped electrons in quantum dots. In a neutral quantum dot, the exciton spin precession starts out of phase with spin precession of the doped electrons in a GaAs substrate and the precession frequency does not converge to 0 at the zero field limit. It contains the electron–hole exchange interaction and corresponds to the splitting between bright and dark excitons under the transverse magnetic field. 相似文献
14.
M. Poggio R.C. Myers G.M. Steeves N.P. Stern A.C. Gossard D.D. Awschalom 《Physica E: Low-dimensional Systems and Nanostructures》2006,35(2):264
Spin interactions are studied between conduction band electrons in GaAs heterostructures and local moments, specifically the spins of constituent lattice nuclei and of partially filled electronic shells of impurity atoms. Nuclear spin polarizations are addressed through the contact hyperfine interaction resulting in the development of a method for high-field optically detected nuclear magnetic resonance sensitive to 108 nuclei. This interaction is then used to generate nuclear spin polarization profiles within a single parabolic quantum well; the position of these nanometer-scale sheets of polarized nuclei can be shifted along the growth direction using an externally applied electric field. In order to directly investigate ion spin dynamics, doped GaMnAs quantum wells are fabricated in the regime of very low Mn concentrations. Measurements of coherent electron spin dynamics show an antiferromagnetic exchange between s-like conduction band electrons and electrons localized in the d-shell of the Mn impurities, which varies as a function of well width. 相似文献
15.
Recently the electron dephasing and energy relaxation due to different magnetic impurities have been extensively investigated experimentally in thin wires, and in this Letter these quantities are theoretically studied. It was shown earlier that a magnetic impurity in a metallic host with strong spin-orbit interaction experiences a surface anisotropy of the form H=K(d)(nS)(2) which causes size effects for impurities with integer spin. Here we show that the dephasing and the energy relaxation are influenced by the surface anisotropy in very different ways for integer spin having a singlet ground state. That must result also in strong size effects and may resolve the puzzle between the concentrations estimated from the two kinds of experiments. 相似文献
16.
《Physics letters. A》2004,324(4):331-336
Based on one-dimensional quantum waveguide theory we study the symmetry of the spin-polarized transmission through an Aharonov–Bohm ring with a magnetic impurity, in which the spin-exchange interaction between an incident electron and the magnetic impurity leads to spin–flip scattering. It shows that for some special Fermi energies, both spin-up and spin-down transmission coefficients are symmetric under the flux reversal in the spin–flip scattering process and the spin-polarized conductance also is symmetric. In above case, AB oscillations of spin-down transmission and reflection are perfectly identical. The effect of the exchange interaction strength and Fermi wave vector on transmission behavior of spin-state electrons is examined. 相似文献
17.
基于一维紧束缚Su-Schrieffer-Heeger模型, 采用分子动力学方法, 讨论了杂质势的强度和杂质之间的距离对电子和空穴极化子动力学性质的影响. 研究结果表明: 1)当杂质势强度保持不变时, 两杂质离子之间的距离(d)在2-16个晶格常数变化时, 电子极化子的平均速度大于空穴极化子的平均速度, 这是由于电子、空穴极化子与杂质势的库仑作用不同而产生的差异, 同时极化子的平均速度随d的增加而增大; 若继续增加杂质离子之间的距离, 电子和空穴极化子的平均速度几乎保持不变, 仅有一些微小的振荡, 这是由于不同距离的杂质离子对电子和空穴极化子产生的势垒或势阱的叠加效果不同而引起的; 2)保持两杂质离子之间的距离不变时, 随着杂质势强度的增大, 电子和空穴极化子的平均速度均减小, 且空穴极化子的平均速度减小趋势更明显. 相似文献
18.
《Superlattices and Microstructures》1998,23(5):985-990
The recombination radiation line of surface excitons and the recombination radiation line of multi-exciton complexes bound to a two-dimensional hole layer are observed in luminescence spectra of [100] silicon metal–oxide–semiconductor structures at low two-dimensional hole density. The circular polarization of these two lines in a transverse magnetic field is defined by the average electron spin. The hole spin contribution to the circular polarization is very small due to Kondo spin correlations of holes in the excitons and complexes and holes in the two-dimensional hole layer. The Coulomb blockade excludes a direct contribution of the complexes to a surface photoconductivity. Moreover, a significant negative photoconductivity of the two-dimensional holes is observed at high excitation levels, presumably as a result of the quantum scattering of the two-dimensional holes by the complexes. A shell model of surface multi-exciton complexes is introduced. 相似文献
19.
A. Phirouznia F. Ghamari 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,74(3):357-362
Non-equilibrium spin accumulation in two-dimensional domain wall (DW) in the presence of external electric field and Rashba
type spin-orbit coupling within the Boltzmann semi-classical
model is investigated. Transport and relaxation of spin polarized current in the DW is governed by spin-flip rates which are
determined by the Rashba interaction and magnetic impurities. Numerical results show that at low impurity densities and nonadiabatic
transport regimes, the Rashba interaction significantly enhances spin polarization of conduction electrons inside the DW. 相似文献
20.
é. G. Batyev 《Journal of Experimental and Theoretical Physics》2010,110(1):88-97
A system of two-dimensional electrons and holes ha s been investigated in a strong magnetic field, when it is sufficient to
take into account only the ground Landau level. It has been shown that the interaction of electrons and holes can lead to
an ordered state. In this problem, the exchange interaction in electron and hole subsystems is significant. The following
two cases have been considered: (a) there are one electron and one hole valleys, and at some magnetic field strength, there
exists an ordered state, as in an excitonic insulator; and (b) there exist one electron and two equivalent hole valleys (as
in the experiment performed by Kvon et al. [1]), and the hole system has an ordered state of the Stoner ferromagnetic type
in a specific range of magnetic field strengths. The spectra of elementary excitations of the Bose and Fermi types have been
obtained. The Fermi excitations have a gap in the energy spectrum, whereas the Bose excitations in the ordered states begin
with zero (to these excitations there corresponds an electric dipole moment). The self-consistent field approximation has
been used, which is exact when the numbers of electrons and holes are equal to each other. 相似文献