Screening and interaction of magnetic impurities in Luttinger liquids

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.     

Interactions between a 3d impurity and conduction electrons

We calculate the effective interaction between a 3d impurity and conduction electrons resulting from an Anderson mixing interaction taken to second order. The orbital state of the impurity in the crystal field is taken into account. The results, which are tabulated in detail, exhibit coupling of the conduction electrons to the impurity's orbital degrees of freedom as well as to its spin.     

Nuclear and ion spins in semiconductor nanostructures

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.     

Phase Transition of the Isotropic Kondo Hamiltonian:A "Luttinger-Liquid" Description

Analysis of the bosonized Kondo Hamiltonian at zero temperature shows that the interaction between the conduction electrons via a magnetic impurity scattering induces nonlinear couplings between its elementary excitations, which may be described by an effective "Luttinger-liquid". With the Bogoliubov transformation, the corresponding ground-state wave function is obtained. In particular, we are able to treat infrared divergencea led by the strong effective interactions between the conduction electrons for the long wavelength part directly and investigate the nontrivial ferromagnetic-antiferromagnetic transition of the impurity spin. Comparison with the previous studies is also given.     

Abelian Bosonization Approach,to a Magnetic Impurity Model

Abelian bosonization is applied to a magnetic impurity model, the so-called Wolff impurity model. The resulting bosonized version of the model can be solved exactly. We calculate the local dynamic spin and charge density-density correlations of the conduction electrons, and show that a quasi-particle peak in the spin-density excitations appears and becomes sharp significantly as the local interaction U grows up. The local static spin and charge susceptibilities and specific heat of the interacting electrons are also obtained, explicitly displaying a local Fermi liquid behavior.     

Rashba coupling induced spin accumulation in two-dimensional domain wall

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.     

Hyperfine fields in 3d impurities in metals

The dynamic spin polarization of conduction electrons by an impurity spin is shown to provide a significant positive contribution to the impurity hyperfine field, accounting for the fact that the hyperfine field per unit impurity spin is only about half as large for impurities in metals as in insulators. The anomalously small hyperfine fields of Fe impurities in the noble metals are found to result from an orbital contribution. Quantitative analysis of this orbital contribution suggests that a strong dynamic Jahn-Teller effect is present. Similar orbital contributions can yield a strongly anisotropic hyperfine field for Fe or Cr impurities in hexagonal host metals, depending on the type of crystal-field orbital ground state.     

Origin of magnetic anisotropy of Gd metal

Using first-principles theory, we have calculated the energy of Gd as a function of spin direction, theta, between the c and a axes and found good agreement with experiment for both the total magnetic anisotropy energy and its angular dependence. The calculated low temperature direction of the magnetic moment lies at an angle of 20 degrees to the c axis. The calculated magnetic anisotropy energy of Gd metal is due to a unique mechanism involving a contribution of 7.5 microeV from the classical dipole-dipole interaction between spins plus a contribution of 16 microeV due to the spin-orbit interaction of the conduction electrons. The 4f spin polarizes the conduction electrons via exchange interaction, which transfers the magnetic anisotropy of the conduction electrons to the 4f spin.     

Optically probing the fine structure of a single Mn atom in an InAs quantum dot

We report on the optical spectroscopy of a single InAs/GaAs quantum dot doped with a single Mn atom in a longitudinal magnetic field of a few Tesla. Our findings show that the Mn impurity is a neutral acceptor state A0 whose effective spin J=1 is significantly perturbed by the quantum dot potential and its associated strain field. The spin interaction with photocarriers injected in the quantum dot is shown to be ferromagnetic for holes, with an effective coupling constant of a few hundreds of mueV, but vanishingly small for electrons.     

Characterizing a high spin magnetic impurity via Andreev reflection spectroscopy

The ground state properties of a high spin magnetic impurity and its interaction with an electronic spin are probed via Andreev reflection. We see that through the charge and spin conductance one can effectively estimate the interaction strength, the ground state spin and magnetic moment of any high spin magnetic impurity. We show how a high spin magnetic impurity at the junction between a normal metal and superconductor can contribute to superconducting spintronics applications. Particularly, while spin conductance is absent below the gap for Ferromagnet-Insulator-Superconductor junctions we show that in the case of a Normal metal-High spin magnetic impurity-Normal Metal-Insulator-Superconductor (NMNIS) junction it is present. Further, it is seen that pure spin conduction can exist without any accompanying charge conduction in the NMNIS junction.     

Theory of the transition at 0.2 K in Ni-doped Bi2Sr2CaCu2O8

A theory is put forward that the electronic phase transition at 0.2 K in Ni-doped Bi2Sr2CaCu2O8 is a result of the formation of a spin density wave in the system of Ni impurities. The driving force for the transition is the exchange interaction between the impurity spins and the spins of the conduction electrons. This creates a small gap at two of the four nodes of the superconducting gap. The effect is to reduce the thermal conductivity by a factor of 2, as observed.     

Superconductivity of spin glasses

The coexistence of superconducting and spin glass phases is investigated. The dependence of the phase transition temperature in the spin glass state both on the impurity concentration and the superconductivity state is given. The influence of the spin glass phase on the renormalized frequency and the order parameter of the conduction electrons is determined.     

Collective state of electrons and impurities with a spin

The problem of states of an electron system interacting with impurities that have a spin of 1/2 is considered. It is shown that in the calculation of the energy of the system, the electron spin-flip processes and the formation of electron–hole–impurity flip spin (hole against the background of electrons with another spin projection) play the major role. Such complexes are accumulated in the system (a sort of Bose condensate of complexes is formed); this reduces the energy of the system, which is a linear function of the initial interaction of an electron with the impurity spin (in contrast, for example, to the result obtained in perturbation theory). The hole-type excitation and the spin excitation have a gap in the spectrum. Small parameters of the problem are the interaction of electrons with impurity spins and the number of impurities. The electron–electron interaction is not taken into account. Impurities are assumed to be distributed at random, and calculations are performed using the known averaging over the positions of impurities.     

The Fano antiresonance effect in the current-voltage characteristics of a nanostructure with a single magnetic impurity

A theoretical investigation is performed of quantum coherent electron transport through a nanostructure that contains an impurity ion with an uncompensated magnetic moment. It is shown that the transmission coefficient of spin-polarized electrons has the Fano antiresonance. This effect appears as a result of exchange interaction between the spin of transmitted electron and the spin of impurity ion. It is shown that Fano antiresonance leads to a qualitative modification of the current-voltage characteristic of the structure responsible for the large value of magnetoresistance.     

Optical polarization of nuclei and ODNMR in GaAs/AlGaAs quantum wells

Optical orientation of electrons was used to polarize the crystal lattice nuclei in quantum-size heterostructures and to study the effect of the conduction band spin splitting on the spin states of quasi-two-dimensional (2D) electrons drifting in an external electric field. High (～1%) nuclear polarization was registered using polarized luminescence and ODNMR in single GaAs/AlGaAs quantum wells. Measurement was made of the hyperfine interaction fields created by polarized nuclei on electrons and by electrons on nuclei. The spin-lattice relaxation of nuclei on the non-degenerate 2D electron gas was calculated. A comparison of the theoretical and experimental longitudinal relaxation times permitted the conclusion that the localized charge carriers are responsible for nuclear polarization in quantum wells in the temperature range of 2–77 K. A new effect has been studied, i.e. induction of an effective magnetic field acting on 2D electron spins when electrons drift in an external electric field in the quantum well plane. This effective field B_eff is due to the spin splitting of the conduction band of 2D electrons. The paper discusses possible registration of an ODNMR signal when the field B_eff is modulated by an electric current during optical orientation.     

Strong coupling in the Kondo problem in the low-temperature region

The magnetic field dependence of the average spin of a localized electron coupled to conduction electrons with an antiferromangetic exchange interaction is found for the ground state. In the magnetic field range μH∼0.5T _c (T _c is the Kondo temperature) there is an inflection point, and in the strong magnetic field range μH≫T _c , the correction to the average spin is proportional to (T _c /μ H)². In zero magnetic field, the interaction with conduction electrons also leads to the splitting of doubly degenerate spin impurity states. Zh. éksp. Teor. Fiz. 115, 1263–1284 (April 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor     

Anomalous Spin Textures in a 2D Topological Superconductor Induced by Point Impurities

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.     

Spin cloud induced around an elastic scatterer by the intrinsic spin hall effect

Similar to the Landauer electric dipole created around an impurity by the electric current, a spin polarized cloud of electrons can be induced by the intrinsic spin Hall effect near a spin independent elastic scatterer. It is shown that in the ballistic range around the impurity, such a cloud appears in the case of Rashba spin-orbit interaction, even though the bulk spin Hall current is absent.     

Mechanisms of spin-polarized current-driven magnetization switching

The mechanisms of the magnetization switching of magnetic multilayers driven by a current are studied by including exchange interaction between local moments and spin accumulation of conduction electrons. It is found that this exchange interaction leads to two additional terms in the Landau-Lifshitz-Gilbert equation: an effective field and a spin torque. Both terms are proportional to the transverse spin accumulation and have comparable magnitudes.     

一维自旋1/2电子系统的单杂质散射研究

应用高斯波泛函方法，研究了单个局域杂质对一维自旋1/2传导电子的散射问题．研究结果表明，双粒子散射与单粒子散射具有同样的重要性．由于这两种散射机制相互竞争，形成了拉亭格液体中电荷密度波和自旋密度波的各自的重整化质量．随着这些质量的消失，在参量空间中出现了相界，在不同相区中系统呈现不同的动力学行为 关键词：