Non-Kondo mechanism for resistivity minimum in spin ice conduction systems

We present a mechanism of resistivity minimum in conduction electron systems coupled with localized moments, which is distinguished from the Kondo effect. Instead of the spin-flip process in the Kondo effect, electrons are elastically scattered by local spin correlations which evolve in a particular way under geometrical frustration as decreasing temperature. This is demonstrated by the cellular dynamical mean-field theory for a spin-ice-type Kondo lattice model on a pyrochlore lattice. Peculiar temperature dependences of the resistivity, specific heat, and magnetic susceptibility in the non-Kondo mechanism are compared with the experimental data in metallic Ir pyrochlore oxides.     

Spin-resolved splitting of Kondo resonances in the presence of RKKY-type coupling

We have performed spin-resolved measurements on a Kondo impurity in the presence of RKKY-type exchange coupling. By placing manganese phthalocyanine (MnPc) molecules on Fe-supported Pb islands, a Kondo system is devised which is exchange coupled to a magnetic substrate via conduction electrons in Pb, inducing spin splitting of the Kondo resonance. The spin-polarized nature of the split Kondo resonance and a spin filter effect induced by spin-flip inelastic electron tunneling are revealed by spin-polarized scanning tunneling microscopy and spectroscopy.     

Korringa relaxation time of magnetic ion system near a two-dimensional electron gas

Spin relaxation of Mn ions in a (Cd,Mn)Te quantum well with quasi-two-dimensional carriers (Q2DEG) is investigated. The mechanism of energy transfer is spin-flip scattering of Mn spin with electrons making transitions between spin subbands accompanied by a change in the Mn spin. A calculation of the spin-flip scattering rate shows that the Mn spin relaxation rate is proportional to the coupling constant squared, the density of states squared, and the electron temperature, the so called Korringa relaxation rate. It was found that for small Mn ion concentration, the relaxation time ≈10−7-10−6s is in a good agreement with experimental results. Moreover, the relaxation rate scales with L⁻², L being the well width, and it can be enhanced over its value in bulk.     

Anti-resonance and the “0.7 anomaly” in conductance through a quantum point contact

We investigate the transmission of electrons through a quantum point contact by using a quasi-one-dimensional model with an extra local bound state staying below the band bottom. While the complete transmission in lower channels gives rise to plateaus of conductance at multiples of 2e²/h, the electrons in the lowest channel are scattered by the local bound state when it is singly occupied. This scattering produces a wide anti-resonant zero-transmittance for singlet formed by tunneling and local electrons, and has no effect on triplets, leading to an exact 0.75(2e²/h) shoulder prior to the first 2e²/h plateau. While at low temperature, the formation of Kondo cloud screens magnetic moment of the local bound state and reduces the scattering to the singlet channel, complementing the shoulder from 0.75 to 1.     

Scattering of spin-polarized electron in an Aharonov-Bohm potential

The scattering of spin-polarized electrons in an Aharonov-Bohm vector potential is considered. We solve the Pauli equation in 3 + 1 dimensions taking into account explicitly the interaction between the three-dimensional spin magnetic moment of electron and magnetic field. Expressions for the scattering amplitude and the cross section are obtained for spin-polarized electron scattered off a flux tube of small radius. It is also shown that bound electron states cannot occur in this quantum system. The scattering problem for the model of a flux tube of zero radius in the Born approximation is briefly discussed.     

Kondo state of Co impurities at noble metal surfaces

We use scanning tunneling microscopy and spectroscopy to study the properties of magnetic Co adatoms on noble metal surfaces at 6 K. Due to spin-flip scattering of the substrate electrons at the impurity the many-body Kondo state forms. This state is characterized by an energy, the Kondo temperature T_K. We measure T_K of adatom systems and a resonant scattering phase shift locally and are thus able to discuss the coupling of the Co adatom to the metal electronic system. From the resonant scattering phase shift of the surface-state electrons scattering off a Co adatom on Ag(111), we find that the coupling to the surface state is rather weak. On the other hand, increasing the number of nearest neighbor substrate atoms increases the coupling of a Co adatom to the host metal and increases T_K. This shows the dominant character of the coupling of the Co atom to the bulk states of the substrate crystal. PACS 72.10.Fk; 68.37,Ef; 72.15.Qm     

Electromagnetic scattering by a time reversal symmetry broken topological insulator sphere

An exact solution of electromagnetic wave scattering by a time reversal symmetry broken topological insulator sphere is researched. According to the constitute relations of topological insulator, we modified magnetic vector potential and electric vector potential of standard Mie theory and derived scattered electromagnetic fields and scattered coefficients. Numerical results show that, when the time reversal symmetry is broken, the extinction efficiencies and the scattering efficiencies are influenced by topological magneto-electric polarizability.     

Nonequilibrium Kondo effect and Andreev reflection through double quantum dots with spin-flip scattering

The Kondo effect and the Andreev reflection tunneling through a normal (ferromagnet)-double quantum dots-superconductor hybrid system is examined in the low temperature by using the nonequilibrium Green's function technique in combination with the slave-boson mean-field theory. The interplay of the Kondo physics and the Andreev bound state physics can be controlled by varying the interdot hopping strength. The Andreev differential conductance is mainly determined by the competition between Kondo states and Andreev states. The spin-polarization of the ferromagnetic electrode increases the zero-bias Kondo peak. The spin-flip scattering influences the Kondo effect and the Andreev reflection in a nontrivial way. For the ferromagnetic electrode with sufficiently large spin polarization, the negative Andreev differential conductance is found when the spin flip strength in the double quantum dots is sufficiently strong.     

Spectroscopy of soft modes and quantum phase transitions in coupled electron bilayers

Strongly correlated two-dimensional electrons in coupled semiconductor bilayers display remarkable broken symmetry many-body states under accessible and controllable experimental conditions. In the case of continuous quantum phase transitions (QPTs), soft collective modes drive the transformations that link distinct ground states of the electron double layers. In this paper we consider results showing that resonant inelastic light scattering methods detect soft collective modes of the double layers and probe their evolution with temperature and magnetic field. The light scattering experiments offer venues of research of fundamental interactions and continuous QPTs in low-dimensional electron liquids.     

Instability of Non—Fermi Liquid Behavior in the Two—Channel Kondo Model

The effects of interchannel scattering of conduction electrons by the impurity and repulsion of conduction electrons at the impurity site on the two-channel Kondo model are simultaneously considered in this paper,It is shown that these two perturbations will substantially modify the usual local non-Fermi liquid behavior of the two-channel Kondo model.With bosonization and unitary transformations we find that the system can be transformed into a single channel Kondo model with anisotropy between longitudinal and transverse exchange couplings,Whatever for originally antiferromagnetic or ferromagnetic isotropic coupling,the system always flows to strong-coupling limit,which exhibits local Fermi liquid behavior at low temperatures.     

Transport through a quantum dot subject to spin and charge bias

Spin and charge transport through a quantum dot coupled to external nonmagnetic leads is analyzed theoretically in terms of the non-equilibrium Green function formalism based on the equation of motion method. The dot is assumed to be subject to spin and charge bias, and the considerations are focused on the Kondo effect in spin and charge transport. It is shown that the differential spin conductance as a function of spin bias reveals a typical zero-bias Kondo anomaly which becomes split when either magnetic field or charge bias are applied. Significantly different behavior is found for mixed charge/spin conductance. The influence of electron-phonon coupling in the dot on tunneling current as well as on both spin and charge conductance is also analyzed.     

Spin-flip scattering of conduction electrons by dislocations in a metal

The spin-flip scattering of conduction electrons by dislocations in metals with a strong spin-orbit coupling is considered. Calculations are performed in terms of the model spin-orbit potential describing the spin-flip scattering of conduction electrons. It is shown that deformation of the crystal lattice in a metal leads to a change in the structure factor. The core of a rectilinear edge dislocation is calculated by the molecular dynamics method. The results obtained are compared with the experimental data on conduction-electron spin resonance (CESR) in copper.     

Correlation between the residual resistivity and the temperature resistance minimum in amorphous alloys

A simple formula for the correlation between the residual resistivity and the temperature resistivity minimum in amorphous transition metal-metalloid alloys is derived by means of the Ziman potential scattering theory and the Kondo spin-flip scattering theory.The author would like to thank Dr.O.Hudak for helpful discussions.     

Beam radiated from quasi-homogeneous uniformly polarized electromagnetic source scattering on quasi-homogeneous media

We study the coherence properties of the field generated by beam radiated from quasi-homogeneous (QH) electromagnetic source scattering on QH media. Formulas for the spectral density and spectral degree of coherence of the three dimensional scattered field are derived. The results show under assumption that the diagonal correlation coefficients of the source are proportional to each other, the far field of the scattered light satisfy two reciprocity relations analogous to that in the scalar case, that, the spectral density is proportional to the convolution of the spectral density of the source and the spatial Fourier transform of the correlation coefficient of the scattering potential; the spectral degree of coherence is proportional to the convolution of the diagonal correlation coefficients and the strength of the scattering potential.     

The interplay of thermal and pump fluctuations in stimulated Brillouin scattering

We present a experimental and theoretical investigation of spontaneously initiated stimulated Brillouin scattering in which the interplay of two independent noise sources (thermal and pump) can be studied by controlling the relative importance of each source. We vary the pump noise by adding a controlled amount of Gaussian noise to the input pulses, and we control the contribution of the thermal noise by examining the energy statistics of both entire scattered pulses and of temporal slices of the scattered pulses. We show that the energy of the whole Stokes pulses follow a Gaussian distribution but that the energy of the Stokes pulse slices do not.     

Polarized angular dependence of out-of-plane light-scattering measurements for nanoparticles on wafer

Bidirectional ellipsometry has been developed as a technique for distinguishing among various scattering features near surfaces. The polarized angular dependence of out-of-plane light-scattering by the nanoparticles on wafer is calculated and measured according to Rayleigh limit. These calculations and measurements yield angular dependence of bidirectional ellipsometric parameters for out-of-plane scattering. The experimental data show good agreement with theoretical predictions for different diameter of nanoparticles. The results suggest that improvements for accuracy are possible to perform measurements of scattering features from nanoparticles. The angular dependence and the polarization of light scattered by nanoparticles can be used to determine the size of nanoparticulate contaminants on silicon wafers.     

Rate of energy loss to intravalley acoustic modes in a degenerate surface layer at low lattice temperatures

The rate of loss of the energy of non-equilibrium electrons due to inelastic interaction with intravalley acoustic phonons in a degenerate surface layer is calculated for low temperatures when the approximations of the well-known traditional theory are not valid. The loss characteristics for GaAs and Si seem to be significantly different compared to what follows from the traditional approximations.     

Penetration range and backscattering ratio of low-energy electrons in metals

The accuracy of the Ashley's optical-data model [J.C. Ashley, J. Electron Spectrosc. Relat. Phenom. 50 (1990) 323] for describing the energy loss rate and inelastic mean free path of low-energy electrons in Al and Cu has been examined through the use of Ashley's model for calculating the electron penetration range. The latter has also been calculated using the empirical expressions reported by Iskef et al. [Phys. Med. Biol. 28 (1983) 535] and Gryzinski excitation function. The resulting range of penetration is used for determining the electron backscattering coefficients via the use of Vicanek and Urbassek theory [Phys. Rev. B 44 (1991) 7234] where the transport cross-sections are obtained from Rouabah et al. [Appl. Surf. Sci. 255 (2009) 6217] approximation. Besides the electron backscattering coefficients have been calculated from Monte Carlo simulation in which the inelastic scattering processes are handled using Ashley dielectric approach. It is found that the use of Ashley's optical model via Monte-Carlo method gives backscattering coefficients more accurate than those obtained via Vicanek and Urbassek theory. This confirms the accuracy of Ashley's optical model and shows that the Monte-Carlo method is much more accurate and precise than the Vicanek and Urbassek semi-empirical approach.     

Low-temperature transport properties of individual SnO2 nanowires

Stannic oxide (SnO₂) nanowires have been prepared by Chemical vapor deposition (CVD). The low-temperature transport properties of a single SnO₂ nanowire have been studied. It is found that the transport of the electrons in the nanowires is dominated by the Efros-Shklovskii variable-range hopping (ES-VRH) process due to the enhanced Coulomb interaction in this semiconducting nanowire. The temperature dependence of the resistance follows the relation lnR∼T^−1/2. On the I-V and dI/dV curves of the nanowire a Coulomb gap-like structure at low temperatures appears.