共查询到20条相似文献,搜索用时 15 毫秒
1.
Motivated by experiments in nanoscopic systems, we study a generalized Anderson, which consist of two spin degenerate doublets hybridized to a singlet by the promotion of an electron to two conduction bands, as a function of the energy separation δ between both doublets. For δ=0 or very large, the model is equivalent to a one-level SU(N) Anderson model, with N=4 and 2 respectively. We study the evolution of the spectral density for both doublets (ρ1σ(ω) and ρ2σ(ω)) and their width in the Kondo limit as δ is varied, using the non-crossing approximation (NCA). As δ increases, the peak at the Fermi energy in the spectral density (Kondo peak) splits and the density of the doublet of higher energy ρ2σ(ω) shifts above the Ferrmi energy. The Kondo temperature TK (determined by the half-width at half maximum of the Kondo peak in density of the doublet of lower energy ρ1σ(ω)) decreases dramatically. The variation of TK with δ is reproduced by a simple variational calculation. 相似文献
2.
We investigate theoretically the nonequilibrium transport properties of carbon nanotube quantum dots. Owing to the two-dimensional band structure of graphene, a double orbital degeneracy plays the role of a pseudospin, which is entangled with the spin. Quantum fluctuations between these 4 degrees of freedom result in an SU(4) Kondo effect at low temperatures. This exotic Kondo effect manifests as a four-peak splitting in the nonlinear conductance when an axial magnetic field is applied. 相似文献
3.
The current noise through a mesoscopic quantum dot is calculated and analyzed in the Fermi liquid regime of the SU(N) Kondo model. The results connect the Johnson-Nyquist noise to the shot noise for an arbitrary ratio of voltage and temperature, and show that temperature corrections are sizable in the usual experiments. For the experimentally relevant SU(4) case, quasiparticle interactions are shown to increase the shot noise. 相似文献
4.
Costi TA 《Physical review letters》2000,85(7):1504-1507
The effect of a magnetic field on the spectral density of a S = 1/2 Kondo impurity is investigated at zero and finite temperatures by using Wilson's numerical renormalization group method. A splitting of the total spectral density is found for fields larger than a critical value H(c)(T = 0) approximately 0.5T(K), where T(K) is the Kondo scale. The splitting correlates with a peak in the magnetoresistivity of dilute magnetic alloys which we calculate and compare with the experiments on CexLa1-xAl2,x = 0.0063. The linear magnetoconductance of quantum dots exhibiting the Kondo effect is also calculated. 相似文献
5.
Professor Toshio Soda 《Zeitschrift für Physik B Condensed Matter》1971,13(3):246-267
Using the Coqblin-Schrieffer exchange interaction, we investigate the Kondo effect for a magnetic impurity under the crystalline field, as occuring in La or Y alloys containing cerium impurities. The Hamann typet-matrix equation for the conduction electron scattered by a magnetic impurity is derived and solved, using the method of Zittarz and Müller-Hartmann. We find a Kondo type anomaly and a decreased Kondo temperature due to the crystalline field splittings. The resistivity, entropy and specific heat are calculated and they show some characteristic behavior due to the crystalline field splittings. 相似文献
6.
van der Wiel WG De Franceschi S Elzerman JM Tarucha S Kouwenhoven LP Motohisa J Nakajima F Fukui T 《Physical review letters》2002,88(12):126803
We report a strong Kondo effect (Kondo temperature approximately 4 K) at high magnetic field in a selective area growth semiconductor quantum dot. The Kondo effect is ascribed to a singlet-triplet transition in the ground state of the dot. At the transition, the low-temperature conductance approaches the unitary limit. Away from the transition, for low bias voltages and temperatures, the conductance is sharply reduced. The observed behavior is compared to predictions for a two-stage Kondo effect in quantum dots coupled to single-channel leads. 相似文献
7.
We theoretically study an enhancement of the Kondo effect in quantum dots with two orbitals and spin . The Kondo temperature and conductance are evaluated as functions of energy difference Δ between the orbitals, using the numerical renormalization group method. The Kondo temperature is maximal around the degeneracy point (Δ=0) and decreases with increasing |Δ| following a power law, TK(Δ)=TK(0)(TK(0)/|Δ|)γ, which is consistent with the scaling analysis. The conductance at T=0 is almost constant 2e2/h. Both the orbitals contribute to the conductance around Δ=0, whereas the current through the upper orbital is negligibly small when |Δ|TK(0). These are characteristics of SU(4) Kondo effect. 相似文献
8.
Thermodynamical properties of the “resonance level model” are calculated for arbitrary spin and magnetic field. Assuming this model to describe the basic physics of the Kondo problem we find a satisfactory agreement with recent magnetization data on Fe. 相似文献
9.
Electron tunneling through a double quantum-dot molecule, in the Kondo regime, under the effect of a magnetic field and an applied voltage, is studied. This system possesses a complex response to the applied fields characterized by a tristable solution for the conductance. The different nature of the solutions are studied in and out thermodynamical equilibrium. It is shown that the interdot coupling and the fields can be used to control the region of multistability. The mean-field slave-boson formalism is used to obtain the solution for the problem. 相似文献
10.
Models finite in the one-loop approximation are constructed for quantum field theory. In particular, a finite model with two Higgs multiplets is constructed on the basis of the SU(N) group. Violation of the conditions on the coupling constants induces ultraviolet or infrared-asymptotic finiteness. The behavior of the effective coupling constants in an external gravitational field is also investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 56–64, December, 1991. 相似文献
11.
12.
The effect of an external magnetic field on the ionization equilibrium of atoms in the nondegenerate nonrelativistic plasma
is examined. When taken into account that the interaction of the magnetic moments of electrons with the magnetic field immediately
changes their kinetic energy, which is incorrect, the degree of ionization of atoms will increase with increase in the magnetic
field strength compared to the atomic concentration in the absence of a magnetic field at the same temperature. When taken
into account that this energy changes in view of the Pauli principle and spontaneous minimization of the quantum system, the
degree of ionization must decrease with increase in the external magnetic field strength, that is, a strong magnetic field
suppresses ionization of atoms in the nonrelativistic plasma at a given temperature.
Byelorussian State University; Brest State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No.
7, pp. 36–39, July, 1999. 相似文献
13.
We give asymptotic forms for the high- and low-field magnetic susceptibility for the SU(3) linear dispersion Kondo model for T = 0. The ratio is also calculated for the standard SU(2j + 1) Kondo model for general j. From these results the Wilson number Wj, defined by where χ0 is the zero-temperature zero-field susceptibility, which has been calculated by Andrei and Lowenstein for , is deduced for the SU(3) model j = 1. 相似文献
14.
15.
We study shot noise in the current of quantum dots whose low-energy behavior corresponds to an SU(N) Kondo model, focusing on the case N=4 relevant to carbon nanotube dots. For general N, two-particle Fermi-liquid interactions have two distinct effects: they can enhance the noise via backscattering processes with an N-dependent effective charge, and can also modify the coherent partition noise already present without interactions. For N=4, in contrast with the SU(2) case, interactions enhance shot noise solely through an enhancement of partition noise. This leads to a nontrivial prediction for experiment. 相似文献
16.
R. González-Férez P. Schmelcher 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):189-199
We investigate the effects of a magnetic field with low to intermediate strength on several spectroscopic properties of the
sodium atom. A model potential is used to describe the core of sodium, reducing the study of the system to an effective one-particle
problem. All states with principal quantum numbers n = 3, 4, 5, 6 and 7 are studied and analysed. A grid of twenty values for the field strength in the complete regime B = 0 - 0.02 a.u. is employed. Ionisation energies, transition wavelengths and their dipole oscillator strengths are presented.
Received 5 November 2002 Published online 4 February 2003 相似文献
17.
Tettamanzi GC Verduijn J Lansbergen GP Blaauboer M Calderón MJ Aguado R Rogge S 《Physical review letters》2012,108(4):046803
Semiconductor devices have been scaled to the point that transport can be dominated by only a single dopant atom. As a result, in a Si fin-type field effect transistor Kondo physics can govern transport when one electron is bound to the single dopant. Orbital (valley) degrees of freedom, apart from the standard spin, strongly modify the Kondo effect in such systems. Owing to the small size and the s-like orbital symmetry of the ground state of the dopant, these orbital degrees of freedom do not couple to external magnetic fields which allows us to tune the symmetry of the Kondo effect. Here we study this tunable Kondo effect and demonstrate experimentally a symmetry crossover from an SU(4) ground state to a pure orbital SU(2) ground state as a function of magnetic field. Our claim is supported by theoretical calculations that unambiguously show that the SU(2) symmetric case corresponds to a pure valley Kondo effect of fully polarized electrons. 相似文献
18.
V. M. Polunin P. A. Ryapolov V. B. Platonov E. V. Sheldeshova G. V. Karpova I. M. Aref’ev 《Acoustical Physics》2017,63(4):416-423
Complex measurements of the following elastic-magnetic parameters of a magnetic fluid suspended by magnetic levitation within a horizontal tube in a strong magnetic field were performed: the oscillation frequency and decay coefficient; the static, ponderomotive, and dynamic elasticity coefficients; the fluid displacement under hydrostatic pressure; magnetization curve; and the magnetic field strength and gradient. Calculations based on a model of ponderomotive elasticity with correction for the resistance of a viscous fluid in motion and on the fluid column displacement for two magnetic fluid samples agree well with the experimental magnetization curve. The discussed technique holds promise for research into magnetophoresis and nanoparticle aggregation in magnetic colloids. 相似文献
19.
Jose M. Cervero 《Letters in Mathematical Physics》1984,8(3):233-237
We discuss several field configurations arising from the nonabelian classical field equations of a source-free SU(2)-Yang-Mills system. The quasi-gauge configurations are analyzed and classified according to the solutions of a nonlinear partial-differential equation in two geometrical variables. A comparison is made with the Abelian case, which allows use to assign an electric or magnetic character to these configurations. 相似文献
20.
The coherent-state basis is constructed for symmetric representations of the groups SU(N) and SU(N, 1) and its properties are studied. The evolution of coherent states is considered. A relationship between the SU(N) coherent states and the Glauber coherent states is established.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 83–89, January, 1990. 相似文献