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941.
The ground state properties of CeCoPO, a homologue of the new high temperature superconductors LnFePnO1-xFx, were studied by means of susceptibility, specific heat, and resistivity measurements on polycrystals. The observation of a well defined Curie-Weiss behavior above 230 K with μeff=2.9μB and a ferromagnetic ordering below is similar to what was observed in LaCoPO and points to magnetism of the Co-3d electrons. However, the Ce-ions are on the border to magnetism with a Kondo scale of and show an enhanced Sommerfeld coefficient of . 相似文献
942.
E. Kerscher M.T. Kelemen K.H. Diefenbach O. Stockert H. v. Löhneysen E. Dormann 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):241-247
Single-crystal like nuclear magnetic resonance spin-echo spectra are obtained for powder samples of the antiferromagnet CeCu5Au in the paramagnetic phase. Line shifts and quadrupolar splittings are analyzed for 63Cu and 65Cu. The influence of the extreme magnetic anisotropy of the CeCu6-xAux compounds on nuclear spin relaxation is discussed.
Received 19 June 2000 相似文献
943.
L.A. Errico M. Rentería A.F. Pasquevich A.G. Bibiloni K. Freitag 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(2):149-156
The time-differential-perturbed γ-γ angular-correlation technique (TDPAC) with ion-implanted 181Hf tracers has been applied to study the hyperfine interactions of 181Ta impurities in the cubic bixbyite structure of Er
2
O
3
and Gd
2
O
3
. The TDPAC experiments were performed in air in the temperature range 300-1073 K (in the case of Er
2
O
3
) and 300-1173 K (in the case of Gd
2
O
3
). Three electrical-quadrupole interactions were found in each oxide in the whole studied temperature range. Two of them were
attributed to the electric-field gradients (EFG) acting on 181Ta probes substitutionally located on the two nonequivalent free-of-defects cation sites of the bixbyite structure. The EFG
results are compared with predictions of the point-charge model and discussed together with previous results obtained with
the probes 111Cd and 181Ta in other isomorphous sesquioxides. The temperature dependence of the hyperfine parameters for both oxides is also discussed
in terms of dilatometric expansion data.
Received 29 December 2000 and Received in final form 8 March 2001 相似文献
944.
945.
946.
Simultaneous effects of an on-center hydrogenic impurity and band edge non-parabolicity on intersubband optical absorption coefficients and refractive index changes of a typical GaAs/Al x Ga 1 x As spherical quantum dot are theoretically investigated,using the Luttinger-Kohn effective mass equation.So,electronic structure and optical properties of the system are studied by means of the matrix diagonalization technique and compact density matrix approach,respectively.Finally,effects of an impurity,band edge non-parabolicity,incident light intensity and the dot size on the linear,the third-order nonlinear and the total optical absorption coefficients and refractive index changes are investigated.Our results indicate that,the magnitudes of these optical quantities increase and their peaks shift to higher energies as the influences of the impurity and the band edge non-parabolicity are considered.Moreover,incident light intensity and the dot size have considerable effects on the optical absorption coefficients and refractive index changes. 相似文献
947.
Simultaneous effects of conduction band non-parabolicity and hydrostatic pressure on the binding energies of 1S, 2S, and 2P states along with diamagnetic susceptibility of an on-center hydrogenic impurity confined in typical GaAs/AlxGa1-xAs spherical quantum dots are theoretically investigated using the matrix diagonalization method. In this regard, the effect of band non-parabolicity has been performed using the Luttinger-Kohn effective mass equation. The binding energies and the diamagnetic susceptibility of the hydrogenic impurity are computed as a function of the dot radius and different values of the pressure in the presence of conduction band non-parabolicity effect. The results we arrived at are as follows: the incorporation of the band edge non-parabolicity increases the binding energies and decreases the absolute value of the diamagnetic susceptibility for a given pressure and radius; the binding energies increase and the magnitude of the diamagnetic susceptibility reduces with increasing pressure. 相似文献
948.
We investigate the ground-state properties of the Anderson singleimpurity model (finite Coulomb impurity repulsion) with the Coupled ClusterMethod. We consider different CCM reference states and approximation schemes and make comparison with exact Green's function results for the non-interacting model and with Brillouin-Wigner perturbation theory for the full interacting model. Our results show that coupled cluster techniques are well suited to quantum impurity problems. 相似文献
949.
Kondo transport properties through a Kondo-type quantum dot (QD) with a side-coupled triple-QD structure are systematically investigated by using the non-equilibrium Green's function method. We firstly derive the formulae of the current, the linear conductance, the transmission coefficient, and the local density of states. Then we carry out the analytical and numerical studies and some universal conductance properties are obtained. It is shown that the number of the conductance valleys is intrinsically determined by the side-coupled QDs and at most equal to the number of the QDs included in theside-coupled structure in the asymmetric limit. In the process of forming the conductance valleys, the side-coupled QD system plays the dominant role while the couplings between the Kondo-type QD and the side-coupled structure play the subsidiary and indispensable roles. To testify the validity of the universal conductance properties, another different kinds of side-coupled triple-QD structures are considered. It should be emphasized that these universal properties are applicable in understanding this kind of systems with arbitrary many-QD side structures. 相似文献
950.
Magnetotransport through an Aharonov-Bohm ring with parallel double quantum dots coupled to ferromagnetic leads 下载免费PDF全文
Using the Keldysh nonequilibrium Green function and equation-of-motion
technique, this paper studies the magnetotransport through an Aharonov--Bohm (AB) ring with
parallel double quantum dots coupled to ferromagnetic leads. It calculates
the transmission probability in both the equilibrium and the nonequilibrium
case, analyses the conductance and the tunnel magnetoresistance for
various parameters, and obtains some new results. These results show that this
system is provided with an excellent spin filtering property, and that a large
tunnelling magnetoresistance and a negative tunnelling magnetoresistance can arise
by adjusting relative parameters; these facts indicate that this system is a
possible candidate for spin valve transistors, and has important
applications in spintronics. 相似文献