Search

The crystalline-electric-field parameters Anm for RFe11Ti and RFe11TiH (R=Sm, Tb, Ho) are evaluated by fitting calculations to the magnetization curves measured on the single crystals or on magnetically aligned powder samples at 4.2K and higher temperatures. Interstitial hydrogen atom in RFe11Ti has been found to have a significant effect on crystalline-electric-field parameters Anm. By using the parameters of exchange field 2μBHex estimated from inelastic neutron scattering experiments and the fitted Anm, the calculations can reproduce the experimental curves well.

In this paper, we try to present a way in terms of which one can analytically obtain the Hartree self-consistent potential instead of computing it by the numerical iterative procedure as usual, which is convenient for us to describe the current flow through a mesoscopic conductor. In our treatment, we expand the action function S(x) by Planck constant , then the self-consistent potential and the wavefunction can be solved analytically order by order starting from the Poisson equation and quantum Hamilton–Jacobian equation, the differential conductance and quantum capacitance can thus be obtained naturally. In our paper, we show the quantum corrections up to the second order, and the electron-electron interaction is considered only at the Hartree approximation level.

A quantum field theory for the η pairing mechanism of a Hubbard model within the mean-field framework is presented in this letter. It is found that the energy spectrum has two separate branches, and the eigenfunction has a plane-wave type. This result differs from the discrete lattice case in momentum space.

A new mechanism for the pairing in cuprate superconductors is proposed and studied by using the mean-field approximations. A hybridization singlet pair is formed by media of strong hybridization between a d hole on Cu site and a p doped hole with opposite spin on the nearest-neighbor O site in the CuO2 plane. The transition temperature can be found to reach a peak around δ ~ 0.1-0.3 and the ratio of energy gap to Tc has a maximum 4.0. This is in good agreement with experiments. The specific heat jump as a function of doping fraction δ, the upper critical field and the coherence length, are obtained.

The properties in the spin-bag mechanism of hige Tc superconductivity are studied in the SDW background. It is found that if the Coulomb repulsive potential is much smaller than the valence-band width and is not beyond a particular range determined by the bag energy, two doped holes can be pairing via sharing a common bag. The transition temperature has a maximum value of the order 200 K for reasonable parameters but is independent of doping concentration. In addition, the ratio of the energy gap to Tc is found to be the same as the BCS value. Finally, the specific heat jump at the transition temperature, the coherence length and the upper critical field are roughly estimated.

In this paper a general approach to obtaining the statistical distribution function is given. In the specific case of free field, the statistical distribution functions are derived under a basis set of general commutation relations by using the double–time Green's functions in the first, second and third order decoupling approximations respectively.

The thermodynamic properties of superconducting state in BZA mean-field theory of RVB superconducting mechanism are evaluated in this letter.