摘要:

AbstractThe electrical resistance of single crystals of the high‐temperature superconductor Tl2Ba2CaCu2O8has been measured as a function of the angle θ between the direction of the magnetic field and the current‐carrying CuO2‐planes. The resistance is maximal for θ = 90° (B⟂CuO2‐planes) and decreases to a minimum at θ = 0°. For small angles an anomalous enhancement of the resistance is found. While the general shape of the resistance is generated by the motion of “pancake vortices” in the CuO2‐planes, the anomaly is due to “Josephson vortices” moving per

ISSN:0003-3804    

DOI:10.1002/andp.19975090302

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractA necessary condition for electron crystallization is the dominance of the electronic Coulomb repulsion as compared with the kinetic energy. We show that 4fsystems are good candidates for electron or hole crystallization to occur since the small radius of the 4fshell leads to small hybridizations and hence kinetic energy of thefelectrons. Crystallization may take place in lattices with several equivalent 4fsites per unit cell when the electron or hole number is less than the number of sites. We give evidence that charge ordering in Yb4As3is an example of the mechanism considered here. We also compare it with those considered by Wigner, Verwey, Mott and Hubbard.

ISSN:0003-3804    

DOI:10.1002/andp.19975090303

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractWe show how the spontaneous bulk, surface and corner magnetizations in the square lattice Ising model can all be obtained within one approach. The method is based on functional equations which follow from the properties of corner transfer matrices and vertex operators and which can be derived graphically. In all cases, exact analytical expressions for general anisotropy are obtained. Known results, including several for which only numerical computation was previously possible, are verified and new results related to general anisotropy and corner angles are obtained.

ISSN:0003-3804    

DOI:10.1002/andp.19975090304

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractWe study the problem of the phonon‐induced electron‐electron interaction in a solid. Starting with a Hamiltonian that contains an electron‐phonon interaction, we perform a similarity renormalization transformation to calculate an effective Hamiltonian. Using this transformation singularities due to degeneracies are avoided explicitly. The effective interactions are calculated to second order in the electronphonon coupling. It is shown that the effective interaction between two electrons forming a Cooper pair is attractive in the whole parameter space. For a simple Einstein model we calculate the renormalization of the electronic energies and the critical temperature of superconduct

ISSN:0003-3804    

DOI:10.1002/andp.19975090305

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractDuring the thermal evolution of the universe, symmetry of the vacuum state in the presence of quantum fields should have changed at various stages. A possible indication of this effect on the DFSZ invisible axion model of the Peccei‐Quinn CP conserving mechanism is presented here. To start with, the background theory of this mechanism in the cosmic evolution has been fully reviewed, as well as the leading cosmological arguments setting limits on the mass and coupling of such a particle. The CP conserving lagrangian of the invisible axion model also includes instanton gauge field configurations. In our opinion, these configurations could behave non trivially while decreasing the temperature as a consequence of the vacuum symmetry modifications. The interplay between symmetry modifications and cosmic evolution may thus lead to yet unclear effects. In fact, the model considered here is really quite a baby version of the real world, so that only preliminary indications and bare consistency arguments have been done from it. Nevertheless, the underlying idea, a possible neutral Higgs fields approximate resonance condition, seems to survive even in more sophisticated model

ISSN:0003-3804    

DOI:10.1002/andp.19975090306

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

ISSN:0003-3804    

DOI:10.1002/andp.19975090301

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY