摘要:

Tunneling and point contact spectroscopy show clear phonon features and together with optic measurements give strong support that the electron-phonon interaction (EPI) is large inHTSoxides. Strong correlations inHTSoxides renormalize theEPI(and interaction with impurities) so that the forward scattering peak (FSP) develops for small hole doping&dgr;≪1.TheFSPmechanism explains important properties of the normal and superconducting state. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59646

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The smooth evolution of the tunneling gap ofBi2Sr2CaCu2O8with doping from a pseudogap state in the underdoped cuprates to a superconducting state at optimal and overdoping reflects an underlying SO(6) instability structure of the (&pgr;, 0) saddle points. The pseudogap is probably not associated with superconductivity, but is related to competing nesting instabilities, which are responsible for the stripe phases. We earlier introduced a simpleAnsatzof this competition in terms of a pinned Balseiro-Falicov (pBF) model of competing charge density wave and (s-wave) superconductivity. This model gives a good description of the phase diagram and the tunneling and photoemission spectra. Here, we briefly review these results, and discuss some recent developments: experimental evidence for a non-superconducting component to the pseudogap; and SO(6) generalizations of the pBF model, including flux phase and d-wave superconductivity. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59583

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We have recently begun Monte Carlo simulations of the dynamics of stripe phases in the cuprates. A simple model of spinodal decomposition of the holes allows us to incorporate Coulomb repulsion and coherency strains. We find evidence for a possible stripe disordering transition, at a temperature below the pseudogap onset. Experimental searches for such a transition can provide constraints for models of stripe formation. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59650

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

I discuss the physics of superconductivity and conductivity suppression in Pr-dopedREBa2Cu3O7superconductors, and point out the experiments that indicate Pr(f)-O(p) hybridization as the cause of such suppression. I also show on a qualitative level how the existing experimental facts about this system are described by the hybridization model. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59647

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

An understanding of superconductivity in the holes doped cuprates is formulated as resulting from (i) recovery of superexchange interactions at T(spin-gap), (ii) appearance of a holes clustering instability at the T(pseud-gap), and (iii) virtual spin excitations in the AF background mediating the phase coherence among holes cluster resonances producing Off-Diagonal Long-Range Order. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59584

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We investigate the effect of a ferroelectric transition that is close to a superconducting transition. The closeness of the ferroelectric transition manifests itself in a large ionic dielectric constant &egr;, which is not present in “normal” metals where the conduction electrons shield it out. This reduces the Debye screening parameter fromqDtoqD/&egr;at frequencies below the dispersion frequency&ohgr;t≈20&hthinsp;meVof &egr;(&ohgr;). The electron-phonon matrix element is renormalized as a result. We extend the Eliashberg equations for this renormalized interaction, and develop an algorithm to solve them along the real-&ohgr; axis. We find that various anomalous properties, such as the high value ofTc,the high value of2&Dgr;0/Tc,the d-wave symmetry of the gap parameter, the extended Van-Hove singularity, the damping of the electronic states near the FS, the pseudogap, and various other properties of the cuprates, as well as organic metals, are accounted for. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59648

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Diffraction experiments on the titled compound indicate that theO&dgr;dopants may partially occupy two sites, one of which is coplanar with Hg but does not produce superconductivity, while occupancy of the out-of-plane site does; occupancies of the two configurations cross abruptly near&dgr;=&dgr;2=0.19.The phase diagram, with a plateau inTc(&dgr;),&dgr;1<&dgr;<&dgr;2,rather than the usual parabola, is remarkably similar to that seen in the thermal properties of uncompensated semiconductor impurity bands near the metal-insulator transition, as the author suggested previously. Here the nature of the defects which play the compensating role is identified for other cuprates, in order to explain why the titled compound, alone among the cuprates, has been observed to display “ideal” behavior. Some intrinsic limitations of Rietveld analysis of powder diffraction data for identifying filamentary formation are also discussed, as is the possibility of explaining the data with antiferromagnetic stripe models. Predictions are made for the phase diagram of the superconductive filling factor. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59585

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

An analysis of the electronic specific heat and the thermodynamic critical magnetic field as a function of the temperature is carried out in the cases of gap with isotropic-s, d ands+idsymmetries. While the isotropic-s gap shows an exponential attenuation in the electronic superconducting specific heat for low temperatures(T≪Tc)the d-wave gap presents a quadratic dependence in a wide range of temperatures and goes through a maximum atT<1&hthinsp;K.In the case of thes+idmixing a double peak transition has been obtained from the numerical computations. In theCen(T)/Tdependence a maximum at a certain temperatureT*is obtained which moves to the side of high temperatures when the Fermi level is far away from the van Hove singularity. The temperature dependence of the critical magnetic field presents a great departure from the parabolic law in the case of an isotropic-s gap while in the d-wave case, the mentioned dependence approaches the parabolic one. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59607

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The formation of striped phases in the two-dimensional Hubbard model is investigated within an unrestricted slave-boson approach. We analyze in detail the stability of these structures as a function of doping. It turns out that the inclusion of a long-range Coulomb potential together with the strong local interaction favors the formation of half-filled vertical stripes for doping concentrationsx⩽1/8.Our results show that, besides the underlying lattice structure, also the electronic interactions can contribute to determine the different domain wall textures in Nd doped copper oxides and nickel oxides. An eventual spiral contribution to the striped spin textures in the copper oxide compounds is restricted to the low doping regime according to our calculations. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59651

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The Josephson plasma mode (JPM) in layered cuprate superconductors is strongly affected by the external tunneling injection and/or by the ac field applied. In the model of the c axis tunneling transport, the dielectric function &egr;(&ohgr;) is calculated. For the cases of the tunneling injection and of the microwave, we obtain the conditions when the JPR is shifted and vanishes. It causes the arising of a non-equilibrium instability in respect to the transition into a ferroelectric state characterized by a genuine bias voltage along the c axis of a cuprate superconductor sample that can be observed experimentally. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59608

出版商:AIP    

年代:1999

数据来源: AIP