摘要:

We propose that early speculations on the nature of the normal state of theCuO2planes in highTcsuperconductors can be revised and brought into agreement with more modern theories, simulations and experimental observations. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59578

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Considering both “large-U” and “small-U” orbitals it is found that the high-Tccuprates are characterized by a striped structure, and three types of carriers: polaron-like “stripons” carrying charge, “quasielectrons” carrying charge and spin, and “svivons” carrying spin and lattice distortion. It is shown that this electronic structure leads to the anomalous physical properties of the cuprates, and specifically the systematic behavior of the resistivity, Hall constant, and thermoelectric power. High-Tcpairing results from transitions between pair states of quasielectrons and stripons through the exchange of svivons. A pseudogap phase occurs when pairing takes place above the temperature where stripons become coherent, and this temperature determines the Uemura limit. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59611

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We use a “pairing fluctuation” approach to address the behavior ofTcand pseudogap ind-wave superconductors. This theory yields a BCS-Bose-Einstein crossover description of the superconducting transition, which reduces to BCS in the weak coupling (smallg) limit and to a Bose-Einstein description at largeg. We investigate the effects of quasi-two dimensionality, lattice bandstructure andd-wave symmetry, and obtain a cuprate phase diagram, in quantitative agreement with experiment. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59579

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We calculate the effective interactionWeffbetween two holes added to the ground state of the repulsive three-band Hubbard model. To make contact with Cooper theory and with earlier Hubbard model cluster studies. We first use a perturbative canonical transformation, to generate a two-body Hamiltonian. Then, we extend the results to all orders. The approach is exact in principle, and we obtain a closed analytic expression including explicitly the effects of all virtual transitions to 4-body intermediate states. Our scheme naturally lends itself to embody off-site, inter-planar, phonon-mediated and other interactions which are not considered in the Hubbard model but may well be important. The result depends qualitatively on the symmetry of the two-hole state:1B2and1A2pairs are special, because the bare holes do not interact by the on-site repulsion (W=0pairs). The effective interaction in these channels is attractive and leads to a Cooper-like instability of the Fermi liquid; howeverWeffis repulsive for triplet pairs. Bound two-hole states of the same nature were reported earlier in small cluster calculations by exact diagonalisation methods; only symmetric clusters are good models of the plane. OnceWeffis known, the pair eigenfunction is determined by an integral equation. We present numerical estimates of the binding energy |&Dgr;| of the pairs, which is in the physically interesting range of tens of meV if unscreened on-site repulsion parameters are used. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59625

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We review the explanation for resonant neutron scattering experiments inYBa2Cu3O6+&dgr;andBi2Sr2Ca2O8+&dgr;materials from the point of view of triplet excitation in the particle-particle channel, the &pgr; excitation. Relation of these resonances to the superconducting condensation energy and their role in stabilizing the superconducting state is discussed. Due to the superconducting fluctuations, the &pgr; resonance may appear as a broad peak above Tc. The analogue problem to the &pgr; excitation for the case ofs-wave pairing, the &eegr; excitation, is considered in the strong coupling limit with an emphasis on the resonance precursors in a state with no long range order. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59580

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

It is argued that a new mechanism and many-body theory of superconductivity are required for doped correlated insulators. Here we review the essential features of and the experimental support for such a theory, in which the physics is driven by the kinetic energy. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59581

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We report new types of metallic stripes with ferromagnetic order along the domain walls for the two-dimensional Hubbard model using the dynamical mean-field theory. The (1,0) stripes have the observed filling close to one doped hole per two atoms, while the (1,1) stripes are more extended. The stripe structures are stable at low temperaturesT<70&hthinsp;K,and change into spin spirals at higher temeratures. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59643

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The distribution of charge states of all atoms in the unit cell ofRBa2Cu3Ox;x=6.7&hthinsp;(R=Yb,&hthinsp;Er,&hthinsp;Ho,&hthinsp;Y,&hthinsp;Gd,&hthinsp;Eu,&hthinsp;Sm,&hthinsp;Nd,&hthinsp;Pr)is determined on the basis of comparison of the theoretical calculated electric field gradient tensor and existing experimental data. The variation of the charge states of the atoms as a function of the ionic radius is analyzed. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59644

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Making use of the Bogoliubov-de Gennes equation, we study quasi-particle spectrum and the vortex core structure of a single vortex in quasi 2Ds-wave superconductors for smallpF&xgr;0,wherepFis the Fermi momentum and&xgr;0is the coherence length. During our numerical calculation the electron number is conserved for eachpF&xgr;0.We find that the number of bound states decreases rapidly for decreasingpF&xgr;0.Also we find that the core structure, the current density distribution and the local density of states strongly depend on the value ofpF&xgr;0due to the number and the peak positions of bound states. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59582

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The presence of a normal state spectral (pseudo) gap at the superconducting transition temperature in the underdoped cuprates has important implications for the associated superconducting phase. We argue that this normal state pseudogap derives from pairing fluctuations, which necessarily persist belowTcand which have important implications on the superconducting state. Our Greens function approach, based on the equation of motion method, can be viewed as a natural extension of BCS theory for sufficiently strong pairing interaction, suggested by the short coherence length of the cuprates. In addition to the usual fermionic excitations, there are also incoherent (but not pre-formed) pairs of finite center of mass momentum which must be self consistently incorporated in computingTcand other superconducting properties, such as the superfluid density and the Josephson critical current. Finally, we discuss some of the experimental implications of our theory for the cuprates. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59645

出版商:AIP    

年代:1999

数据来源: AIP