Alexander Nazarenko

Antiferromagnetic and van Hove Scenarios for the cuprates: Taking the best of both worlds

A theory for the high temperature superconductors is proposed. The dispersion of carriers in the 2D t-J model is calculated using numerical and analytical techniques, and compared with recent photoemission experimental results that reported a flat dispersion near the X and Y points. Good agreement is observed between theory and experiments. The density of states (DOS) of these dressed quasiparticles has a van Hove singularity. From the two carriers problem in an antiferromagnet, an effective Hamiltonian for holes is proposed. This effective model has superconductivity in the dx2−y2 channel, a critical temperature Tc ∼ 100Kat the optimal hole density, x = 0.15, and a quasiparticle lifetime linearly dependent with energy. The appearance of an optimal concentration is a consequence of the van Hove singularity in the DOS. Other experimental results are also quantitatively reproduced by the theory. The present contribution is based on two recent papers by the authors (Phys. Rev. Lett.73, 728 (1994) and NHMFL preprint, July 1994).

POSSIBLE PHONONIC MECHANISM FOR DX2-Y2 SUPERCONDUCTIVITY IN THE PRESENCE OF SHORT-RANGE ANTIFERROMAGNETIC CORRELATIONS

We discuss the high temperature superconductors in a regime where the antiferromagnetic (AF) correlation length is only a couple of lattice spacings. In the model proposed here, these short-range AF fluctuations play an essential role in the dressing of the carriers, but the attraction needed for superconductivity (SC) arises from a transverse phonon oxygen mode with a finite buckling angle as it appears in

PSEUDOGAP ABOVE TC IN A MODEL WITH DX2-Y2 PAIRING

{\rm YBa_2Cu_3O_{7-\delta}}

One-particle spectral weight of the three-dimensional single-band Hubbard model.

. A simple fermion-phonon model analog to the Holstein model is introduced to account for this effect. We argue that the model has a

Hole dispersion and symmetry of the superconducting order parameter for underdoped CuO2 bilayers and the three-dimensional antiferromagnets.

d_{x^2 - y^2}

Liaison between superconductivity and phase separation

-wave superconducting groundstate. The critical temperature (

Quasiparticle dispersion of Sr2CuO2Cl2

T_c

Superconductivity in the cuprates as a consequence of antiferromagnetism and a large hole density of states

) and the O-isotope effect coefficient (

A simple theory for the cuprates: the antiferro-magnetic van Hove scenario

\alpha_O

Study of arpes data and d-wave superconductivity using electronic models in two dimensions

) vs hole density (