ORAL SESSION 1A1: HTS Theory I

Monday, Feb. 21, 4:30 p.m. –6:30 p.m., Room 303A (GRB)

Chairs: D. Scalapino (U California-Santa Barbara), B. Chakraverty (LEPES/CNRS-Grenoble)

1A1.1 Are Spin and Charge Really Separated in HTS? - Comparison between Theory and Experiment -

Sadamichi Maekawa and Takami Tohyama, Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

Presenting Author: S. Maekawa

Recently, it has been directly observed that, in one-dimensional cuprates, the electronic excitations are not quasi-particles with spin 1/2 and charge e, but are decoupled collective modes of spin and charge excitations called spinons and holons.

Here, we extend the study to the two-dimensional insulating cuprates. By using the numerically exact diagonalization technique, we obtain that the spin and charge separation occurs at least approximately around a doped hole with momentum k = (p ,0)-(p /2,p /2) in the two-dimensional insulating cuprates, where a novel spin-liquid state is realized, although the ground state is the Neel state. We find the d-wave-like dispersion in the (p ,0)-(p /2,p /2) direction. This explains the recent angle-resolved photoemission experiment in Ca₂CuO₂Cl₂ by Ronning et al. The systematics in the electronic excitations from insulating to underdoped HTS cuprates are discussed.

1A1.2 Quantum Protectorates in the Cuprate Superconductors

David Pines, Institute for Complex Adaptive Matter, University of California Office of the President, LANSCE Division, Los Alamos National Laboratory, and Science and Technology Center for Superconductivity, University of Illinois

Presenting Author: D. Pines

Following the identification of the pairing state, the major challenge in understanding the cuprate superconductors has been determining the evolution with doping and temperature of their anomalous normal state behavior. Key to this understanding is the experimentally determined magnetic phase diagram for the cuprates, which provides us with information on the protected magnetic properties of the normal state, generic behavior that is reliably the same one system to the next, regardless of details. I discuss candidate quantum protectorates and the status of microscopic model calculations, with particular attention to anisotropic quasiparticle behavior in the magnetically underdoped cuprates where mesoscopic ordering plays an as yet undetermined role.

1A1.4 Understanding HTS Cuprates on the Basis of Phase String Theory of Doped Anti-ferromagnet

C.S. Ting, Z.Y. Weng, and D.N. Sheng, Department of Physics and Texas Center for Superconductivity, University of Houston, Houston, TX 77004

Presenting Author: C.S. Ting

Based upon the bosonic RVB mean field description of the t-J model including the phase string field effect, we numerically investigated several of the magnetic properties for this model. Our results are in good agreement with the neutron scattering data and NMR relaxation rates measured for both underdoped and optimum doped cuprates. The superconductivity in this model has a d-wave symmetry and is non-BCS like. Some of its features will be discussed. We also studied the motion of a single hole in a half-filled bosonic RVB background. The obtained single hole dispersion relation, line shapes of the spectral function and the remnant fermi surface could qualitatively explain those found in the recent photoemission experiments for insulating cuprate samples.