Contrasting Pathways to Mott Gap Collapse in Electron and Hole Doped Cuprates

Recent ARPES measurements on the electron-doped cuprate Nd_{2-x}Ce_xCuO_4 can be interpreted in a mean field model of uniform doping of an antiferromagnet, with the Mott gap closing near optimal doping. Mode coupling calculations confirm the mean field results, while clarifying the relation between the Mott gap and short-range magnetic order. The same calculations find that hole doped cuprates should follow a strikingly different doping dependence, involving instability toward spiral phases or stripes. Nevertheless, the magnetic order (now associated with stripes) again collapses near optimal doping.Comment: 5 eps figures, revtex. Presented at the ``Workshop on Intrinsic Multiscale Structure and Dynamics in Complex Electronic Oxides'', at the International Center for Theoretical Physics, Trieste, Italy, July 1-4, 2002; to be published, in ``Intrinsic Multiscale Structure and Dynamics in Complex Electronic Oxides'', edited by A.R. Bishop, S.R. Shenoy, and S. Sridhar, World Scientific (2003

Chaos in a Jahn-Teller Molecule

The Jahn-Teller system E x b_1 + b_2 has a particular degeneracy, where the vibronic potential has an elliptical minimum. In the general case where the ellipse does not reduce to a circle, the classical motion in the potential is chaotic, tending to trapping near one of the extrema of the ellipse. In the quantum problem, the motion consists of correlated tunneling from one extremum to the opposite, leading to an average angular momentum reminiscent of that of the better known E x e dynamic Jahn-Teller system.Comment: 7 eps figures, revtex. To be published, Phys. Rev.

Stripe Disordering Transition

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.Comment: 4 pages LaTex, 2 ps figures (U. of Miami Conference HTS99