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.

Reconstructing the bulk Fermi surface and the superconducting gap properties from Neutron Scattering experiments

We develop an analytical tool to extract bulk electronic properties of unconventional superconductors through inelastic neutron scattering (INS) spectra. Since the spin excitation spectrum in the superconducting (SC) state originates from Bogoliubov quasiparticle scattering associated with Fermi surface nesting, its energy-momentum relation--the so called `hour-glass' feature--can be inverted to reveal the Fermi momentum dispersion of the single-particle spectrum as well as the corresponding SC gap function. The inversion procedure is analogous to the quasiparticle interference (QPI) effect in scanning tunneling microscopy (STM). Whereas angle-resolved photoemission spectroscopy (ARPES) and STM provide surface sensitive information, our inversion procedure provides bulk electronic properties. The technique is essentially model independent and can be applied to a wide variety of materials.Comment: 8 pages, 4 figure

Evolution of Mid-gap States and Residual 3-Dimensionality in La2−x_{2-x}Srx_xCuO4_4

We have carried out extensive first principles doping-dependent computations of angle-resolved photoemission (ARPES) intensities in La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) over a wide range of binding energies. Intercell hopping and the associated 3-dimensionality, which is usually neglected in discussing cuprate physics, is shown to play a key role in shaping the ARPES spectra. Despite the obvious importance of strong coupling effects (e.g. the presence of a lower Hubbard band coexisting with mid-gap states in the doped insulator), we show that a number of salient features of the experimental ARPES spectra are captured to a surprisingly large extent when effects of $k_z$-dispersion are properly included in the analysis.Comment: 5 pages, 4 figure