Carmine Lubritto

The role of apical oxygen in the high-temperature superconductors

We report finite-cluster diagonalizations which clarify the role of apical oxygen orbitals and of the copper orbitals in the ground-state electronic properties of high-temperature superconductors. The hole density distribution and spin - spin correlation functions are analysed as functions of interoxygen hopping and other parameters. The main conclusion is that for universally accepted parameters for planes, small levels of doping and no phonons, the three-band Hamiltonian suffices to describe the properties of the ground state and the inverse photoemission.

A microscopic bosonization procedure of the chiral edge field theory for Laughlin states

Abstract A unified microscopic bosonization of the edge chiral field theory both for the Integer Quantum Hall Effect and the Laughlin wavefunction is given, without relying on the corresponding classical plasma. The edge excitations for the Laughlin wavefunction are adiabatically constructed starting from those of the integer case.

Adiabatic heuristic construction of trial wave functions for quantum Hall states at arbitrary fractional fillings

Abstract Starting from a lowest Landau level filled with several electron species, adiabatic interpolation through anyon hamiltonians is considered. The antisymmetrized final states are explicitriial wave functions for identical electrons, depending on three integer parameters, and generalize the Laughlin wave function to arbitrary fractional fillings. Space Carlo simulations. Numerical results are consistent with energies reported by other authors using much less simple trial wave functions.

Chiral boson field theory for neutral and charged edge excitations of Laughlin liquids in smooth confining potentials

Abstract A microscopic construction of the chiral boson edge field theory for neutral and charged excitations of generalized Laughlins states in smooth confining potentials for two-edge geometries is described. This is done by taking account of the topological degrees of freedom of the two chiral fields, which obey a joint constraint due to overall neutrality. This establishes a thorough correspondence with some traits of the heterotic string construction.

Exact solution of the Anderson lattice model with infinite-range hopping

Abstract We present the exact solution of the Anderson lattice model, under the assumption of constant hopping amplitudes between any pair of lattice sites. Special care is devoted to the behaviour of the double occupation density for correlated electrons and to the occurrence of a metal-insulator transition driven by variations of the electron density.

Approximate holomorphic representation for lowest Landau level wave functions in a cylindrically symmetrical electric field

The single particle aspects of an approximation scheme for electrons in the presence of a cylindrically symmetrical electric field whose symmetry axis has the same direction as that of a uniform magnetic field are considered. The approximation, previously proposed in the realm of the fractional quantum Hall effect, is tested numerically for a particular electric field interpolating between a bulk vanishing value and an edge harmonic field, and proved to be reliable if two conditions are obeyed.

Trial wave functions for quantum Hall edge states

Abstract Trial wave functions for Laughlins liquids in the presence of confining potentials are considered. They lead to a description of fractional quantum Hall edge states as a prototype of the chiral Luttinger liquid. Their reliability is confirmed by Monte Carlo simulation of the equivalent classical plasma.

A generalized FQHE trial wave function on spherical geometry

Abstract Using Haldanes spherical model, new microscopic trial wave functions originally built on disk geometry are mapped onto the sphere. These wave functions were obtained for arbitrary fractional filling by adiabatic interpolation through anyon Hamiltonians. Monte Carlo methods have been employed to evaluate the ground state energy at different fillings using up to 128 electrons on a sphere. Results are consistent with extrapolation of exact system diagonalization and earlier Monte Carlo calculations.

A new FQHE trial wave function for planar and spherical geometry

We propose new trial wave functions generalizing the Laughlin wave function for the Fractional Quantum Hall Effect of arbitrary fractional filling. Starting from a system ofN interacting electrons with a “colour” quantum number, we obtain, by an adiabatic interpolation through anyon hamiltonians, a trial wave function for identical electrons both for planar and spherical geometry. Monte Carlo simulations of the equivalent classical plasma give ground state energies confirming the reliability of the proposed wave functions.

A molecular model for strongly correlated electron systems

Abstract We present exact results for a diatomic molecule described by the Ansderson model which includes both on-site and intersite hybridization, as well as the on-site Coulomb repulsion between f - and conduction electrons (the Falicov-Kimball term). The mixed valence behaviour is demonstrated in the subspace with N = 2 electrons, while the competition between Kondo screening and RKKY interaction is investigated for N = 4 electrons. The Falicov-Kimball term restricts the range of stability of the mixed valence state, and increases the values of the Kondo temperature and of the crossover temperature to disordered f -moments in the Kondo and RKKY regime, respectively, while it increases the temperature above which the ferromagnetic correlations between f -moments are destabilized for N = 3 electrons.