Quarks, Gluons and Frustrated Antiferromagnets

The Contractor Renormalization Group method (CORE) is used to establish the equivalence of various Hamiltonian free fermion theories and a class of generalized frustrated antiferromagnets. In particular, after a detailed discussion of a simple example, it is argued that a generalized frustrated SU(3) antiferromagnet whose single-site states have the quantum numbers of mesons and baryons is equivalent to a theory of free massless quarks. Furthermore, it is argued that for slight modification of the couplings which define the frustrated antiferromagnet Hamiltonian, the theory becomes a theory of quarks interacting with color gauge-fields.Comment: 21 pages, Late

Nonuniversality in quantum wires with off-diagonal disorder: a geometric point of view

It is shown that, in the scaling regime, transport properties of quantum wires with off-diagonal disorder are described by a family of scaling equations that depend on two parameters: the mean free path and an additional continuous parameter. The existing scaling equation for quantum wires with off-diagonal disorder [Brouwer et al., Phys. Rev. Lett. 81, 862 (1998)] is a special point in this family. Both parameters depend on the details of the microscopic model. Since there are two parameters involved, instead of only one, localization in a wire with off-diagonal disorder is not universal. We take a geometric point of view and show that this nonuniversality follows from the fact that the group of transfer matrices is not semi-simple. Our results are illustrated with numerical simulations for a tight-binding model with random hopping amplitudes.Comment: 12 pages, RevTeX; 3 figures included with eps

Influence of higher d-wave gap harmonics on the dynamical magnetic susceptibility of high-temperature superconductors

Using a fermiology approach to the computation of the magnetic susceptibility measured by neutron scattering in hole-doped high-Tc superconductors, we estimate the effects on the incommensurate peaks caused by higher d-wave harmonics of the superconducting order parameter induced by underdoping. The input parameters for the Fermi surface and d-wave gap are taken directly from angle resolved photoemission (ARPES) experiments on Bi{2}Sr{2}CaCu{2}O{8+x} (Bi2212). We find that higher d-wave harmonics lower the momentum dependent spin gap at the incommensurate peaks as measured by the lowest spectral edge of the imaginary part in the frequency dependence of the magnetic susceptibility of Bi2212. This effect is robust whenever the fermiology approach captures the physics of high-Tc superconductors. At energies above the resonance we observe diagonal incommensurate peaks. We show that the crossover from parallel incommensuration below the resonance energy to diagonal incommensuration above it is connected to the values and the degeneracies of the minima of the 2-particle energy continuum.Comment: 13 pages, 7 figure