181 research outputs found
Enhanced Pairing in the "Checkerboard" Hubbard Ladder
We study signatures of superconductivity in a 2--leg "checkerboard" Hubbard
ladder model, defined as a one--dimensional (period 2) array of square
plaquettes with an intra-plaquette hopping and inter-plaquette hopping
, using the density matrix renormalization group method. The highest
pairing scale (characterized by the spin gap or the pair binding energy,
extrapolated to the thermodynamic limit) is found for doping levels close to
half filling, and . Other forms of modulated
hopping parameters, with periods of either 1 or 3 lattice constants, are also
found to enhance pairing relative to the uniform two--leg ladder, although to a
lesser degree. A calculation of the phase stiffness of the ladder reveals that
in the regime with the strongest pairing, the energy scale associated with
phase ordering is comparable to the pairing scale.Comment: 9 pages, 9 figures; Journal reference adde
Quasiparticle scattering and local density of states in graphite
We determine the effect of quasiparticle interference on the spatial
variations of the local density of states (LDOS) in graphite in the
neighborhood of an isolated impurity. A number of characteristic behaviors of
interference are identified in the Fourier transformed spectrum. A comparison
between our results and scanning tunneling microscopy (STM) experiments could
provide a critical test of the range (of energy) of applicability of the Fermi
liquid description of graphite, where some evidence of the breakdown of Fermi
liquid theory has recently been discussed. Moreover, given the similarity
between the band structures of graphite and that of nodal quasiparticles in a
d-wave superconductor, a comparison between results in the two materials is
useful for understanding the physics of the cuprates.Comment: 5 pages, 4 figures, RevTex
Observable NMR signal from circulating current order in YBCO
Assuming, as suggested by recent neutron scattering experiments, that a
broken symmetry state with orbital current order occurs in the pseudo-gap phase
of the cuprate superconductors, we show that there must be associated
equilibrium magnetic fields at various atomic sites in the unit cell, which
should be detectable by NMR experiments
An exact chiral spin liquid with non-Abelian anyons
We establish the existence of a chiral spin liquid (CSL) as the exact ground
state of the Kitaev model on a decorated honeycomb lattice, which is obtained
by replacing each site in the familiar honeycomb lattice with a triangle. The
CSL state spontaneously breaks time reversal symmetry but preserves other
symmetries. There are two topologically distinct CSLs separated by a quantum
critical point. Interestingly, vortex excitations in the topologically
nontrivial (Chern number ) CSL obey non-Abelian statistics.Comment: 4 pages, 2 figures; published version in Phys. Rev. Let
High Temperature Superconductivity: Ineluctable Complexity
The discovery of charge-density-wave order in the high-temperature
superconductor YBaCuO places charge order centre stage with
superconductivity, suggesting they they are intertwined rather than competing.Comment: 3 pages, 1 figure, 19 references; News & Views article for Nature
Physic
Fragile Mott Insulators
We prove that there exists a class of crystalline insulators, which we call
"fragile Mott insulators" which are not adiabatically connected to any sort of
band insulator provided time-reversal and certain point-group symmetries are
respected, but which are otherwise unspectacular in that they exhibit no
topological order nor any form of fractionalized quasiparticles. Different
fragile Mott insulators are characterized by different nontrivial
one-dimensional representations of the crystal point group. We illustrate this
new type of insulators with two examples: the d-Mott insulator discovered in
the checkerboard Hubbard model at half-filling and the
Affleck-Kennedy-Lieb-Tasaki insulator on the square lattice.Comment: 4 pages, 2 figures. Published version in PRL. The name "Weak Mott
Insulators" is changed to "Fragile Mott Insulators" to avoid confusing in
terminolog
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