2,520 research outputs found
Comment on "A Tale of Two Theories: Quantum Griffiths Effects in Metallic Systems" by A. H. Castro-Neto and B. A. Jones
In a recent paper Castro-Neto and Jones argue that because the observability
of quantum Griffiths-McCoy effects in metals is controlled by non-universal
quantities, the quantum Griffiths-McCoy scenario may be a viable explanation
for the non-fermi-liquid behavior observed in heavy fermion compounds. In this
Comment we point out that the important non-universal quantity is the damping
of the spin dynamics by the metallic electrons; quantum Griffiths-McCoy effects
occur only if this is parametrically weak relative to other scales in the
problem, i.e. if the spins are decoupled from the carriers. This suggests that
in heavy fermion materials, where the Kondo effect leads to a strong
carrier-spin coupling, quantum Griffiths-McCoy effects are unlikely to occur.Comment: 2 page
Role of oxygen-oxygen hopping in the three-band copper-oxide model: quasiparticle weight, metal insulator and magnetic phase boundaries, gap values and optical conductivity
We investigate the effect of oxygen-oxygen hopping on the three-band
copper-oxide model relevant to high- cuprates, finding that the physics is
changed only slightly as the oxygen-oxygen hopping is varied. The location of
the metal-insulator phase boundary in the plane of interaction strength and
charge transfer energy shifts by eV or less along the charge transfer
axis, the quasiparticle weight has approximately the same magnitude and doping
dependence and the qualitative characteristics of the electron-doped and
hole-doped sides of the phase diagram do not change. The results confirm the
identification of LaCuO as a material with intermediate correlation
strength. However, the magnetic phase boundary as well as higher-energy
features of the optical spectrum are found to depend on the magnitude of the
oxygen-oxygen hopping. We compare our results to previously published one-band
and three-band model calculations.Comment: 13.5 pages, 16 figure
On the Josephson Coupling between a disk of one superconductor and a surrounding superconducting film of a different symmetry
A cylindrical Josephson junction with a spatially dependent Josephson
coupling which averages to zero is studied in order to model the physics of a
disk of d-wave superconductor embedded in a superconducting film of a different
symmetry. It is found that the system always introduces Josepshon vortices in
order to gain energy at the junction. The critical current is calculated. It is
argued that a recent experiment claimed to provide evidence for s-wave
superconductivity in may also be consistent with d-wave
superconductivity. Figures available from the author on request.Comment: 10 pages, revtex3.0, TM-11111-940321-1
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