1,790 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
Loschmidt-amplitude wave function spectroscopy and the physics of dynamically driven phase transitions
We introduce the Loschmidt amplitude as a powerful tool to perform spectroscopy of generic many-body wave functions and use it to interrogate the wave function obtained after ramping the transverse field quantum Ising model through its quantum critical point. Previous results are confirmed and a more complete understanding of the population of defects and of the effects of magnon-magnon interaction or finite-size corrections is obtained. The influence of quantum coherence is clarified
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
On the Critical Behavior of the Uniform Susceptibility of a Fermi Liquid Near an Antiferromagnetic Transition with Dynamic Exponent
We compute the leading behavior of the uniform magnetic susceptibility,
, of a Fermi liquid near an antiferromagnetic transition with dynamic
exponent . Our calculation clarifies the role of triangular ``anomaly''
graphs in the theory and justifies the effective action used in previous work
\cite{Hertz}. We find that at the critical point of a two dimensional
material, with and
nonuniversal constants. For reasonable band structures we find that in a
weak coupling approximation is small and positive. Our result suggests that
the behavior observed in the quantum critical regime of underdoped high-
superconductors are difficult to explain in a theory.Comment: 12 pages, uuencoded Postscript fil
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