2,335 research outputs found
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
Suppression of superconductivity by Neel-type magnetic fluctuations in the iron pnictides
Motivated by recent experimental detection of Neel-type ()
magnetic fluctuations in some iron pnictides, we study the impact of competing
and spin fluctuations on the superconductivity of these
materials. We show that, counter-intuitively, even short-range, weak Neel
fluctuations strongly suppress the state, with the main effect arising
from a repulsive contribution to the pairing interaction, complemented
by low frequency inelastic scattering. Further increasing the strength of the
Neel fluctuations leads to a low- d-wave state, with a possible
intermediate phase. The results suggest that the absence of
superconductivity in a series of hole-doped pnictides is due to the combination
of short-range Neel fluctuations and pair-breaking impurity scattering, and
also that of optimally doped pnictides could be further increased if
residual fluctuations were reduced.Comment: revised version accepted for publication in PR
Lifshitz Transition in Underdoped Cuprates
Recent studies show that quantum oscillations thought to be associated with a
density wave reconstructed Fermi surface disappear at a critical value of the
doping for YBa2Cu3O6+y, and the cyclotron mass diverges as the critical value
is approached from the high doping side. We argue that the phenomenon is due to
a Lifshitz transition where the pockets giving rise to the quantum oscillations
connect to form an open (quasi-1d) Fermi surface. The estimated critical doping
is close to that found by experiment, and the theory predicts a logarithmic
divergence of the cyclotron mass with a coefficient comparable to that observed
in experiment.Comment: 4 pages, 4 figure
Antiphase Stripe Order as the Origin of Electron Pockets Observed in 1/8-Hole-Doped Cuprates
Recent quantum oscillation measurements on underdoped cuprates are shown to
be consistent with the predictions of a mean field theory of the 1/8 magnetic
antiphase stripe order proposed to occur in high- cuprates. In particular,
for intermediate values of the stripe order parameter, the magneto-transport is
found to be dominated by an electron pocket
The antiferromagnetic phase of the Floquet-driven Hubbard model
A saddle point plus fluctuations analysis of the periodically driven
half-filled two-dimensional Hubbard model is performed. For drive frequencies
below the equilibrium gap, we find discontinuous transitions to time-dependent
solutions. A highly excited, generically non-thermal distribution of magnons
occurs even for drive frequencies far above the gap. Above a critical drive
amplitude, the low-energy magnon distribution diverges as the frequency tends
to zero and antiferromagnetism is destroyed, revealing the generic importance
of collective mode excitations arising from a non-equilibrium drive
Test Experiment for Time-Reversal Symmetry Breaking Superconductivity
A new experiment is proposed to probe the time-reversal symmetry of a
superconductor. It is shown that a time-reversal symmetry breaking
superconductor can be identified by the observation of a fractional flux in
connection with a Josephson junction in a special geometry.Comment: 4 pages, 2 figures available upon request, Revtex, MIT-CMT-OC
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