6,023 research outputs found
Volovik effect in the s-wave state for the iron-based superconductors
We studied the field dependencies of specific heat coefficient and thermal conductivity coefficient of the s-wave state in the mixed state. We
found that it is a generic feature of the two band s-wave state with the
unequal sizes of gaps, small and large , that Doppler
shift of the quasiparticle excitations (Volovik effect) creates a finite
density of states, on the extended states outside of vortex cores, proportional
to in contrast to the dependence of the d-wave state. Impurity
scattering effect on the s-wave state, however, makes this generic
-linear dependence sublinear approaching to the behavior. Our
calculations of successfully fit the
experimental data of Ba(FeCo As with different Co-doping
by systematically varying the gap size ratio . We also resolve the dilemma of a substantial value of but almost zero value of , observed in experiments.Comment: 5 pages, 2 figures accepted to Phys. Rev. Lett
Volovik effect on NMR measurements of unconventional superconuctors
We studied the Volovik effect on the NMR measurements of the two
unconventional superconducting (SC) states, the d-wave and s-wave states.
We showed the generic field dependencies of the spin-lattice relaxation rate
and Knight shift at low temperature limit in the pure cases as:
, for the d-wave, and , for the s-wave state, respectively. Performing
numerical calculations we showed that these generic power laws survive for the
good part of low field region with the realistic amount of impurities. We also
found that the Volovik effect acts as an equivalent pair breaker as the unitary
impurity scattering, hence induces the same temperature evolutions on
and , respectively, as the unitary impurities in both SC states. This
finding implies that the Volovik effect should always be taken into account for
the analysis of the NMR measurements in the mixed state.Comment: 5 pages, 4 figures; The fitting function of the inset of Fig.2(a) is
slightly change
Effective potential for composite operators and for an auxiliary scalar field in a Nambu-Jona-Lasinio model
We derive the effective potentials for composite operators in a
Nambu-Jona-Lasinio (NJL) model at zero and finite temperature and show that in
each case they are equivalent to the corresponding effective potentials based
on an auxiliary scalar field. The both effective potentials could lead to the
same possible spontaneous breaking and restoration of symmetries including
chiral symmetry if the momentum cutoff in the loop integrals is large enough,
and can be transformed to each other when the Schwinger-Dyson (SD) equation of
the dynamical fermion mass from the fermion-antifermion vacuum (or thermal)
condensates is used. The results also generally indicate that two effective
potentials with the same single order parameter but rather different
mathematical expressions can still be considered physically equivalent if the
SD equation corresponding to the extreme value conditions of the two potentials
have the same form.Comment: 7 pages, no figur
Unstable states in quantum many-body theory
Unstable states of a general type of many-body system characterized by a combination of outgoing waves and bound states in all channels are investigated. It is seen, that the time-development in general will contain both oscillating and exponentially decaying terms
Nuclear spin-lattice relaxation rate in the D+iD superconducting state: implications for CoO superconductor
We calculated the nuclear spin-lattice relaxation rate for the D+iD
superconducting state with impurities. We found that small amount of unitary
impurities quickly produces the residual density of states inside the gap. As a
result, the T-linear behavior in 1/T is observed at low temperatures. Our
results show that the D+iD pairing symmetry of the superconducting state of
NaCoOH O is compatible with recent Co 1/T
experiments of several groups.Comment: 5 pages, 4 figures, minor change
Collapse arrest and soliton stabilization in nonlocal nonlinear media
We investigate the properties of localized waves in systems governed by
nonlocal nonlinear Schrodinger type equations. We prove rigorously by bounding
the Hamiltonian that nonlocality of the nonlinearity prevents collapse in,
e.g., Bose-Einstein condensates and optical Kerr media in all physical
dimensions. The nonlocal nonlinear response must be symmetric, but can be of
completely arbitrary shape. We use variational techniques to find the soliton
solutions and illustrate the stabilizing effect of nonlocality.Comment: 4 pages with 3 figure
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