1,260 research outputs found
Possible isotope effect on the resonance peak formation in high-T cuprates
Starting from the three-band Hubbard Hamiltonian we derive an effective
model including electron-phonon interaction of quasiparticles with
optical phonons. Within the effective Hamiltonian we analyze the influence of
electronic correlations and electron-phonon interaction on the dynamical spin
susceptibility in layered cuprates. We find a huge isotope effect on the
resonance peak in the magnetic spin susceptibility, ,
seen by inelastic neutron scattering. It results from both the electron-phonon
coupling and the electronic correlation effects taken into account beyond
random phase approximation(RPA) scheme. We find at optimal doping the isotope
coeffiecient which can be further tested
experimentally.Comment: revised version, new figure is added. Phys. Rev. B 69, 0945XX (2004);
in pres
Angular resolved specific heat in iron-based superconductors: the case for nodeless extended -wave gap
We consider the variation of the field-induced component of the specific heat
with the direction of the applied field in pnictides within
quasi-classical Doppler-shift approximation, with special emphasis to recent
experiments on FeSeTe [Zheng et al., arXiv:1004.2236]. We show
that for extended wave gap with no nodes, has
component, where is the angle between and the direction
between hole and electron Fermi surfaces. The maxima of are at
, , etc. if the applied field is smaller than , and
at , etc. if the applied field is larger than . The
angle-dependence of , the positions of the maxima, and the relative
magnitude of the oscillating component are consistent with the experiments
performed in the field of . We show that the observed
variation does not hold if the wave gap has accidental nodes along the two
electron Fermi surfaces.Comment: 5 pages, 4 figure
Unconventional superconductivity and magnetism in SrRuO and related materials
We review the normal and superconducting state properties of the
unconventional triplet superconductor SrRuO with an emphasis on the
analysis of the magnetic susceptibility and the role played by strong
electronic correlations. In particular, we show that the magnetic activity
arises from the itinerant electrons in the Ru -orbitals and a strong
magnetic anisotropy occurs () due to spin-orbit
coupling. The latter results mainly from different values of the -factor for
the transverse and longitudinal components of the spin susceptibility (i.e. the
matrix elements differ). Most importantly, this anisotropy and the presence of
incommensurate antiferromagnetic and ferromagnetic fluctuations have strong
consequences for the symmetry of the superconducting order parameter. In
particular, reviewing spin fluctuation-induced Cooper-pairing scenario in
application to SrRuO we show how p-wave Cooper-pairing with line nodes
between neighboring RuO-planes may occur.
We also discuss the open issues in SrRuO like the influence of
magnetic and non-magnetic impurities on the superconducting and normal state of
SrRuO. It is clear that the physics of triplet superconductivity in
SrRuO is still far from being understood completely and remains to be
analyzed more in more detail. It is of interest to apply the theory also to
superconductivity in heavy-fermion systems exhibiting spin fluctuations.Comment: short review article. Annalen der Physik, vol. 13 (2004), to be
publishe
Multiband Superconductivity in Spin Density Wave Metals
We study the emergence of multiband superconductivity with - and wave
symmetry on the background of spin density wave (SDW). We show that the SDW
coherence factors renormalize the momentum dependence of the superconducting
(SC) gap, yielding a SC state with an \emph{unconventional} s-wave symmetry.
Interband Cooper pair scattering stabilizes superconductivity in both
symmetries. With increasing SDW order, the s-wave state is more strongly
suppressed than the d-wave state. Our results are universally applicable to
two-dimensional systems with a commensurate SDW.Comment: 4 pages, 3 figure
Magnetic field dependence of the superconducting gap node topology in non-centrosymmetric CePtSi
The non-centrosymmetric superconductor CePtSi is believed to have a line
node in the energy gap arising from coexistence of s-wave and p-wave pairing.
We show that a weak c-axis magnetic field will remove this line node, since it
has no topological stability against time-reversal symmetry breaking
perturbations. Conversely a field in the plane is shown to remove the
line node on some regions of the Fermi surface, while bifurcating the line node
in other directions, resulting in two 'boomerang'-like shapes. These line node
topological changes are predicted to be observable experimentally in the low
temperature heat capacity.Comment: 4 pages, 3 figure
A fibre forming smectic twist-bent liquid crystalline phase
We demonstrate the nanostructure and filament formation of a novel liquid crystal phase of a dimeric mesogen below the twist–bend nematic phase. The new fibre-forming phase is distinguished by a short-correlated smectic order combined with an additional nanoscale periodicity that is not associated with density modulation
Dynamical charge susceptibility in layered cuprates: the influence of screened inter-site Coulomb repulsion
The analytical expression for dynamical charge susceptibility in layered
cuprates has been derived in the frame of singlet-correlated band model beyond
random-phase-approximation (RPA) scheme. Our calculations performed near
optimal doping regime show that there is a peak in real part of the charge
susceptibility at {\bf Q} = (, ) at strong
enough inter-site Coulomb repulsion. Together with the strong maximum in the Im
at 15 meV it confirms the formation of low-energetic
plasmons or charge fluctuations. This provides a jsutification that these
excitations are important and together with a spin flcutuations can contribute
to the Cooper pairing in layered cuprates. Analysing the charge susceptibilitiy
with respect to an instability we obtain a new plasmon branch, , along the Brillouin Zone. In particular, we have found that it goes to
zero near {\bf Q}
Polaron Effects on Superexchange Interaction: Isotope Shifts of , , and in Layered Copper Oxides
A compact expression has been obtained for the superexchange coupling of
magnetic ions via intermediate anions with regard to polaron effects at both
magnetic ions and intermediate anions. This expression is used to analyze the
main features of the behavior of isotope shifts for temperatures of three types
in layered cuprates: the Neel temperatures (), critical temperatures of
transitions to a superconducting state (), and characteristic temperatures
of the pseudogap in the normal state ().Comment: 4 pages, 1 figur
Spin susceptibility in bilayered cuprates: resonant magnetic excitations
We study the momentum and frequency dependence of the dynamical spin
susceptibility in the superconducting state of bilayer cuprate superconductors.
We show that there exists a resonance mode in the odd as well as the even
channel of the spin susceptibility, with the even mode being located at higher
energies than the odd mode. We demonstrate that this energy splitting between
the two modes arises not only from a difference in the interaction, but also
from a difference in the free-fermion susceptibilities of the even and odd
channels. Moreover, we show that the even resonance mode disperses downwards at
deviations from . In addition, we demonstrate that there
exists a second branch of the even resonance, similar to the recently observed
second branch (the -mode) of the odd resonance. Finally, we identify the
origin of the qualitatively different doping dependence of the even and odd
resonance. Our results suggest further experimental test that may finally
resolve the long-standing question regarding the origin of the resonance peak.Comment: 8 pages, 5 figure
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