1,435 research outputs found
Network patterns and strength of orbital currents in layered cuprates
In a frame of the model we derive the microscopical expression for
the circulating orbital currents in layered cuprates using the anomalous
correlation functions. In agreement with -on spin relaxation (SR),
nuclear quadrupolar resonance (NQR) and inelastic neutron scattering(INS)
experiments in YBaCuO we successfully explain the order of
magnitude and the monotonous increase of the {\it internal} magnetic fields
resulting from these currents upon cooling. However, the jump in the intensity
of the magnetic fields at T reported recently seems to indicate a
non-mean-field feature in the coexistence of current and superconducting states
and the deviation of the extended charge density wave vector instability from
its commensurate value {\bf Q}) in accordance with the
reported topology of the Fermi surface
Temperature Dependence of the Cu(2) NQR Line Width in YBaCuO
Systematic measurements of the Cu(2) NQR line width were performed in
underdoped YBaCuO samples over the temperature range 4.2 K
K. It was shown that the copper NQR line width monotonically increases
upon lowering temperature in the below-critical region, resembling temperature
behavior of the superconducting gap. The observed dependence is explained by
the fact that the energy of a condensate of sliding charge-current states of
the charge-density-wave type depends on the phase of order parameter.
Calculations show that this dependence appears only at . Quantitative
estimates of the line broadening at agree with the measurement results.Comment: 4 pages, 2 figure
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
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}
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
Superposition models and the multiplicity fluctuations in heavy ion collisions
A class of simple superposition models based on the Glauber picture of
multiple collisions is compared with the data on the centrality dependence of
the multiplicity distributions in a central rapidity bin. We show how the
results depend on the specific assumptions concerning the distributions in the
number of participants and their relations to the distributions of the number
of produced hadrons in various phase space bins. None of the versions of the
model describes satisfactorily the centrality dependence of the scaled
dispersion.Comment: 9 pages, 5 figures, a misprint in formula corrected, accepted for
publication in EPJ
Spin dynamics in the low-dimensional magnet TiOCl
We present detailed ESR investigations on single crystals of the
low-dimensional quantum magnet TiOCl. The anisotropy of the g-factor indicates
a stable orbital configuration below room temperature, and allows to estimate
the energy of the first excited state as 0.3(1) eV ruling out a possible
degeneracy of the orbital ground state. Moreover, we discuss the possible spin
relaxation mechanisms in TiOCl and analyze the angular and temperature
dependence of the linewidth up to 250 K in terms of anisotropic exchange
interactions. Towards higher temperatures an exponential increase of the
linewidth is observed, indicating an additional relaxation mechanism.Comment: 10 pages, 8 figures; accepted for publication in Phys. Rev.
Spin and Charge Josephson effects between non-uniform superconductors with coexisting helimagnetic order
We consider the spin and charge Josephson current between two non-uniform
Fulde-Ferrel-Larkin-Ovchinnikov superconductors with helimagnetic order. We
demonstrate that the presence of the helimagnetic phase generates a spin
Josephson effect and leads to additional contributions to both single-particle
and Josephson charge current. It is shown that for such systems the AC effect
differs more radically from the DC effect than in the case of a BCS
superconductor with helimagnetic order considered earlier in the literature [M.
L. Kuli\'c and I. M. Kuli\'c, Phys. Rev. B {\bf 63}, 104503 (2001)] where a
spin Josephson current has also been found. In our system the most interesting
effect occurs in the presence of an external magnetic field and in absence of
voltage, where we show that the charge Josephson current can be tuned to zero
while the spin Josephson current is non-vanishing. This provides a well
controlled mechanism to generate a spin supercurrent in absence of charge
currents.Comment: final versio
Superconductivity from repulsion in LiFeAs: novel s-wave symmetry and potential time-reversal symmetry breaking
We analyze the structure of the pairing interaction and superconducting gap
in LiFeAs by decomposing the pairing interaction for various kz cuts into s-
and d-wave components and by studying the leading superconducting
instabilities. We use the ten orbital tight-binding model, derived from
ab-initio LDA calculations with hopping parameters extracted from the fit to
ARPES experiments. We find that the pairing interaction almost decouples
between two subsets, one consists of the outer hole pocket and two electron
pockets, which are quasi-2D and are made largely out of dxy orbital, and the
other consists of the two inner hole pockets, which are quasi-3D and are made
mostly out of dxz and dyz orbitals. Furthermore, the bare inter-pocket and
intra-pocket interactions within each subset are nearly equal. In this
situation, small changes in the intra-pocket and inter-pocket interactions due
to renormalizations by high-energy fermions give rise to a variety of different
gap structures. We find four different configurations of the s-wave gap
immediately below Tc: the one in which superconducting gap changes sign between
two inner hole pockets and between the outer hole pocket and two electron
pockets, the one in which the gap changes sign between two electron pockets and
three hole pockets, the one in which the gap on the outer hole pocket differs
in sign from the gaps on the other four pockets, and the one in which the gaps
on two inner hole pockets have one sign, and the gaps on the outer hole pockets
and on electron pockets have different sign. Different s-wave gap
configurations emerge depending on whether the renormalized interactions
increase attraction within each subset or increase the coupling between
particular components of the two subsets. We argue that the state with opposite
sign of the gaps on the two inner hole pockets has the best overlap with ARPES
data.Comment: 23 pages, 15 figure
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