1,439 research outputs found
On the "spin-freezing" mechanism in underdoped superconducting cuprates
The letter deals with the spin-freezing process observed by means of NMR-NQR
relaxation or by muon spin rotation in underdoped cuprate superconductors. This
phenomenon, sometimes referred as coexistence of antiferromagnetic and
superconducting order parameters, is generally thought to result from randomly
distributed magnetic moments related to charge inhomogeneities (possibly
stripes) which exhibit slowing down of their fluctuations on cooling below
T . Instead, we describe the experimental findings as due to fluctuating,
vortex-antivortex, orbital currents state coexisting with d-wave
superconducting state. A direct explanation of the experimental results, in
underdoped YCaBaCuO and LaSrCuO,
is thus given in terms of freezing of orbital current fluctuations
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
Multi-Cascade Proton Acceleration by Superintense Laser Pulse in the Regime of Relativistically Induced Slab Transparency
A regime of multi-cascade proton acceleration in the interaction of
W/cm laser pulse with a structured target is proposed.
The regime is based on the electron charge displacement under the action of
laser ponderomotive force and on the effect of relativistically induced slab
transparency which allows to realize idea of multi-cascade acceleration. It is
shown that a target comprising several properly spaced apart thin foils can
optimize the acceleration process and give at the output quasi-monoenergetic
beams of protons with energies up to hundreds of MeV with energy spread of just
few percent.Comment: 5 pages with 4 figure
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
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
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
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