2,196 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
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
Quasiparticle interference in iron-based superconductors
We systematically calculate quasiparticle interference (QPI) signatures for
the whole phase diagram of iron-based superconductors. Impurities inherent in
the sample together with ordered phases lead to distinct features in the QPI
images that are believed to be measured in spectroscopic imaging-scanning
tunneling microscopy (SI-STM). In the spin-density wave phase the rotational
symmetry of the electronic structure is broken, signatures of which are also
seen in the coexistence regime with both superconducting and magnetic order. In
the superconducting regime we show how the different scattering behavior for
magnetic and non-magnetic impurities allows to verify the symmetry of
the order parameter. The effect of possible gap minima or nodes is discussed.Comment: 19 pages, 7 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
Quasiparticle interference from different impurities on the surface of pyrochlore iridates: signatures of the Weyl phase
Weyl semimetals are gapless three-dimensional topological materials where two
bands touch at an even number of points in the bulk Brillouin zone. These
semimetals exhibit topologically protected surface Fermi arcs, which pairwise
connect the projected bulk band touchings in the surface Brillouin zone. Here,
we analyze the quasiparticle interference patterns of the Weyl phase when
time-reversal symmetry is explicitly broken. We use a multi-band -electron
Hubbard Hamiltonian on a pyrochlore lattice, relevant for the pyrochlore
iridate RIrO (where R is a rare earth). Using exact
diagonalization, we compute the surface spectrum and quasiparticle interference
(QPI) patterns for various surface terminations and impurities. We show that
the spin and orbital texture of the surface states can be inferred from the
absence of certain backscattering processes and from the symmetries of the QPI
features for non-magnetic and magnetic impurities. Furthermore, we show that
the QPI patterns of the Weyl phase in pyrochlore iridates may exhibit
additional interesting features that go beyond those found previously in TaAs.Comment: 15 pages, 16 figure
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
Content and guarantees of implementation the right to local self-government in the Russian Federation
This article covers the issue of the complex autonomous right, i.e. the right to local self-government and guaranty of its implementation. For the purposes of this paper the authors studied various theoretical approaches, legal and regulatory issues, practices of implementing the rights in the Russian Federation. It was founded that the right to local self-government is a complex and interconnected structure with several essential components (legal rights): right of a local community (population) for local self-governance, individual citizens’ rights, the members of this community, to participate in realizing self-governance and rights of the local authorities to exercise public power (local self-governance). In the result of this research the authors gave general definition and disclosed the content of the following terms: “citizen’s right to self-government”, and “citizen’s right to participate in realizing self-governance”. Constitutional right to self-government is just an integral part, a link in the system of rights and freedoms; due to this, we can consider this right as the unity with other rights. The guaranty of implementation of the right to self-government on the one hand gave better understanding of the problems of legislation concerning self-government and its improvement; on the other hand it helps to evaluate the conditions under which the citizens and municipal authorities carry out their activity. State and municipal guarantees are the part of the entire mechanism of implementation of the citizens’ right on self-government. They objectively exist and fulfil an important function protecting the rights of the population for self-government.peer-reviewe
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