1,013 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
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
Magnetic degeneracy and hidden metallicity of the spin density wave state in ferropnictides
We analyze spin density wave (SDW) order in iron-based superconductors and
electronic structure in the SDW phase. We consider an itinerant model for
Fe-pnictides with two hole bands centered at and two electron bands
centered at and in the unfolded BZ. A SDW order in such a
model is generally a combination of two components with momenta and
, both yield order in the folded zone. Neutron
experiments, however, indicate that only one component is present. We show that
or order is selected if we assume that only one hole band
is involved in the SDW mixing with electron bands. A SDW order in such 3-band
model is highly degenerate for a perfect nesting and hole-electron interaction
only, but we show that ellipticity of electron pockets and interactions between
electron bands break the degeneracy and favor the desired or
order. We further show that stripe-ordered system remains a metal for
arbitrary coupling. We analyze electronic structure for parameters relevant to
the pnictides and argue that the resulting electronic structure is in good
agreement with ARPES experiments. We discuss the differences between our model
and model of localized spins.Comment: reference list updated, typos are correcte
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