2,463 research outputs found
Are there nodes in LaFePO, BaFe(AsP), and KFeAs ?
We reexamined the experimental evidences for the possible existence of the
superconducting (SC) gap nodes in the three most suspected Fe-pnictide SC
compounds: LaFePO, BaFe(AsP), and KFeAs. We
showed that while the -linear temperature dependence of the penetration
depth of these three compounds indicate extremely clean nodal gap
superconductors, the thermal conductivity data unambiguously showed that LaFePO and
BaFe(AsP) are extremely dirty, while KFeAs
can be clean. This apparently conflicting experimental data casts a serious
doubt on the nodal gap possibility on LaFePO and
BaFe(AsP).Comment: 11 pages, 5 figures A new section "4. Remark on the quantum
oscillation (QO) experiments" is adde
Wiedemann-Franz law and non-vanishing temperature scale across the field-tuned quantum critical point of YbRh2Si2
The in-plane thermal conductivity kappa(T) and electrical resistivity rho(T)
of the heavy-fermion metal YbRh2Si2 were measured down to 50 mK for magnetic
fields H parallel and perpendicular to the tetragonal c axis, through the
field-tuned quantum critical point, Hc, at which antiferromagnetic order ends.
The thermal and electrical resistivities, w(T) and rho(T), show a linear
temperature dependence below 1 K, typical of the non-Fermi liquid behavior
found near antiferromagnetic quantum critical points, but this dependence does
not persist down to T = 0. Below a characteristic temperature T* ~ 0.35 K,
which depends weakly on H, w(T) and rho(T) both deviate downward and converge
in the T = 0 limit. We propose that T* marks the onset of short-range magnetic
correlations, persisting beyond Hc. By comparing samples of different purity,
we conclude that the Wiedemann-Franz law holds in YbRh2Si2, even at Hc,
implying that no fundamental breakdown of quasiparticle behavior occurs in this
material. The overall phenomenology of heat and charge transport in YbRh2Si2 is
similar to that observed in the heavy-fermion metal CeCoIn5, near its own
field-tuned quantum critical point.Comment: 8 figures, 8 page
Atomic-scale coexistence of short-range magnetic order and superconductivity in FeSeTe
The ground state of the parent compounds of many high temperature
superconductors is an antiferromagnetically (AFM) ordered phase, where
superconductivity emerges when the AFM phase transition is suppressed by doping
or application of pressure. This behaviour implies a close relation between the
two orders. Understanding the interplay between them promises a better
understanding of how the superconducting condensate forms from the AFM ordered
background. Here we explore this relation in real space at the atomic scale
using low temperature spin-polarized scanning tunneling microscopy (SP-STM) and
spectroscopy. We investigate the transition from antiferromagnetically ordered
via the spin glass phase in
to superconducting
. In
we observe an
atomic-scale coexistence of superconductivity and short-ranged bicollinear
antiferromagnetic order.Comment: 7 pages, 6 figure
From d-wave to s-wave pairing in the iron-pnictide superconductor (Ba,K)Fe2As2
The nature of the pairing state in iron-based superconductors is the subject
of much debate. Here we argue that in one material, the stoichiometric iron
pnictide KFe2As2, there is overwhelming evidence for a d-wave pairing state,
characterized by symmetry-imposed vertical line nodes in the superconducting
gap. This evidence is reviewed, with a focus on thermal conductivity and the
strong impact of impurity scattering on the critical temperature Tc. We then
compare KFe2As2 to Ba0.6K0.4Fe2As2, obtained by Ba substitution, where the
pairing symmetry is s-wave and the Tc is ten times higher. The transition from
d-wave to s-wave within the same crystal structure provides a rare opportunity
to investigate the connection between band structure and pairing mechanism. We
also compare KFe2As2 to the nodal iron-based superconductor LaFePO, for which
the pairing symmetry is probably not d-wave, but more likely s-wave with
accidental line nodes
Doping dependence of heat transport in the iron-arsenide superconductor Ba(FeCo)As: from isotropic to strongly -dependent gap structure
The temperature and magnetic field dependence of the in-plane thermal
conductivity of the iron-arsenide superconductor
Ba(FeCo)As was measured down to mK and up to
T as a function of Co concentration in the range 0.048 0.114. In zero magnetic field, a negligible residual linear term in
as at all shows that there are no zero-energy
quasiparticles and hence the superconducting gap has no nodes in the -plane
anywhere in the phase diagram. However, the field dependence of
reveals a systematic evolution of the superconducting gap with doping , from
large everywhere on the Fermi surface in the underdoped regime, as evidenced by
a flat at , to strongly -dependent in the overdoped
regime, where a small magnetic field can induce a large residual linear term,
indicative of a deep minimum in the gap magnitude somewhere on the Fermi
surface. This shows that the superconducting gap structure has a strongly
-dependent amplitude around the Fermi surface only outside the
antiferromagnetic/orthorhombic phase.Comment: version accepted for publication in Physical Review Letters; new
title, minor revision, revised fig.1, and updated reference
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