647 research outputs found
Bulk evidence for single-gap s-wave superconductivity in the intercalated graphite superconductor CYb
We report measurements of the in-plane electrical resistivity and the
thermal conductivity of the intercalated graphite superconductor
CYb to temperatures as low as /100. When a field is applied along the
c-axis, the residual electronic linear term evolves in an
exponential manner for . This activated behaviour
establishes the order parameter as unambiguously s-wave, and rules out the
possibility of multi-gap or unconventional superconductivity in this system.Comment: 4 pages, 4 figs, submitted to Phys. Rev. Let
Quantum oscillations in from an incommensurate -density wave order
We consider quantum oscillation experiments in
from the perspective of an incommensurate
Fermi surface reconstruction using an exact transfer matrix method and the
Pichard-Landauer formula for the conductivity. The specific density wave order
considered is a period-8 -density wave in which the current density is
unidirectionally modulated. The current modulation is also naturally
accompanied by a period-4 site charge modulation in the same direction, which
is consistent with recent magnetic resonance measurements. In principle Landau
theory also allows for a period-4 bond charge modulation, which is not
discussed, but should be simple to incorporate in the future. This scenario
leads to a natural, but not a unique, explanation of why only oscillations from
a single electron pocket is observed, and a hole pocket of roughly twice the
frequency as dictated by two-fold commensurate order, and the corresponding
Luttinger sum rule, is not observed. However, it is possible that even higher
magnetic fields will reveal a hole pocket of half the frequency of the electron
pocket or smaller. This may be at the borderline of achievable high field
measurements because at least a few complete oscillations have to be clearly
resolved.Comment: 8 pages, 7 figure
Onset of a boson mode at superconducting critical point of underdoped YBa2Cu3Oy
The thermal conductivity of underdoped \Y was measured in the limit as a function of hole concentration across the superconducting
critical point at = 5.0%. ``Time doping'' was used to resolve the
evolution of bosonic and fermionic contributions with high accuracy. For , we observe an additional contribution to
which we attribute to the boson excitations of a phase with long-range spin or
charge order. Fermionic transport, manifest as a linear term in , is
seen to persist unaltered through , showing that the state just below
is a thermal metal. In this state, the electrical resistivity varies
as log and the Wiedemann-Franz law is violated
Fermi-surface transformation across the pseudogap critical point of the cuprate superconductor LaNdSrCuO
The electrical resistivity and Hall coefficient R of the
tetragonal single-layer cuprate Nd-LSCO were measured in magnetic fields up to
T, large enough to access the normal state at , for closely
spaced dopings across the pseudogap critical point at .
Below , both coefficients exhibit an upturn at low temperature, which
gets more pronounced with decreasing . Taken together, these upturns show
that the normal-state carrier density at drops upon entering the
pseudogap phase. Quantitatively, it goes from at to at . By contrast, the mobility does not change appreciably, as
revealed by the magneto-resistance. The transition has a width in doping and
some internal structure, whereby R responds more slowly than to the
opening of the pseudogap. We attribute this difference to a Fermi surface that
supports both hole-like and electron-like carriers in the interval , with compensating contributions to R. Our data are in excellent
agreement with recent high-field data on YBCO and LSCO. The quantitative
consistency across three different cuprates shows that a drop in carrier
density from to is a universal signature of the pseudogap
transition at . We discuss the implication of these findings for the
nature of the pseudogap phase.Comment: 11 pages, 12 figure
Two types of nematicity in the phase diagram of the cuprate superconductor YBaCuO
Nematicity has emerged as a key feature of cuprate superconductors, but its
link to other fundamental properties such as superconductivity, charge order
and the pseudogap remains unclear. Here we use measurements of transport
anisotropy in YBaCuO to distinguish two types of nematicity. The
first is associated with short-range charge-density-wave modulations in a
doping region near . It is detected in the Nernst coefficient, but
not in the resistivity. The second type prevails at lower doping, where there
are spin modulations but no charge modulations. In this case, the onset of
in-plane anisotropy - detected in both the Nernst coefficient and the
resistivity - follows a line in the temperature-doping phase diagram that
tracks the pseudogap energy. We discuss two possible scenarios for the latter
nematicity.Comment: 8 pages and 7 figures. Main text and supplementary material now
combined into single articl
Nodes in the gap structure of the iron-arsenide superconductor Ba(Fe_{1-x}Co_x)_2As_2 from c-axis heat transport measurements
The thermal conductivity k of the iron-arsenide superconductor
Ba(Fe_{1-x}Co_x)_2As_2 was measured down to 50 mK for a heat current parallel
(k_c) and perpendicular (k_a) to the tetragonal c axis, for seven Co
concentrations from underdoped to overdoped regions of the phase diagram (0.038
< x < 0.127). A residual linear term k_c0/T is observed in the T = 0 limit when
the current is along the c axis, revealing the presence of nodes in the gap.
Because the nodes appear as x moves away from the concentration of maximal T_c,
they must be accidental, not imposed by symmetry, and are therefore compatible
with an s_{+/-} state, for example. The fact that the in-plane residual linear
term k_a0/T is negligible at all x implies that the nodes are located in
regions of the Fermi surface that contribute strongly to c-axis conduction and
very little to in-plane conduction. Application of a moderate magnetic field
(e.g. H_c2/4) excites quasiparticles that conduct heat along the a axis just as
well as the nodal quasiparticles conduct along the c axis. This shows that the
gap must be very small (but non-zero) in regions of the Fermi surface which
contribute significantly to in-plane conduction. These findings can be
understood in terms of a strong k dependence of the gap Delta(k) which produces
nodes on a Fermi surface sheet with pronounced c-axis dispersion and deep
minima on the remaining, quasi-two-dimensional sheets.Comment: 12 pages, 13 figures
The mitochondrial protease HtrA2 restricts the NLRP3 and AIM2 inflammasomes.
Activation of the inflammasome pathway is crucial for effective intracellular host defense. The mitochondrial network plays an important role in inflammasome regulation but the mechanisms linking mitochondrial homeostasis to attenuation of inflammasome activation are not fully understood. Here, we report that the Parkinson\u27s disease-associated mitochondrial serine protease HtrA2 restricts the activation of ASC-dependent NLRP3 and AIM2 inflammasomes, in a protease activity-dependent manner. Consistently, disruption of the protease activity of HtrA2 results in exacerbated NLRP3 and AIM2 inflammasome responses in macrophages ex vivo and systemically in vivo. Mechanistically, we show that the HtrA2 protease activity regulates autophagy and controls the magnitude and duration of inflammasome signaling by preventing prolonged accumulation of the inflammasome adaptor ASC. Our findings identify HtrA2 as a non-redundant mitochondrial quality control effector that keeps NLRP3 and AIM2 inflammasomes in check
Heavy holes: precursor to superconductivity in antiferromagnetic CeIn3
Numerous phenomenological parallels have been drawn between f- and d-
electron systems in an attempt to understand their display of unconventional
superconductivity. The microscopics of how electrons evolve from participation
in large moment antiferromagnetism to superconductivity in these systems,
however, remains a mystery. Knowing the origin of Cooper paired electrons in
momentum space is a crucial prerequisite for understanding the pairing
mechanism. Of especial interest are pressure-induced superconductors CeIn3 and
CeRhIn5 in which disparate magnetic and superconducting orders apparently
coexist - arising from within the same f-electron degrees of freedom. Here we
present ambient pressure quantum oscillation measurements on CeIn3 that
crucially identify the electronic structure - potentially similar to high
temperature superconductors. Heavy pockets of f-character are revealed in
CeIn3, undergoing an unexpected effective mass divergence well before the
antiferromagnetic critical field. We thus uncover the softening of a branch of
quasiparticle excitations located away from the traditional spin-fluctuation
dominated antiferromagnetic quantum critical point. The observed Fermi surface
of dispersive f-electrons in CeIn3 could potentially explain the emergence of
Cooper pairs from within a strong moment antiferromagnet.Comment: To appear in Proceedings of the National Academy of Science
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