935 research outputs found
Dispersion and damping of zone-boundary magnons in the noncentrosymmetric superconductor CePt3Si
Inelastic neutron scattering (INS) is employed to study damped spin-wave
excitations in the noncentrosymmetric heavy-fermion superconductor CePt3Si
along the antiferromagnetic Brillouin-zone boundary in the low-temperature
magnetically ordered state. Measurements along the (1/2 1/2 L) and (H H 1/2-H)
reciprocal-space directions reveal deviations in the spin-wave dispersion from
the previously reported model. Broad asymmetric shape of the peaks in energy
signifies strong spin-wave damping by interactions with the particle-hole
continuum. Their energy width exhibits no evident anomalies as a function of
momentum along the (1/2 1/2 L) direction, which could be attributed to
Fermi-surface nesting effects, implying the absence of pronounced commensurate
nesting vectors at the magnetic zone boundary. In agreement with a previous
study, we find no signatures of the superconducting transition in the magnetic
excitation spectrum, such as a magnetic resonant mode or a superconducting spin
gap, either at the magnetic ordering wavevector (0 0 1/2) or at the zone
boundary. However, the low superconducting transition temperature in this
material still leaves the possibility of such features being weak and therefore
hidden below the incoherent background at energies ~0.1 meV, precluding their
detection by INS
The Anomalous Infrared Emission of Abell 58
We present a new model to explain the excess in mid and near infrared
emission of the central, hydrogen poor dust knot in the planetary nebula (PN)
Abell 58. Current models disagree with ISO measurement because they apply an
average grain size and equilibrium conditions only. We investigate grain size
distributions and temperature fluctuations affecting infrared emission using a
new radiative transfer code and discuss in detail the conditions requiring an
extension of the classical description. The peculiar infrared emission of V605
Aql, the central dust knot in Abell 58, has been modeled with our code. V605
Aql is of special interest as it is one of only three stars ever observed to
move from the evolutionary track of a central PN star back to the post-AGB
state.Comment: 17 pages, 4 figures; accepted and to be published in Ap
Possible pseudogap behavior of electron doped high-temperature superconductors
We have measured the low-energy quasiparticle excitation spectrum of the
electron doped high-temperature superconductors (HTS) Nd(1.85)Ce(0.15)CuO(4-y)
and Pr(1.85)Ce(0.15)CuO(4-y) as a function of temperature and applied magnetic
field using tunneling spectroscopy. At zero magnetic field, for these optimum
doped samples no excitation gap is observed in the tunneling spectra above the
transition temperature Tc. In contrast, below Tc for applied magnetic fields
well above the resistively determined upper critical field, a clear excitation
gap at the Fermi level is found which is comparable to the superconducting
energy gap below Tc. Possible interpretations of this observation are the
existence of a normal state pseudogap in the electron doped HTS or the
existence of a spatially non-uniform superconducting state.Comment: 4 pages, 4 ps-figures included, to be published in Phys. Rev. B,
Rapid Com
Theory for phonon-induced superconductivity in MgB
We analyze superonductivity in MgB observed below K resulting
from electron-phonon coupling involving a mode at meV and
most importantly the in-plane B-B vibration at
meV. The quasiparticles originating from - and -states couple
strongly to the low-frequency mode and the -vibrations respectively.
Using two-band Eliashberg theory, and , we calculate the gap functions (,
).
Our results provide an explanation of recent tunneling experiments.
We get .Comment: revised version, accepted for publication in PR
Doping dependence of the many-body effects along the nodal direction in the high-Tc cuprate (Bi,Pb)_2Sr_2CaCu_2O_8
Angle-resolved photoemission spectroscopy (ARPES) is used to study the doping
dependence of the lifetime and the mass renormalization of the low energy
excitations in the high-Tc cuprate (Bi,Pb)_2Sr_2CaCu_2O_8 along the zone
diagonal. We find a linear energy de-pendence of the scattering rate for the
underdoped samples and a quadratic energy depend-ence in the overdoped case.
The mass enhancement of the quasiparticles due to the many body effects at the
Fermi energy is found to be in the order of 2 and the renormalization extends
over a large energy range for both the normal and the superconducting state.
The much discussed kink in the dispersion around 70 meV is interpreted as a
small additional effect at low temperatures.Comment: 12 pages, 3 figure
Drug-resistant genotypes and multi-clonality in Plasmodium falciparum analysed by direct genome sequencing from peripheral blood of malaria patients.
Naturally acquired blood-stage infections of the malaria parasite Plasmodium falciparum typically harbour multiple haploid clones. The apparent number of clones observed in any single infection depends on the diversity of the polymorphic markers used for the analysis, and the relative abundance of rare clones, which frequently fail to be detected among PCR products derived from numerically dominant clones. However, minority clones are of clinical interest as they may harbour genes conferring drug resistance, leading to enhanced survival after treatment and the possibility of subsequent therapeutic failure. We deployed new generation sequencing to derive genome data for five non-propagated parasite isolates taken directly from 4 different patients treated for clinical malaria in a UK hospital. Analysis of depth of coverage and length of sequence intervals between paired reads identified both previously described and novel gene deletions and amplifications. Full-length sequence data was extracted for 6 loci considered to be under selection by antimalarial drugs, and both known and previously unknown amino acid substitutions were identified. Full mitochondrial genomes were extracted from the sequencing data for each isolate, and these are compared against a panel of polymorphic sites derived from published or unpublished but publicly available data. Finally, genome-wide analysis of clone multiplicity was performed, and the number of infecting parasite clones estimated for each isolate. Each patient harboured at least 3 clones of P. falciparum by this analysis, consistent with results obtained with conventional PCR analysis of polymorphic merozoite antigen loci. We conclude that genome sequencing of peripheral blood P. falciparum taken directly from malaria patients provides high quality data useful for drug resistance studies, genomic structural analyses and population genetics, and also robustly represents clonal multiplicity
Pseudogap from ARPES experiment: three gaps in cuprates and topological superconductivity
A term first coined by Mott back in 1968 a `pseudogap' is the depletion of
the electronic density of states at the Fermi level, and pseudogaps have been
observed in many systems. However, since the discovery of the high temperature
superconductors (HTSC) in 1986, the central role attributed to the pseudogap in
these systems has meant that by many researchers now associate the term
pseudogap exclusively with the HTSC phenomenon. Recently, the problem has got a
lot of new attention with the rediscovery of two distinct energy scales
(`two-gap scenario') and charge density waves patterns in the cuprates. Despite
many excellent reviews on the pseudogap phenomenon in HTSC, published from its
very discovery up to now, the mechanism of the pseudogap and its relation to
superconductivity are still open questions. The present review represents a
contribution dealing with the pseudogap, focusing on results from angle
resolved photoemission spectroscopy (ARPES) and ends up with the conclusion
that the pseudogap in cuprates is a complex phenomenon which includes at least
three different `intertwined' orders: spin and charge density waves and
preformed pairs, which appears in different parts of the phase diagram. The
density waves in cuprates are competing to superconductivity for the electronic
states but, on the other hand, should drive the electronic structure to
vicinity of Lifshitz transition, that could be a key similarity between the
superconducting cuprates and iron based superconductors. One may also note that
since the pseudogap in cuprates has multiple origins there is no need to recoin
the term suggested by Mott.Comment: invited review, more info at http://www.imp.kiev.ua/~kor
Interplay of ferromagnetism and triplet superconductivity in a Josephson junction
In this paper we extend our earlier analysis of the novel Josephson effect in
triplet superconductor--ferromagnet--triplet superconductor (TFT) junctions [B.
Kastening \emph{et al.}, Phys. Rev. Lett. {\bf{96}}, 047009 (2006)]. In our
more general formulation of the TFT junction we allow for potential scattering
at the barrier and an arbitrary orientation of the ferromagnetic moment.
Several new effects are found upon the inclusion of these extra terms: for
example, we find that a Josephson current can flow even when there is vanishing
phase difference between the superconducting condensates on either side of the
barrier. The critical current for a barrier with magnetization parallel to the
interface is calculated as a function of the junction parameters, and is found
to display strong non-analyticities. Furthermore, the Josephson current
switches first identified in our previous work are found to be robust features
of the junction, while the unconventional temperature-dependence of the current
is very sensitive to the extra terms in the barrier Hamiltonian.Comment: 24 pages, 15 figure
Non-Fermi liquid behavior and scaling of low frequency suppression in optical conductivity spectra of CaRuO
Optical conductivity spectra of paramagnetic CaRuO are
investigated at various temperatures. At T=10 K, it shows a non-Fermi liquid
behavior of , similar to the case
of a ferromagnet SrRuO. As the temperature () is increased, on the other
hand, in the low frequency region is progressively
suppressed, deviating from the 1/{\omega}^{\frac 12%}-dependence.
Interestingly, the suppression of is found to scale with
at all temperatures. The origin of the scaling
behavior coupled with the non-Fermi liquid behavior is discussed.Comment: 4 pages, 3 figure
Nonmonotonic d_{x^2-y^2} Superconducting Order Parameter in Nd_{2-x}Ce_xCuO_4
Low energy polarized electronic Raman scattering of the electron doped
superconductor Nd_1.85Ce_0.15CuO_4 (T_c=22 K) has revealed a nonmonotonic
d_{x^2-y^2} superconducting order parameter. It has a maximum gap of 4.4 k_BT_c
at Fermi surface intersections with antiferromagnetic Brillouin zone (the ``hot
spots'') and a smaller gap of 3.3 k_BT_c at fermionic Brillouin zone
boundaries. The gap enhancement in the vicinity of the ``hot spots'' emphasizes
role of antiferromagnetic fluctuations and similarity in the origin of
superconductivity for electron- and hole-doped cuprates.Comment: 4 pages, 4 figure
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