2,776 research outputs found
Probing the superconducting ground state of the rare-earth ternary boride superconductors RuB ( = Lu,Y) using muon-spin rotation and relaxation
The superconductivity in the rare-earth transition metal ternary borides
RuB (where = Lu and Y) has been investigated using muon-spin
rotation and relaxation. Measurements made in zero-field suggest that
time-reversal symmetry is preserved upon entering the superconducting state in
both materials; a small difference in depolarization is observed above and
below the superconducting transition in both compounds, however this has been
attributed to quasistatic magnetic fluctuations. Transverse-field measurements
of the flux-line lattice indicate that the superconductivity in both materials
is fully gapped, with a conventional s-wave pairing symmetry and BCS-like
magnitudes for the zero-temperature gap energies. The electronic properties of
the charge carriers in the superconducting state have been calculated, with
effective masses and in the Lu
and Y compounds, respectively, with superconducting carrier densities
() m and ()
m. The materials have been classified according to the
Uemura scheme for superconductivity, with values for
of and , implying that
the superconductivity may not be entirely conventional in nature.Comment: 8 pages, 8 figure
Time-reversal symmetry breaking in noncentrosymmetric superconductor Re6Hf:further evidence for unconventional behaviour in the alpha-Mn family of materials
The discovery of new families of unconventional superconductors is important
both experimentally and theoretically, especially if it challenges current
models and thinking. By using muon spin relaxation in zero-field, time-reversal
symmetry breaking has been observed in Re6Hf. Moreover, the temperature
dependence of the superfluid density exhibits s-wave superconductivity with an
enhanced electron-phonon coupling. This, coupled with the results from
isostructural Re6Zr, shows that the Re6X family are indeed a new and important
group of unconventional superconductors.Comment: 5 pages, 2 figures Accepted Physical Review B, Rapid Communicatio
Continued surprises in the cytochrome c biogenesis story.
Cytochromes c covalently bind their heme prosthetic groups through thioether bonds between the vinyl groups of the heme and the thiols of a CXXCH motif within the protein. In Gram-negative bacteria, this process is catalyzed by the Ccm (cytochrome c maturation) proteins, also called System I. The Ccm proteins are found in the bacterial inner membrane, but some (CcmE, CcmG, CcmH, and CcmI) also have soluble functional domains on the periplasmic face of the membrane. Elucidation of the mechanisms involved in the transport and relay of heme and the apocytochrome from the bacterial cytosol into the periplasm, and their subsequent reaction, has proved challenging due to the fact that most of the proteins involved are membrane-associated, but recent progress in understanding some key components has thrown up some surprises. In this Review, we discuss advances in our understanding of this process arising from a substrate's point of view and from recent structural information about individual components
Superconducting and normal-state properties of the noncentrosymmetric superconductor Re6Zr
We systematically investigate the normal and superconducting properties of
non-centrosymmetric ReZr using magnetization, heat capacity, and
electrical resistivity measurements. Resistivity measurements indicate
ReZr has poor metallic behavior and is dominated by disorder. ReZr
undergoes a superconducting transition at K. Magnetization measurements give a lower critical
field, mT. The
Werthamer-Helfand-Hohenberg model is used to approximate the upper critical
field T which is close to
the Pauli limiting field of 12.35 T and which could indicate singlet-triplet
mixing. However, low-temperature specific-heat data suggest that ReZr is
an isotropic, fully gapped s-wave superconductor with enhanced electron-phonon
coupling. Unusual flux pinning resulting in a peak effect is observed in the
magnetization data, indicating an unconventional vortex state.Comment: 11 pages, 7 figures, 2 table
Probing the superconducting ground state of the noncentrosymmetric superconductors CaTSi3 (T = Ir, Pt) using muon-spin relaxation and rotation
The superconducting properties of CaTSi3 (where T = Pt and Ir) have been
investigated using muon spectroscopy. Our muon-spin relaxation results suggest
that in both these superconductors time-reversal symmetry is preserved, while
muon-spin rotation data show that the temperature dependence of the superfluid
density is consistent with an isotropic s-wave gap. The magnetic penetration
depths and upper critical fields determined from our transverse-field muon-spin
rotation spectra are found to be 448(6) and 170(6) nm, and 3800(500) and
1700(300) G, for CaPtSi3 and CaIrSi3 respectively. The superconducting
coherence lengths of the two materials have also been determined and are 29(2)
nm for CaPtSi3 and 44(4) nm for CaIrSi3.Comment: 6 pages, 7 figure
Combining experiment and energy landscapes to explore anaerobic heme breakdown in multifunctional hemoproteins
To survive, many pathogens extract heme from their host organism and break down the porphyrin scaffold to sequester the Fe2+ ion via a heme oxygenase. Recent studies have revealed that certain pathogens can anaerobically degrade heme. Our own research has shown that one such pathway proceeds via NADH-dependent heme degradation, which has been identified in a family of hemoproteins from a range of bacteria. HemS, from Yersinia enterocolitica, is the main focus of this work, along with HmuS (Yersinia pestis), ChuS (Escherichia coli) and ShuS (Shigella dysenteriae). We combine experiments, Energy Landscape Theory, and a bioinformatic investigation to place these homologues within a wider phylogenetic context. A subset of these hemoproteins are known to bind certain DNA promoter regions, suggesting not only that they can catalytically degrade heme, but that they are also involved in transcriptional modulation responding to heme flux. Many of the bacterial species responsible for these hemoproteins (including those that produce HemS, ChuS and ShuS) are known to specifically target oxygen-depleted regions of the gastrointestinal tract. A deeper understanding of anaerobic heme breakdown processes exploited by these pathogens could therefore prove useful in the development of future strategies for disease prevention
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