109 research outputs found
Global critical temperature in disordered superconductors with weak multifractality
There is growing evidence, from experiments and numerical simulations, that a
key feature of sufficiently disordered superconductors is the spatial
inhomogeneity of the order parameter. However not much is known analytically
about the details of its spatial distribution or the associated global critical
temperature that signals the breaking of long-range order. Here we address this
problem for disordered systems around an Anderson transition characterized by
multifractal one-body eigenstates. In the limit of weak multifractality and for
weakly coupled superconductors we compute the superconducting order parameter
analytically, including its energy dependence and statistical distribution in
space. The spatial distribution of the order parameter is found to be always
log-normal. The global critical temperature, computed by percolation techniques
and neglecting phase fluctuations, is enhanced with respect to the clean limit
only for very weakly coupled superconductors. Some enhancement still persists
even in the presence of moderate phase fluctuations crudely modelled by
increasing the percolation threshold. Our results are also consistent with
experiments, where enhancement of the critical temperature is observed in Al
thin films, a very weakly coupled metallic superconductor, but not in more
strongly coupled materials.A.M.G. was supported by EPSRC, Grant No. EP/I004637/1, FCT, Grant PTDC/FIS/111348/2009, and a Marie Curie International Reintegration Grant PIRG07-GA-2010-268172. J.M. acknowledges the support of an EPSRC Ph.D. studentship.This is the author accepted manuscript. The final version is available from APS via http://dx.doi.org/10.1103/PhysRevB.92.17452
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
Delineation of the frequency and boundary of chromosomal copy number variations in paediatric neuroblastoma
© 2018 Informa UK Limited, trading as Taylor & Francis Group. Neuroblastoma, the most common solid tumour in early childhood, is characterized by very frequent chromosomal copy number variations (CNVs). While chromosome 2p amplification, 17q gain, 1p and 11q deletion in human neuroblastoma tissues are well-known, the exact frequencies and boundaries of the chromosomal CNVs have not been delineated. We analysed the publicly available single nucleotide polymorphism (SNP) array data which were originally generated by the Therapeutically Applicable Research to Generate Effective Treatments (TARGET) initiative, defined the frequencies and boundaries of chromosomes 2p11.2–2p25.3 amplification, 17q11.1-17q25.3 gain, 1p13.3-1p36.33 deletion and 11q13.3-11q25 deletion in neuroblastoma tissues, and identified chromosome 7q14.1 (Chr7:38254795-38346971) and chromosome 14q11.2 (Chr14:21637401-22024617) deletion in blood and bone marrow samples from neuroblastoma patients, but not in tumour tissues. Kaplan Meier analysis showed that double deletion of Chr7q14.1 and Chr14q11.2 correlated with poor prognosis in MYCN gene amplified neuroblastoma patients. In conclusion, the oncogenes amplified or gained and tumour suppressor genes deleted within the boundaries of chromosomal CNVs in tumour tissues should be studied for their roles in tumourigenesis and as therapeutic targets. Focal deletions of Chr7q14.1 and Chr14q11.2 together in blood and bone marrow samples from neuroblastoma patients can be used as a marker for poorer prognosis and more aggressive therapies
Superconductivity and the upper critical field in the chiral noncentrosymmetric superconductor NbRh2B2
NbRh2B2 crystallises in a chiral noncentrosymmetric structure and exhibits bulk type-II superconductivity below 7.46(5) K. Here we show that the temperature dependence of the upper critical field deviates from the behaviour expected for both Werthamer-Helfand-Hohenberg and the Ginzburg-Landau models and that μ0Hc2 (0) ~ 18 T exceeds the Pauli paramagnetic limit, μ0HP = 13.9 T. We explore the reasons for this enhancement. Transverse-field muon spectroscopy measurements suggest that the superconducting gap is either s-wave or (s + s)-wave, a the pressure dependence of Tc reveals the superconducting gap is primarily s- wave in character. The magnetic penetration depth lambda(0) = 595(5) nm. Heat capacity measurements reveal the presence of a multigap (s + s)-wave superconducting order parameter and moderate electron-phonon coupling
Shape-resonant superconductivity in nanofilms: from weak to strong coupling
Ultrathin superconductors of different materials are becoming a powerful
platform to find mechanisms for enhancement of superconductivity, exploiting
shape resonances in different superconducting properties. Here we evaluate the
superconducting gap and its spatial profile, the multiple gap components, and
the chemical potential, of generic superconducting nanofilms, considering the
pairing attraction and its energy scale as tunable parameters, from weak to
strong coupling, at fixed electron density. Superconducting properties are
evaluated at mean field level as a function of the thickness of the nanofilm,
in order to characterize the shape resonances in the superconducting gap. We
find that the most pronounced shape resonances are generated for weakly coupled
superconductors, while approaching the strong coupling regime the shape
resonances are rounded by a mixing of the subbands due to the large energy gaps
extending over large energy scales. Finally, we find that the spatial profile,
transverse to the nanofilm, of the superconducting gap acquires a flat behavior
in the shape resonance region, indicating that a robust and uniform multigap
superconducting state can arise at resonance.Comment: 7 pages, 4 figures. Submitted to the Proceedings of the Superstripes
2016 conferenc
Dynamics of Nonequilibrium Dicke Models
Motivated by experiments observing self-organization of cold atoms in optical
cavities we investigate the collective dynamics of the associated
nonequilibrium Dicke model. The model displays a rich semiclassical phase
diagram of long time attractors including distinct superradiant fixed points,
bistable and multistable coexistence phases and regimes of persistent
oscillations. We explore the intrinsic timescales for reaching these asymptotic
states and discuss the implications for finite duration experiments. On the
basis of a semiclassical analysis of the effective Dicke model we find that
sweep measurements over 200ms may be required in order to access the asymptotic
regime. We briefly comment on the corrections that may arise due to quantum
fluctuations and states outside of the effective two-level Dicke model
description.Comment: 27 pages, 20 figure
Anisotropic superconductivity and unusually robust electronic critical field in single crystal La7Ir3
Polycrystalline LaIr is reported to show superconductivity
breaking time-reversal symmetry while also having an isotropic -wave gap.
Single crystals of this noncentrosymmetric superconductor are highly desirable
to understand the nature of the electron pairing mechanism in this system. Here
we report the growth of high-quality single crystals of LaIr by the
Czochralski method. The structural and superconducting properties of these
large crystals have been investigated using x-rays, magnetization, resistivity
and heat capacity measurements. We observe a clear anisotropy in the lower and
upper critical fields for magnetic fields applied parallel and perpendicular to
the hexagonal axis. We also report the presence of a robust electronic
critical field, that diverges from the upper critical field derived from heat
capacity, which is the hallmark of surface superconductivity.Comment: 20 + 5 pages, 6 + 4 figures, 1 + 1 tables. Accepted for publication
into Physical Review Material
Glutamine addiction promotes glucose oxidation in triple-negative breast cancer
Glutamine is a conditionally essential nutrient for many cancer cells, but it remains unclear how consuming glutamine in excess of growth requirements confers greater fitness to glutamine-addicted cancers. By contrasting two breast cancer subtypes with distinct glutamine dependencies, we show that glutamine-indispensable triple-negative breast cancer (TNBC) cells rely on a non-canonical glutamine-to-glutamate overflow, with glutamine carbon routed once through the TCA cycle. Importantly, this single-pass glutaminolysis increases TCA cycle fluxes and replenishes TCA cycle intermediates in TNBC cells, a process that achieves net oxidation of glucose but not glutamine. The coupling of glucose and glutamine catabolism appears hard-wired via a distinct TNBC gene expression profile biased to strip and then sequester glutamine nitrogen, but hampers the ability of TNBC cells to oxidise glucose when glutamine is limiting. Our results provide a new understanding of how metabolically rigid TNBC cells are sensitive to glutamine deprivation and a way to select vulnerable TNBC subtypes that may be responsive to metabolic-targeted therapies
Giant topological and planar Hall effect in Cr1/3NbS2
Cr1/3NbS2 is a transition metal dichalcogenide that has been of significant interest due to its ability to host a magnetic chiral soliton lattice. Conventional and planar Hall measurements provide valuable insight into the detection of exotic spin structures in chiral magnets. We show that the presence of a giant planar Hall effect (PHE) can be attributed to a tilted soliton lattice in Cr1/3NbS2. Our detailed angular-dependent study shows the PHE and anisotropic magnetoresistance are intrinsically linked in complex noncoplanar magnets. From the conventional Hall signal we show the presence of a giant unconventional, likely topological Hall component that is the fingerprint of noncoplanar spin textures
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