8,059 research outputs found
Incoherent pair tunneling in the pseudogap phase of cuprates
Motivated by a recent experiment by Bergeal et al., we reconsider incoherent
pair tunneling in a cuprate junction formed from an optimally doped
superconducting lead and an underdoped normal metallic lead. We study the
impact of the pseudogap on the pair tunneling by describing fermions in the
underdoped lead with a model self-energy that has been developed to reproduce
photoemission data. We find that the pseudogap causes an additional temperature
dependent suppression of the pair contribution to the tunneling current. We
discuss consistency with available experimental data and propose future
experimental directions.Comment: 5 pages, 3 figure
Phase soliton and pairing symmetry of a two-band superconductor: Role of the proximity effect
We suggest a mechanism which promotes the existence of a phase soliton --
topological defect formed in the relative phase of superconducting gaps of a
two-band superconductor with s+- type of pairing. This mechanism exploits the
proximity effect with a conventional s-wave superconductor which favors the
alignment of the phases of the two-band superconductor which, in the case of
s+- pairing, are pi-shifted in the absence of proximity. In the case of a
strong proximity such effect can be used to reduce soliton's energy below the
energy of a soliton-free state thus making the soliton thermodynamically
stable. Based on this observation we consider an experimental setup, applicable
both for stable and metastable solitons, which can be used to distinguish
between s+- and s++ types of pairing in the iron-based multiband
superconductors.Comment: New references, added discussion about self-consistency of the GL
description of a phase soliton in the presence of a proximity patc
Transport implications of Fermi arcs in the pseudogap phase of the cuprates
We derive the fermionic contribution to the longitudinal and Hall
conductivities within a Kubo formalism, using a phenomenological Greens
function which has been previously developed to describe photoemission data in
the pseudogap phase of the cuprates. We find that the in-plane electrical and
thermal conductivities are metallic-like, showing a universal limit behavior
characteristic of a d-wave spectrum as the scattering rate goes to zero. In
contrast, the c-axis resistivity and the Hall number are insulating-like, being
divergent in the same limit. The relation of these results to transport data in
the pseudogap phase is discussed.Comment: 3 pages, 2 figure
A structured approach for the engineering of biochemical network models, illustrated for signalling pathways
http://dx.doi.org/10.1093/bib/bbn026Quantitative models of biochemical networks (signal transduction cascades, metabolic pathways, gene regulatory circuits) are a central component of modern systems biology. Building and managing these complex models is a major challenge that can benefit from the application of formal methods adopted from theoretical computing science. Here we provide a general introduction to the field of formal modelling, which emphasizes the intuitive biochemical basis of the modelling process, but is also accessible for an audience with a background in computing science and/or model engineering. We show how signal transduction cascades can be modelled in a modular fashion, using both a qualitative approach { Qualitative Petri nets, and quantitative approaches { Continuous Petri Nets and Ordinary Differential Equations. We review the major elementary building blocks of a cellular signalling model, discuss which critical design decisions have to be made during model building, and present ..
Novel Quaternary Dilute Magnetic Semiconductor (Ga,Mn)(Bi,As): Magnetic and Magneto-Transport Investigations
Magnetic and magneto-transport properties of thin layers of the
(Ga,Mn)(Bi,As) quaternary dilute magnetic semiconductor grown by the
low-temperature molecular-beam epitaxy technique on GaAs substrates have been
investigated. Ferromagnetic Curie temperature and magneto-crystalline
anisotropy of the layers have been examined by using magneto-optical Kerr
effect magnetometry and low-temperature magneto-transport measurements.
Postgrowth annealing treatment has been shown to enhance the hole concentration
and Curie temperature in the layers. Significant increase in the magnitude of
magnetotransport effects caused by incorporation of a small amount of Bi into
the (Ga,Mn)As layers revealed in the planar Hall effect (PHE) measurements, is
interpreted as a result of enhanced spin-orbit coupling in the (Ga,Mn)(Bi,As)
layers. Two-state behaviour of the planar Hall resistance at zero magnetic
field provides its usefulness for applications in nonvolatile memory devices.Comment: 10 pages, 3 figures, to be published in the Proceedings of ICSM-2016
conferenc
Dissipation of Quantum Turbulence in the Zero Temperature Limit
Turbulence, produced by an impulsive spin-down from angular velocity Omega to
rest of a cube-shaped container, is investigated in superfluid 4He at
temperatures 0.08 K - 1.6 K. The density of quantized vortex lines L is
measured by scattering negative ions. Homogeneous turbulence develops after
time t of approximately 20 \Omega and decays as L proportional to t^(-3/2). The
corresponding energy flux epsilon = nu' (kappa L)^2, which is proportional to
t^(-3), is characteristic of quasi-classical turbulence at high Re with a
saturated energy-containing length. The effective kinematic viscosity in the
T=0 limit is nu' = 0.003 kappa, where kappa=10^(-3) cm^2 / s is the circulation
quantum.Comment: 4 pages, 5 figures. Updated following referees comment
Ab initio data-analytics study of carbon-dioxide activation on semiconductor oxide surfaces
The excessive emissions of carbon dioxide (CO2) into the atmosphere threaten to shift the CO2 cycle planet-wide and induce unpredictable climate changes. Using artificial intelligence (AI) trained on high-throughput first principles based data for a broad family of oxides, we develop a strategy for a rational design of catalytic materials for converting CO2 to fuels and other useful chemicals. We demonstrate that an electron transfer to the π-antibonding orbital of the adsorbed molecule and the associated bending of the initially linear molecule, previously proposed as the indicator of activation, are insufficient to account for the good catalytic performance of experimentally characterized oxide surfaces. Instead, our AI model identifies the common feature of these surfaces in the binding of a molecular O atom to a surface cation, which results in a strong elongation and therefore weakening of one molecular C-O bond. This finding suggests using the C-O bond elongation as an indicator of CO2 activation. Based on these findings, we propose a set of new promising oxide-based catalysts for CO2 conversion, and a recipe to find more
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