1,638 research outputs found
Phase diagram of geometric d-wave superconductor Josephson junctions
We show that a constriction-type Josephson junction realized by an epitactic
thin film of a d-wave superconductor with an appropriate boundary geometry
exhibits intrinsic phase differences between 0 and pi depending on geometric
parameters and temperature. Based on microscopic Eilenberger theory, we provide
a general derivation of the relation between the change of the free energy of
the junction and the current-phase relation. From the change of the free
energy, we calculate phase diagrams and discuss transitions driven by geometric
parameters and temperature.Comment: 9 pages, 11 figures. Phys. Rev. B, accepte
Josephson effect in ballistic graphene
We solve the Dirac-Bogoliubov-De-Gennes equation in an impurity-free
superconductor-normal-superconductor (SNS) junction, to determine the maximal
supercurrent that can flow through an undoped strip of graphene with heavily
doped superconducting electrodes. The result is determined by the
superconducting gap and by the aspect ratio of the junction (length L, small
relative to the width W and to the superconducting coherence length). Moving
away from the Dirac point of zero doping, we recover the usual ballistic result
in which the Fermi wave length takes over from L. The product of critical
current and normal-state resistance retains its universal value (up to a
numerical prefactor) on approaching the Dirac point.Comment: 4 pages, 2 figure
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Dual separable feedback systems govern firing rate homeostasis.
Firing rate homeostasis (FRH) stabilizes neural activity. A pervasive and intuitive theory argues that a single variable, calcium, is detected and stabilized through regulatory feedback. A prediction is that ion channel gene mutations with equivalent effects on neuronal excitability should invoke the same homeostatic response. In agreement, we demonstrate robust FRH following either elimination of Kv4/Shal protein or elimination of the Kv4/Shal conductance. However, the underlying homeostatic signaling mechanisms are distinct. Eliminating Shal protein invokes KrĂĽppel-dependent rebalancing of ion channel gene expression including enhanced slo, Shab, and Shaker. By contrast, expression of these genes remains unchanged in animals harboring a CRISPR-engineered, Shal pore-blocking mutation where compensation is achieved by enhanced IKDR. These different homeostatic processes have distinct effects on homeostatic synaptic plasticity and animal behavior. We propose that FRH includes mechanisms of proteostatic feedback that act in parallel with activity-driven feedback, with implications for the pathophysiology of human channelopathies
Impurity band in clean superconducting weak links
Weak impurity scattering produces a narrow band with a finite density of
states near the phase difference in the mid-gap energy spectrum of
a macroscopic superconducting weak link. The equivalent distribution of
transmission coefficients of various cunducting quantum channels is found.Comment: 4 pages, 4 figures, changed conten
Spectrum of Andreev Bound States in a Molecule Embedded Inside a Microwave-Excited Superconducting Junction
Non-dissipative Josephson current through nanoscale superconducting
constrictions is carried by spectroscopically sharp energy states, so-called
Andreev bound states. Although theoretically predicted almost 40 years ago, no
direct spectroscopic evidence of these Andreev bound states exists to date. We
propose a novel type of spectroscopy based on embedding a superconducting
constriction, formed by a single-level molecule junction, in a microwave QED
cavity environment. In the electron-dressed cavity spectrum we find a polariton
excitation at twice the Andreev bound state energy, and a superconducting-phase
dependent ac Stark shift of the cavity frequency. Dispersive measurement of
this frequency shift can be used for Andreev bound state spectroscopy.Comment: Published version; 4+ pages, 3 figure
Non-collinear single-electron spin-valve transistors
We study interaction effects on transport through a small metallic cluster
connected to two ferromagnetic leads (a single-electron spin-valve transistor)
in the "orthodox model" for the Coulomb blockade. The non-local exchange
between the spin accumulation on the island and the ferromagnetic leads is
shown to affect the transport properties such as the electric current and
spin-transfer torque as a function of the magnetic configuration, gate voltage,
and applied magnetic field.Comment: 4 pages, 3 figure
Excitation gap of a graphene channel with superconducting boundaries
We calculate the density of states of electron-hole excitations in a
superconductor/normal-metal/superconductor (SNS) junction in graphene, in the
long-junction regime that the superconducting gap is much larger than the
Thouless energy. If the normal region is undoped, the excitation spectrum
consists of neutral modes that propagate along the boundaries - transporting
energy but no charge. These ``Andreev modes'' are a coherent superposition of
electron states from the conduction band and hole states from the valence band,
coupled by specular Andreev reflection at the superconductor. The lowest
Andreev mode has an excitation gap, which depends on the superconducting phase
difference across the SNS graphene channel. At high doping the excitation gap
vanishes and the usual gapless density of states of Andreev levels is
recovered. We use our results to calculate the superconducting phase dependence
of the thermal conductance of the graphene channel.Comment: 8 pages, 10 figure
Morphological Characteristic to Discriminate \u3cem\u3eFestulolium\u3c/em\u3e Hybrids (\u3cem\u3eFestuca Pratensis\u3c/em\u3e Ă— \u3cem\u3eLolium Perenne\u3c/em\u3e)
Environmental change and uncertainty is likely to pose new challenges in plant breeders. Recently attention has focused on the crossing of Lolium and Festuca species to obtain hybrids exhibiting many desirable traits of both parents. Key objectives of such programs are to combine the persistency, winter hardiness and drought tolerance of fescues with the high herbage yields and quality of ryegrasses (Zwierzykowski, Naganowska, 1994). One of the hybrids with great practical significance is a F. pratensis Ă— L. perenne hybrid [Festulolium loliaceum (Huds.) P.V. Fourn]. Many morphological traits of Festulolium hybrids demonstrate intermediate character, however, in relation to inflorescence type they are similar to L. perenne; the hybrids and perennial ryegrass have spike-like inflorescences, though they may be rarely a little-branched. Occurrence of a reduced inner glume in hybrid spikelets is a trait, which enables discrimination between Festulolium and L. perenne plants. The aim of this work was to analyse the morphological trait of inflorescences to aid the identification of the hybrids Festulolium in relation to L. perenne
Rate equations for Coulomb blockade with ferromagnetic leads
We present a density-matrix rate-equation approach to sequential tunneling
through a metal particle weakly coupled to ferromagnetic leads. The
density-matrix description is able to deal with correlations between degenerate
many-electron states that the standard rate equation formalism in terms of
occupation probabilities cannot describe. Our formalism is valid for an
arbitrary number of electrons on the dot, for an arbitrary angle between the
polarization directions of the leads, and with or without spin-orbit scattering
on the metal particle. Interestingly, we find that the density-matrix
description may be necessary even for metal particles with unpolarized leads if
three or more single-electron levels contribute to the transport current and
electron-electron interactions in the metal particle are described by the
`universal interaction Hamiltonian'.Comment: 10 pages, 4 figures, REVTeX
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