80 research outputs found
Bis({tris[2-(3,5-di-tert-butyl-2-oxidobenzylideneamino)ethyl]amine}cerium(III)) diethyl ether solvate
The title compound, 2[Ce(C51H75N4O3)]·C4H10O, was obtained in high yield (92%) by reduction of (TRENDSAL)CeIVCl [TRENDSAL is N,N′,N′′-tris(3,5-di-tert-butylsalicylidenatoamino)triethylamine] with potassium in THF. The bulky tripodal TRENDSAL ligand effectively encapsulates the central CeIII cation with a Ce—N(imine) distance of 2.860 (2) Å and an average C—N(amine) distance of 2.619 Å within a distorted monocapped octahedral coordination
Depinning of a vortex chain in a disordered flow channel
We study depinning of vortex chains in channels formed by static, disordered
vortex arrays. Depinning is governed either by the barrier for defect
nucleation or for defect motion, depending on whether the chain periodicity is
commensurate or incommensurate with the surrounding arrays. We analyze the
reduction of the gap between these barriers as function of disorder. At large
disorder, commensurability becomes irrelevant and the pinning force is reduced
to a small fraction of the ideal shear strength of ordered channels.
Implications for experiments on channel devices are discussed.Comment: 5 pages, 4 figures. Accepted for publication in Europhysics Letter
Tris(N,N′-diisopropylbenzamidinato)cerium(III)
The title compound, [Ce(C13H19N2)3], was obtained in moderate yield (67%) by treatment of anhydrous cerium trichloride with three equivalents of Li[PhC(NiPr)2] in tetrahydrofuran. It is the first homoleptic lanthanide complex of this amidinate ligand. The central CeIII ion is coordinated by three chelating benzamidinate anions in a distorted octahedral fashion, with Ce—N distances in the narrow range 2.482 (2)–2.492 (2) Å. The dihedral angles between the phenyl rings and the chelating N—C—N units are in the range 73.3–87.9°, thus preventing conjugation between the two π-systems. The molecule is located on a twofold rotation axis, and one of the phenyl rings is equally disordered over two alternative symmetry-equivalent positions around this axis
Metastability in Josephson transmission lines
Thermal activation and macroscopic quantum tunneling in current-biased
discrete Josephson transmission lines are studied theoretically. The degrees of
freedom under consideration are the phases across the junctions which are
coupled to each other via the inductances of the system. The resistively
shunted junctions that we investigate constitute a system of N interacting
degrees of freedom with an overdamped dynamics. We calculate the decay rate
within exponential accuracy as a function of temperature and current. Slightly
below the critical current, the decay from the metastable state occurs via a
unique ("rigid") saddlepoint solution of the Euclidean action describing the
simultaneous decay of the phases in all the junctions. When the current is
reduced, a crossover to a regime takes place, where the decay occurs via an
"elastic" saddlepoint solution and the phases across the junctions leave the
metastable state one after another. This leads to an increased decay rate
compared with the rigid case both in the thermal and the quantum regime. The
rigid-to-elastic crossover can be sharp or smooth analogous to first- or
second- order phase transitions, respectively. The various regimes are
summarized in a current-temperature decay diagram.Comment: 11 pages, RevTeX, 3 PS-figures, revised versio
Critical generalized inverse participation ratio distributions
The system size dependence of the fluctuations in generalized inverse
participation ratios (IPR's) at criticality is investigated
numerically. The variances of the IPR logarithms are found to be
scale-invariant at the macroscopic limit. The finite size corrections to the
variances decay algebraically with nontrivial exponents, which depend on the
Hamiltonian symmetry and the dimensionality. The large- dependence of the
asymptotic values of the variances behaves as according to theoretical
estimates. These results ensure the self-averaging of the corresponding
generalized dimensions.Comment: RevTex4, 5 pages, 4 .eps figures, to be published in Phys. Rev.
Functional Dissection of the Proton Pumping Modules of Mitochondrial Complex I
A catalytically active subcomplex of respiratory chain complex I lacks 14 of its 42 subunits yet retains half of its proton-pumping capacity, indicating that its membrane arm has two pump modules
Magnetic Field Effect for Two Electrons in a Two Dimensional Random Potential
We study the problem of two particles with Coulomb repulsion in a
two-dimensional disordered potential in the presence of a magnetic field. For
the regime, when without interaction all states are well localized, it is shown
that above a critical excitation energy electron pairs become delocalized by
interaction. The transition between the localized and delocalized regimes goes
in the same way as the metal-insulator transition at the mobility edge in the
three dimensional Anderson model with broken time reversal symmetry.Comment: revtex, 7 pages, 6 figure
Transition to an Insulating Phase Induced by Attractive Interactions in the Disordered Three-Dimensional Hubbard Model
We study numerically the interplay of disorder and attractive interactions
for spin-1/2 fermions in the three-dimensional Hubbard model. The results
obtained by projector quantum Monte Carlo simulations show that at moderate
disorder, increasing the attractive interaction leads to a transition from
delocalized superconducting states to the insulating phase of localized pairs.
This transition takes place well within the metallic phase of the
single-particle Anderson model.Comment: revtex, 4 pages, 3 figure
Crossovers in the thermal decay of metastable states in discrete systems
The thermal decay of linear chains from a metastable state is investigated. A
crossover from rigid to elastic decay occurs when the number of particles, the
single particle energy barrier or the coupling strength between the particles
is varied. In the rigid regime, the single particle energy barrier is small
compared to the coupling strength and the decay occurs via a uniform
saddlepoint solution, with all degrees of freedom decaying instantly.
Increasing the barrier one enters the elastic regime, where the decay is due to
bent saddlepoint configurations using the elasticity of the chain to lower
their activation energy. Close to the rigid-to-elastic crossover, nucleation
occurs at the boundaries of the system. However, in large systems, a second
crossover from boundary to bulk nucleation can be found within the elastic
regime, when the single particle energy barrier is further increased. We
compute the decay rate in the rigid and in the elastic regimes within the
Gaussian approximation. Around the rigid-to-elastic crossover, the calculations
are performed beyond the steepest descent approximation. In this region, the
prefactor exhibits a scaling property. The theoretical results are discussed in
the context of discrete Josephson transmission lines and pancake vortex stacks
that are pinned by columnar defects.Comment: 13 pages, RevTeX, 7 PS-figure
Phase diagram of localization in a magnetic field
The phase diagram of localization is numerically calculated for a
three-dimensional disordered system in the presence of a magnetic field using
the Peierls substitution. The mobility edge trajectory shifts in the
energy-disorder space when increasing the field. In the band center, localized
states near the phase boundary become delocalized. The obtained field
dependence of the critical disorder is in agreement with a power law behavior
expected from scaling theory. Close to the tail of the band the magnetic field
causes localization of extended states.Comment: 4 pages, RevTeX, 3 PS-figures (4 extra references are included, minor
additions), to appear in Phys. Rev. B as a Brief Repor
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