48,052 research outputs found
Close-packed structures and phase diagram of soft spheres in cylindrical pores
It is shown for a model system consisting of spherical particles confined in cylindrical pores that the first ten close-packed phases are in one-to-one correspondence with the first ten ways of folding a triangular lattice, each being characterized by a roll-up vector like the single-walled carbon nanotube. Phase diagrams in pressure-diameter and temperature-diameter planes are obtained by inherent-structure calculation and molecular dynamics simulation. The phase boundaries dividing two adjacent phases are infinitely sharp in the low-temperature limit but are blurred as temperature is increased. Existence of such phase boundaries explains rich, diameter-sensitive phase behavior unique for cylindrically confined systems
Interference Effects on Kondo-Assisted Transport through Double Quantum Dots
We systematically investigate electron transport through double quantum dots
with particular emphasis on interference induced via multiple paths of electron
propagation. By means of the slave-boson mean-field approximation, we calculate
the conductance, the local density of states, the transmission probability in
the Kondo regime at zero temperature. It is clarified how the Kondo-assisted
transport changes its properties when the system is continuously changed among
the serial, parallel and T-shaped double dots. The obtained results for the
conductance are explained in terms of the Kondo resonances influenced by
interference effects. We also discuss the impacts due to the spin-polarization
of ferromagnetic leads.Comment: 9 pages, 11 figures ; minor corrections and references adde
A Viscoelastic model of phase separation
We show here a general model of phase separation in isotropic condensed
matter, namely, a viscoelastic model. We propose that the bulk mechanical
relaxation modulus that has so far been ignored in previous theories plays an
important role in viscoelastic phase separation in addition to the shear
relaxation modulus. In polymer solutions, for example, attractive interactions
between polymers under a poor-solvent condition likely cause the transient
gellike behavior, which makes both bulk and shear modes active. Although such
attractive interactions between molecules of the same component exist
universally in the two-phase region of a mixture, the stress arising from
attractive interactions is asymmetrically divided between the components only
in dynamically asymmetric mixtures such as polymer solutions and colloidal
suspensions. Thus, the interaction network between the slower components, which
can store the elastic energy against its deformation through bulk and shear
moduli, is formed. It is the bulk relaxation modulus associated with this
interaction network that is primarily responsible for the appearance of the
sponge structure peculiar to viscoelastic phase separation and the phase
inversion. We demonstrate that a viscoelastic model of phase separation
including this new effect is a general model that can describe all types of
isotropic phase separation including solid and fluid models as its special
cases without any exception, if there is no coupling with additional order
parameter. The physical origin of volume shrinking behavior during viscoelastic
phase separation and the universality of the resulting spongelike structure are
also discussed.Comment: 14 pages, RevTex, To appear in Phys. Rev
Strong magnetic field enhancement of spin triplet pairing arising from coexisting spin and charge fluctuations
We study the effect of the magnetic field (Zeeman splitting) on the triplet
pairing. We show generally that the enhancement of spin triplet pairing
mediated by coexisting spin and charge fluctuations can be much
larger than in the case of triplet pairing mediated by ferromagnetic spin
fluctuations. We propose that this may be related to the recent experiment for
(TMTSF)ClO, in which a possibility of singlet to triplet pairing
transition has been suggested.Comment: 5 page
Nonlinear Pseudo-Supersymmetry in the Framework of N-fold Supersymmetry
We recall the importance of recognizing the different mathematical nature of
various concepts relating to PT-symmetric quantum theories. After clarifying
the relation between supersymmetry and pseudo-supersymmetry, we prove
generically that nonlinear pseudo-supersymmetry, recently proposed by Sinha and
Roy, is just a special case of N-fold supersymmetry. In particular, we show
that all the models constructed by these authors have type A 2-fold
supersymmetry. Furthermore, we prove that an arbitrary one-body quantum
Hamiltonian which admits two (local) solutions in closed form belongs to type A
2-fold supersymmetry, irrespective of whether or not it is Hermitian,
PT-symmetric, pseudo-Hermitian, and so on.Comment: 10 pages, no figures; typos correcte
Correlated electron transport through double quantum dots coupled to normal and superconducting leads
We study Andreev transport through double quantum dots connected in series
normal and superconducting (SC) leads, using the numerical renormalization
group. The ground state of this system shows a crossover between a local
Cooper-pairing singlet state and a Kondo singlet state, which is caused by the
competition between the Coulomb interaction and the SC proximity. We show that
the ground-state properties reflect this crossover especially for small values
of the inter-dot coupling , while in the opposite case, for large ,
another singlet with an inter-dot character becomes dominant. We find that the
conductance for the local SC singlet state has a peak with the unitary-limit
value . In contrast, the Andreev reflection is suppressed in the Kondo
regime by the Coulomb interaction. Furthermore, the conductance has two
successive peaks in the transient region of the crossover. It is further
elucidated that the gate voltage gives a different variation into the
crossover. Specifically, as the energy level of the dot that is coupled to the
normal lead varies, the Kondo screening cloud is deformed to a long-range
singlet bond.Comment: 11 pages, 10 figure
Pairing Symmetry of CeCoIn Detected by In-plane Torque Measurements
In-plane torque measurements were performed on heavy fermion CeCoIn
single crystals in the temperature range 1.8 K K and
applied magnetic field up to 14 T. The normal-state torque is given by
. The reversible part of the
mixed-state torque, obtained after subtracting the corresponding normal state
torque, shows also a four-fold symmetry. In addition, sharp peaks are present
in the irreversible torque at angles of 4, 3/4, 5/4, 7/4,
etc. Both the four-fold symmetry in the reversible torque and the sharp peaks
in the irreversible torque of the mixed state imply symmetry of the
superconducting order parameter. The field and temperature dependences of the
reversible mixed-state torque provide further evidence for wave
symmetry. The four-fold symmetry in the normal state has a different origin
since it has different field and temperature dependences than the one in the
mixed state. The possible reasons of the normal state four-fold symmetry are
discussed
Cosmic censorship in overcharging a Reissner-Nordstr\"{o}m black hole via charged particle absorption
There is a claim that a static charged black hole (Reissner-Nordstr\"{o}m
black hole) can be overcharged by absorbing a charged test particle. If it is
true, it might give a counter example to the weak cosmic censorship conjecture,
which states that spacetime singularities are never observed by a distant
observer. However, so far the proposed process has only been analyzed within a
test particle approximation. Here we claim that the back reaction effects of a
charged particle cannot be neglected when judging whether the suggested process
is really a counter example to the cosmic censorship conjecture or not.
Furthermore, we argue that all the back reaction effects can be properly taken
into account when we consider the trajectory of a particle on the border
between the plunge and bounce orbits. In such marginal cases we find that the
Reissner-Nordstr\"{o}m black hole can never be overcharged via the absorption
of a charged particle. Since all the plunge orbits are expected to have a
higher energy than the marginal orbit, we conclude that there is no supporting
evidence that indicates the violation of the cosmic censorship in the proposed
overcharging process.Comment: 18 pages, revtex4, minor revision and reference added, version to
appear in PR
On broad iron K-alpha lines in Seyfert 1 galaxies
The X-ray spectrum obtained by Tanaka et al from a long observation of the
active galaxy MCG shows a broad iron K line skewed to low
energies. The simplest interpretation of the shape of the line is that it is
due to doppler and gravitational redshifts from the inner parts of a disk about
a massive black hole. Similarly broad lines are evident in shorter observations
of several other active galaxies. In this paper we investigate other line
broadening and skewing mechanisms such as Comptonization in cold gas and
doppler shifts from outflows. We have also fitted complex spectral models to
the data of MCG to see whether the broad skewed line can be mimicked
well by other absorption or emission features. No satisfactory mechanism or
spectral model is found, thus strengthening the relativistic disk line model.Comment: uuencoded compressed postscript. The preprint is also available at
http://www.ast.cam.ac.uk/preprint/PrePrint.htm
Angular dependence of Josephson currents in unconventional superconducting junctions
Josephson effect in junctions between unconventional superconductors is
studied theoretically within the model describing the effects of interface
roughness. The particularly important issue of applicability of the frequently
used Sigrist-Rice formula for Josephson current in d-wave superconductor /
insulator / d-wave superconductor junctions is addressed. We show that although
the SR formula is not applicable in the ballistic case, it works well for rough
interfaces when the diffusive normal metal regions exist between the d-wave
superconductor and the insulator. It is shown that the SR approach only takes
into account the component of the d-wave pair potential symmetric with respect
to an inversion around the plane perpendicular to the interface. Similar
formula can be derived for general unconventional superconductors with
arbitrary angular momentum l.Comment: 4 pages, 4 figure
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