1,837 research outputs found
Interchain Coupling Effects and Solitons in CuGeO_3
The effects of interchain coupling on solitons and soliton lattice structures
in CuGeO3 are explored. It is shown that interchain coupling substantially
increases the soliton width and changes the soliton lattice structures in the
incommensurate phase. It is proposed that the experimentally observed large
soliton width in CuGeO3 is mainly due to interchain coupling effects.Comment: 4 pages, LaTex, one eps figure included. No essential changes except
forma
Measurements of Temperature of the Different Parts of a Radio Receiver and of the Oscillator Drift During Warming
Chaotic quantum dots with strongly correlated electrons
Quantum dots pose a problem where one must confront three obstacles:
randomness, interactions and finite size. Yet it is this confluence that allows
one to make some theoretical advances by invoking three theoretical tools:
Random Matrix theory (RMT), the Renormalization Group (RG) and the 1/N
expansion. Here the reader is introduced to these techniques and shown how they
may be combined to answer a set of questions pertaining to quantum dotsComment: latex file 16 pages 8 figures, to appear in Reviews of Modern Physic
An explanation for a universality of transition temperatures in families of copper oxide superconductors
A remarkable mystery of the copper oxide high-transition-temperature (Tc)
superconductors is the dependence of Tc on the number of CuO2 layers, n, in the
unit cell of a crystal. In a given family of these superconductors, Tc rises
with the number of layers, reaching a peak at n=3, and then declines: the
result is a bell-shaped curve. Despite the ubiquity of this phenomenon, it is
still poorly understood and attention has instead been mainly focused on the
properties of a single CuO2 plane. Here we show that the quantum tunnelling of
Cooper pairs between the layers simply and naturally explains the experimental
results, when combined with the recently quantified charge imbalance of the
layers and the latest notion of a competing order nucleated by this charge
imbalance that suppresses superconductivity. We calculate the bell-shaped curve
and show that, if materials can be engineered so as to minimize the charge
imbalance as n increases, Tc can be raised further.Comment: 15 pages, 3 figures. The version published in Natur
Effects of antiferromagnetic planes on the superconducting properties of multilayered high-Tc cuprates
We propose a mechanism for high critical temperature (T_c) in the coexistent
phase of superconducting- (SC) and antiferromagnetic (AF) CuO_2 planes in
multilayered cuprates. The Josephson coupling between the SC planes separated
by an AF insulator (Mott insulator) is calculated perturbatively up to the
fourth order in terms of the hopping integral between adjacent CuO_2 planes. It
is shown that the AF exchange splitting in the AF plane suppresses the
so-called pi-Josephson coupling, and the long-ranged 0-Josephson coupling leads
to coexistence with a rather high value of T_c.Comment: 4 pages including 4 figure
The nature and boundary of the floating phase in a dissipative Josephson junction array
We study the nature of correlations within, and the transition into, the
floating phase of dissipative Josephson junction arrays. Order parameter
correlations in this phase are long-ranged in time, but only short-ranged in
space. A perturbative RG analysis shows that, in {\it arbitrary} spatial
dimension, the transition is controlled by a continuous locus of critical fixed
points determined entirely by the \textit{local} topology of the lattice. This
may be the most natural example of a line of critical points existing in
arbitrary dimensions.Comment: Parts rewritten, typos correcte
Ginzburg-Landau Expansion and the Slope of the Upper Critical Field in Disordered Superconductors with Anisotropic Pairing
It is demonstrated that the slope of the upper critical field
in superconductors with -wave pairing drops rather
fast with concentration of normal impurities, while in superconductors with
anisotropic -wave pairing grows, and in the limit of
strong disorder is described by the known dependences of the theory of
``dirty'' superconductors. This allows to use the measurements of in
disordered superconductors to discriminate between these different types of
pairing in high-temperature and heavy-fermion superconductors.Comment: 7 pages, 5 figures, RevTeX 3.0, 4 Postscript figures attached;
Submitted to JETP Letter
Quantum oscillations in graphene in the presence of disorder and interactions
Quantum oscillations in graphene is discussed. The effect of interactions are
addressed by Kohn's theorem regarding de Haas-van Alphen oscillations, which
states that electron-electron interactions cannot affect the oscillation
frequencies as long as disorder is neglected and the system is sufficiently
screened, which should be valid for chemical potentials not very close to the
Dirac point. We determine the positions of Landau levels in the presence of
potential disorder from exact transfer matrix and finite size diagonalization
calculations. The positions are shown to be unshifted even for moderate
disorder; stronger disorder, can, however, lead to shifts, but this also
appears minimal even for disorder width as large as one-half of the bare
hopping matrix element on the graphene lattice. Shubnikov-de Haas oscillations
of the conductivity are calculated analytically within a self-consistent Born
approximation of impurity scattering. The oscillatory part of the conductivity
follows the widely invoked Lifshitz-Kosevich form when certain mass and
frequency parameters are properly interpreted.Comment: Appendix A was removed, as the content of it is already contained in
Ref. 17. Thanks to M. A. H. Vozmedian
NMR relaxation in half-integer antiferromagnetic spin chains
Nuclear relaxation in half-integer spin chains at low temperatures (T << J,
the antiferromagnetic exchange constant) is dominated by dissipation from a gas
of thermally-excited, overdamped, spinons. The universal low temperature
dependence of the relaxation rates and is computed.Comment: 7 pages, 1 uuencoded postscript figure appende
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