23,215 research outputs found
Paramagnetic state in d-wave Superconductors
We study theoretically the paramagnetic state in d-wave superconductors. We
present the specific heat, the magnetization, superfluid density obtained
within the weak-coupling model. At low temperatures and for small magnetic
fields they exhibit simple power law behaviors, which should be accessible
experimentally in hole-doped high-T_c cuprates and \kappa-(ET)_2 salts in a
magnetic field within the conducting plane.Comment: 5 pages(EuroTeX), 13 figures, submitted to Europhysics Letter
Folding thermodynamics of model four-strand antiparallel beta-sheet proteins
The thermodynamic properties for three different types of off-lattice
four-strand beta-sheet protein models interacting via a hybrid Go-type
potential have been investigated. Discontinuous molecular dynamic simulations
have been performed for different sizes of the bias gap g, an artificial
measure of a model protein's preference for its native state. The thermodynamic
transition temperatures are obtained by calculating the squared radius of
gyration, the root-mean-squared pair separation fluctuation, the specific heat,
the internal energy of the system, and the Lindemann disorder parameter. In
spite of the simplicity, the protein-like heteropolymers have shown a complex
set of protein transitions as observed in experimental studies. Starting from
high temperature, these transitions include a collapse transition, a
disordered-to-ordered globule transition, a folding transition, and a
liquid-to-solid transition. These transitions strongly depend on the
native-state geometry of the model proteins and the size of the bias gap. A
strong transition from the disordered globule state to the ordered globule
state with large energy change and a weak transition from the ordered globule
state to the native state with small energy change were observed for the large
gap models. For the small gap models no native structures were observed at any
temperature, all three beta-sheet proteins fold into a partially-ordered
globule state which is geometrically different from the native state. For small
bias gaps at even lower temperatures, all protein motions are frozen indicating
an inactive solid-like phase.Comment: PDF file, 32 pages including 13 figure page
Observation of dispersive wave emission by temporal cavity solitons
We examine a coherently-driven, dispersion-managed, passive Kerr fiber ring
resonator and report the first direct experimental observation of dispersive
wave emission by temporal cavity solitons. Our observations are in excellent
agreement with analytical predictions and they are fully corroborated by
numerical simulations. These results lead to a better understanding of the
behavior of temporal cavity solitons under conditions where higher-order
dispersion plays a significant role. Significantly, since temporal cavity
solitons manifest themselves in monolithic microresonators, our results are
likely to explain the origins of spectral features observed in broadband Kerr
frequency combs.Comment: 4 pages, 3 figure
Surface segregation and the Al problem in GaAs quantum wells
Low-defect two-dimensional electron systems (2DESs) are essential for studies
of fragile many-body interactions that only emerge in nearly-ideal systems. As
a result, numerous efforts have been made to improve the quality of
modulation-doped AlGaAs/GaAs quantum wells (QWs), with an emphasis
on purifying the source material of the QW itself or achieving better vacuum in
the deposition chamber. However, this approach overlooks another crucial
component that comprises such QWs, the AlGaAs barrier. Here we show
that having a clean Al source and hence a clean barrier is instrumental to
obtain a high-quality GaAs 2DES in a QW. We observe that the mobility of the
2DES in GaAs QWs declines as the thickness or Al content of the
AlGaAs barrier beneath the QW is increased, which we attribute to
the surface segregation of Oxygen atoms that originate from the Al source. This
conjecture is supported by the improved mobility in the GaAs QWs as the Al cell
is cleaned out by baking
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