56,796 research outputs found
Symmetry of the Gap in Bi2212 from Photoemission Spectroscopy
In a recent Letter, Shen et al have detected a large anisotropy of the
superconducting gap in Bi2212, consistent with d-wave symmetry, from
photoemission spectroscopy. Moreover, they claim that the change in their
spectra as a function of aging is also consistent with such an intrepretation.
In this Comment, I show that the latter statement is not entirely correct, in
that the data as a function of aging are inconsistent with a d-wave gap but are
consistent with an anisotropic s-wave gap.Comment: 3 pages (Plain TeX with macros), plus 1 postscript figur
Calibration of shielded microwave probes using bulk dielectrics
A stripline-type near-field microwave probe is microfabricated for microwave
impedance microscopy. Unlike the poorly shielded coplanar probe that senses the
sample tens of microns away, the stripline structure removes the stray fields
from the cantilever body and localizes the interaction only around the
focused-ion beam deposited Pt tip. The approaching curve of an oscillating tip
toward bulk dielectrics can be quantitatively simulated and fitted to the
finite-element analysis result. The peak signal of the approaching curve is a
measure of the sample dielectric constant and can be used to study unknown bulk
materials.Comment: 10 pages, 3 figure
Two-terminal monolithic InP-based tandem solar cells with tunneling intercell ohmic connections
A monolithic two-terminal InP/InGaAsP tandem solar cell was successfully fabricated. This tandem solar cell consists of a p/n InP homojunction top subcell and a 0.95 eV p/n InGaAsP homojunction bottom subcell. A patterned 0.95 eV n(+)/p(+) InGaAsP tunnel diode was employed as an intercell ohmic connection. The solar cell structure was prepared by two-step liquid phase epitaxial growth. Under one sun, AM1.5 global illumination, the best tandem cell delivered a conversion efficiency of 14.8 pct
Magnetic anisotropy switching in (Ga,Mn)As with increasing hole concentration
We study a possible mechanism of the switching of the magnetic easy axis as a
function of hole concentration in (Ga,Mn)As epilayers. In-plane uniaxial
magnetic anisotropy along [110] is found to exceed intrinsic cubic
magnetocrystalline anisotropy above a hole concentration of p = 1.5 * 10^21
cm^-3 at 4 K. This anisotropy switching can also be realized by post-growth
annealing, and the temperature-dependent ac susceptibility is significantly
changed with increasing annealing time. On the basis of our recent scenario
[Phys. Rev. Lett. 94, 147203 (2005); Phys. Rev. B 73, 155204 (2006).], we
deduce that the growth of highly hole-concentrated cluster regions with [110]
uniaxial anisotropy is likely the predominant cause of the enhancement in [110]
uniaxial anisotropy at the high hole concentration regime. We can clearly rule
out anisotropic lattice strain as a possible origin of the switching of the
magnetic anisotropy.Comment: 5 pages, 4 figures, to appear in Phys. Rev.
Thermo-acoustic wave propagation and reflection near the liquid-gas critical point
We study the thermo-acoustic wave propagation and reflection near the
liquid-gas critical point. Specifically, we perform a numerical investigation
of the acoustic responses in a near-critical fluid to thermal perturbations
based on the same setup of a recent ultrasensitive interferometry measurement
in CO2 [Y. Miura et al. Phys. Rev. E 74, 010101(R) (2006)]. The numerical
results agree well with the experimental data. New features regarding the
reflection pattern of thermo-acoustic waves near the critical point under pulse
perturbations are revealed by the proper inclusion of the critically diverging
bulk viscosity.Comment: 14 pages, 4 figures, Accepted by PRE (Rapid Communication
A competing order scenario of two-gap behavior in hole doped cuprates
Angle-dependent studies of the gap function provide evidence for the
coexistence of two distinct gaps in hole doped cuprates, where the gap near the
nodal direction scales with the superconducting transition temperature ,
while that in the antinodal direction scales with the pseudogap temperature. We
present model calculations which show that most of the characteristic features
observed in the recent angle-resolved photoemission spectroscopy (ARPES) as
well as scanning tunneling microscopy (STM) two-gap studies are consistent with
a scenario in which the pseudogap has a non-superconducting origin in a
competing phase. Our analysis indicates that, near optimal doping,
superconductivity can quench the competing order at low temperatures, and that
some of the key differences observed between the STM and ARPES results can give
insight into the superlattice symmetry of the competing order.Comment: 9 pages, 7 fig
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