385 research outputs found
Specific heat of aluminium-doped superconducting silicon carbide
The discoveries of superconductivity in heavily boron-doped diamond, silicon
and silicon carbide renewed the interest in the ground states of charge-carrier
doped wide-gap semiconductors. Recently, aluminium doping in silicon carbide
successfully yielded a metallic phase from which at high aluminium
concentrations superconductivity emerges. Here, we present a specific-heat
study on superconducting aluminium-doped silicon carbide. We observe a clear
jump anomaly at the superconducting transition temperature 1.5 K indicating
that aluminium-doped silicon carbide is a bulk superconductor. An analysis of
the jump anomaly suggests BCS-like phonon-mediated superconductivity in this
system.Comment: 4 pages, 2 figure
Superconductivity of hexagonal heavily-boron doped silicon carbide
In 2004 the discovery of superconductivity in heavily boron-doped diamond
(C:B) led to an increasing interest in the superconducting phases of wide-gap
semiconductors. Subsequently superconductivity was found in heavily boron-doped
cubic silicon (Si:B) and recently in the stochiometric ''mixture'' of heavily
boron-doped silicon carbide (SiC:B). The latter system surprisingly exhibits
type-I superconductivity in contrast to the type-II superconductors C:B and
Si:B. Here we will focus on the specific heat of two different superconducting
samples of boron-doped SiC. One of them contains cubic and hexagonal SiC
whereas the other consists mainly of hexagonal SiC without any detectable cubic
phase fraction. The electronic specific heat in the superconducting state of
both samples SiC:B can be described by either assuming a BCS-type exponentional
temperature dependence or a power-law behavior.Comment: 4 pages, 1 figure
Superconductivity in heavily boron-doped silicon carbide
The discoveries of superconductivity in heavily boron-doped diamond (C:B) in
2004 and silicon (Si:B) in 2006 renew the interest in the superconducting state
of semiconductors. Charge-carrier doping of wide-gap semiconductors leads to a
metallic phase from which upon further doping superconductivity can emerge.
Recently, we discovered superconductivity in a closely related system:
heavily-boron doped silicon carbide (SiC:B). The sample used for that study
consists of cubic and hexagonal SiC phase fractions and hence this lead to the
question which of them participates in the superconductivity. Here we focus on
a sample which mainly consists of hexagonal SiC without any indication for the
cubic modification by means of x-ray diffraction, resistivity, and ac
susceptibility.Comment: 9 pages, 5 figure
Apparent finite-size effects in the dynamics of supercooled liquids
Molecular dynamics simulations are performed for a supercooled simple liquid
with changing the system size from N=108 to to examine possible
finite-size effects. Although almost no systematic deviation is detected in the
static pair correlation functions, it is demonstrated that the structural
relaxation in a small system becomes considerably slower than that in
larger systems for temperatures below at which the size of the
cooperative particle motions becomes comparable to the unit cell length of the
small system. The discrepancy increases with decreasing temperature.Comment: 4 pages 5 figure
Kinetic Heterogeneities in a Highly Supercooled Liquid
We study a highly supercooled two-dimensional fluid mixture via molecular
dynamics simulation. We follow bond breakage events among particle pairs, which
occur on the scale of the relaxation time . Large scale
heterogeneities analogous to the critical fluctuations in Ising systems are
found in the spatial distribution of bonds which are broken in a time interval
with a width of order . The structure factor of the broken
bond density is well approximated by the Ornstein-Zernike form. The correlation
length is of order at the lowest temperature studied,
being the particle size. The weakly bonded regions thus identified evolve in
time with strong spatial correlations.Comment: 3 pages, 6 figure
Anisotropic s-wave superconductivity in single crystals CaAlSi from penetration depth measurements
In- and out-of-plane London penetration depths were measured in single
crystals CaAlSi (T_{c}=6.2 K and 7.3 K) using a tunnel-diode resonator. A full
3D BCS analysis of the superfluid density is consistent with a prolate
spheroidal gap, with a weak-coupling BCS value in the ab-plane and stronger
coupling along the c-axis. The gap anisotropy was found to significantly
decrease for higher T_{c} samples.Comment: 4 page
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