8,696 research outputs found
Possible indicators for low dimensional superconductivity in the quasi-1D carbide Sc3CoC4
The transition metal carbide Sc3CoC4 consists of a quasi-one-dimensional (1D)
structure with [CoC4]_{\inft} polyanionic chains embedded in a scandium
matrix. At ambient temperatures Sc3CoC4 displays metallic behavior. At lower
temperatures, however, charge density wave formation has been observed around
143K which is followed by a structural phase transition at 72K. Below T^onset_c
= 4.5K the polycrystalline sample becomes superconductive. From Hc1(0) and
Hc2(0) values we could estimate the London penetration depth ({\lambda}_L ~=
9750 Angstroem) and the Ginsburg-Landau (GL) coherence length ({\xi}_GL ~= 187
Angstroem). The resulting GL-parameter ({\kappa} ~= 52) classifies Sc3CoC4 as a
type II superconductor. Here we compare the puzzling superconducting features
of Sc3CoC4, such as the unusual temperature dependence i) of the specific heat
anomaly and ii) of the upper critical field H_c2(T) at T_c, and iii) the
magnetic hysteresis curve, with various related low dimensional
superconductors: e.g., the quasi-1D superconductor (SN)_x or the 2D
transition-metal dichalcogenides. Our results identify Sc3CoC4 as a new
candidate for a quasi-1D superconductor.Comment: 4 pages, 5 figure
Quantum dot photonic crystal lasers
Coupled cavity designs on two-dimensional square lattice photonic crystal slabs were used to demonstrate optically pumped indium arsenide quantum dot photonic crystal lasers at room temperature. Threshold pump powers of 120 and 370 μW were observed for coupled cavities including two and four defect cavities defined in optimised photonic crystals
Three-dimensional macroporous silicon photonic crystal with large photonic band gap
Three-dimensional photonic crystals based on macroporous silicon are fabricated by photoelectrochemical etching and subsequent focused-ion-beam drilling. Reflection measurements show a high reflection in the range of the stopgap and indicate the spectral position of the complete photonic band gap. The onset of diffraction which might influence the measurement is discussed
Fabrication of small laterally patterned multiple quantum wells
A technique of high voltage electron beam lithography and BCI_3/Ar reactive ion etching for laterally patterning GaAs/Al_0_3 Ga_(0.7) As multiple quantum wells is described. The resulting structures were analyzed using scanning electron microscopy and a novel reflection electron microscopy technique, and their geometries are shown. Narrow columns 40 nm in diameter etched 230 nm through the quantum wells were reproducibly fabricated
Characterization of Alkali Metal Dispensers and Non-Evaporable Getter Pumps in Ultra-High Vacuum Systems for Cold Atomic Sensors
A glass ultrahigh vacuum chamber with rubidium alkali metal dispensers and
non-evaporable getter pumps has been developed and used to create a cold atomic
sample in a chamber that operates with only passive vacuum pumps. The ion-mass
spectrum of evaporated gases from the alkali metal dispenser has been recorded
as a function of dispenser current. The efficacy of the non-evaporable getter
pumps in promoting and maintaining vacuum has been characterized by observation
of the Rb vapor optical absorption on the D2 transition at 780 nm and vacuum
chamber pressure rate of rise tests. We have demonstrated a sample of
laser-cooled Rb atoms in this chamber when isolated and operating without
active vacuum pumps
Functional renormalization and mean-field approach to multiband systems with spin-orbit coupling: Application to the Rashba model with attractive interaction
The functional renormalization group (RG) in combination with Fermi surface
patching is a well-established method for studying Fermi liquid instabilities
of correlated electron systems. In this article, we further develop this method
and combine it with mean-field theory to approach multiband systems with
spin-orbit coupling, and we apply this to a tight-binding Rashba model with an
attractive, local interaction. The spin dependence of the interaction vertex is
fully implemented in a RG flow without SU(2) symmetry, and its momentum
dependence is approximated in a refined projection scheme. In particular, we
discuss the necessity of including in the RG flow contributions from both bands
of the model, even if they are not intersected by the Fermi level. As the
leading instability of the Rashba model, we find a superconducting phase with a
singlet-type interaction between electrons with opposite momenta. While the gap
function has a singlet spin structure, the order parameter indicates an
unconventional superconducting phase, with the ratio between singlet and
triplet amplitudes being plus or minus one on the Fermi lines of the upper or
lower band, respectively. We expect our combined functional RG and mean-field
approach to be useful for an unbiased theoretical description of the
low-temperature properties of spin-based materials.Comment: consistent with published version in Physical Review B (2016
Generalized polarizabilities and the spin-averaged amplitude in virtual Compton scattering off the nucleon
We discuss the low-energy behavior of the spin-averaged amplitude of virtual
Compton scattering (VCS) off a nucleon.
Based on gauge invariance, Lorentz invariance and the discrete symmetries, it
is shown that to first order in the frequency of the final real photon only two
generalized polarizabilities appear.
Different low-energy expansion schemes are discussed and put into
perspective.Comment: 13 pages, 1 postscript figure, Revtex using eps
A practical mode system for recursive definitions
In call-by-value languages, some mutually-recursive value definitions can be
safely evaluated to build recursive functions or cyclic data structures, but
some definitions (let rec x = x + 1) contain vicious circles and their
evaluation fails at runtime. We propose a new static analysis to check the
absence of such runtime failures.
We present a set of declarative inference rules, prove its soundness with
respect to the reference source-level semantics of Nordlander, Carlsson, and
Gill (2008), and show that it can be (right-to-left) directed into an
algorithmic check in a surprisingly simple way.
Our implementation of this new check replaced the existing check used by the
OCaml programming language, a fragile syntactic/grammatical criterion which let
several subtle bugs slip through as the language kept evolving. We document
some issues that arise when advanced features of a real-world functional
language (exceptions in first-class modules, GADTs, etc.) interact with safety
checking for recursive definitions
Kovacs effects in an aging molecular liquid
We study by means of molecular dynamics simulations the aging behavior of a
molecular model of ortho-terphenyl. We find evidence of a a non-monotonic
evolution of the volume during an isothermal-isobaric equilibration process, a
phenomenon known in polymeric systems as Kovacs effect. We characterize this
phenomenology in terms of landscape properties, providing evidence that, far
from equilibrium, the system explores region of the potential energy landscape
distinct from the one explored in thermal equilibrium. We discuss the relevance
of our findings for the present understanding of the thermodynamics of the
glass state.Comment: RevTeX 4, 4 pages, 5 eps figure
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