3,361 research outputs found
Superconductivity in Pseudo-Binary Silicide SrNixSi2-x with AlB2-Type Structure
We demonstrate the emergence of superconductivity in pseudo-binary silicide
SrNixSi2-x. The compound exhibits a structural phase transition from the cubic
SrSi2-type structure (P4132) to the hexagonal AlB2-type structure (P6/mmm) upon
substituting Ni for Si at approximately x = 0.1. The hexagonal structure is
stabilized in the range of 0.1 < x < 0.7. The superconducting phase appears in
the vicinity of the structural phase boundary. Ni acts as a nonmagnetic dopant,
as confirmed by the Pauli paramagnetic behavior.Comment: 12 pages, 5 figure
Non-diffracting Optical Beams in a Three-level Raman System
Diffractionless propagation of optical beams through atomic vapors is
investigated. The atoms in the vapor are operated in a three-level Raman
configuration. A suitably chosen control beam couples to one of the
transitions, and thereby creates a spatially varying index of refraction
modulation in the warm atomic vapor for a probe beam which couples to the other
transition in the atoms. We show that a Laguerre-Gaussian control beam allows
to propagate single Gaussian probe field modes as well as multi-Gaussian modes
and non-Gaussian modes over macroscopic distances without diffraction. This
opens perspectives for the propagation of arbitrary images through warm atomic
vapors.Comment: 8 pages, 7 figure
Piece by Piece-Electrochemical Synthesis of Individual Nanoparticles and their Performance in ORR Electrocatalysis
The impact of individual HAuCl4 nanoreactors is measured electrochemically, which provides operando insights and precise control over the modification of electrodes with functional nanoparticles of wellâdefined size. Uniformly sized micelles are loaded with a dissolved metal salt. These solutionâphase precursor entities are then reduced electrochemicallyâone by oneâto form nanoparticles (NPs). The charge transferred during the reduction of each micelle is measured individually and allows operando sizing of each of the formed nanoparticles. Thus, particles of known number and sizes can be deposited homogenously even on nonplanar electrodes. This is demonstrated for the decoration of cylindrical carbon fibre electrodes with 25±7â
nm sized Au particles from HAuCl4âfilled micelles. These Au NPâdecorated electrodes show great catalyst performance for ORR (oxygen reduction reaction) already at low catalyst loadings. Hence, collisions of individual precursorâfilled nanocontainers are presented as a new route to nanoparticleâmodified electrodes with high catalyst utilization
Griffiths phase in the thermal quantum Hall effect
Two dimensional disordered superconductors with broken spin-rotation and
time-reversal invariance, e.g. with p_x+ip_y pairing, can exhibit plateaus in
the thermal Hall coefficient (the thermal quantum Hall effect). Our numerical
simulations show that the Hall insulating regions of the phase diagram can
support a sub-phase where the quasiparticle density of states is divergent at
zero energy, \rho(E)\sim |E|^{1/z-1}, with a non-universal exponent , due
to the effects of rare configurations of disorder (``Griffiths phase'').Comment: 4+ pages, 5 figure
Measuring perceived adaptiveness in a robotic eldercare companion
Based on observations in previous experiments with a robotic companion in eldercare and on findings in related literature, we developed the concept of Perceived Adaptiveness. We integrated this in our technology acceptance methodology for robotic eldercare companions and found in a small experiment that adaptiveness of the system as perceived by elderly users is indeed a relevant item, being a direct influence on Perceived Usefulness
Multifractality of wavefunctions at the quantum Hall transition revisited
We investigate numerically the statistics of wavefunction amplitudes
at the integer quantum Hall transition. It is demonstrated that
in the limit of a large system size the distribution function of is
log-normal, so that the multifractal spectrum is exactly parabolic.
Our findings lend strong support to a recent conjecture for a critical theory
of the quantum Hall transition.Comment: 4 pages Late
Universal time-evolution of a Rydberg lattice gas with perfect blockade
We investigate the dynamics of a strongly interacting spin system that is
motivated by current experimental realizations of strongly interacting Rydberg
gases in lattices. In particular we are interested in the temporal evolution of
quantities such as the density of Rydberg atoms and density-density
correlations when the system is initialized in a fully polarized state without
Rydberg excitations. We show that in the thermodynamic limit the expectation
values of these observables converge at least logarithmically to universal
functions and outline a method to obtain these functions. We prove that a
finite one-dimensional system follows this universal behavior up to a given
time. The length of this universal time period depends on the actual system
size. This shows that already the study of small systems allows to make precise
predictions about the thermodynamic limit provided that the observation time is
sufficiently short. We discuss this for various observables and for systems
with different dimensions, interaction ranges and boundary conditions.Comment: 16 pages, 3 figure
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