36 research outputs found
The interfacial structure of InP(100) in contact with HCl and H2SO4 studied by reflection anisotropy spectroscopy
Indium phosphide and derived compound semiconductors are materials often
involved in high-efficiency solar water splitting due to their versatile
opto-electronic properties. Surface corrosion, however, typically deteriorates
the performance of photoelectrochemical solar cells based on this material
class. It has been reported that (photo)electrochemical surface
functionalisation protects the surface by combining etching and controlled
corrosion. Nevertheless, the overall involved process is not fully understood.
Therefore, access to the electrochemical interface structure under operando
conditions is crucial for a more detailed understanding. One approach for
gaining structural insight is the use of operando reflection anisotropy
spectroscopy. This technique allows the time-resolved investigation of the
interfacial structure while applying potentials in the electrolyte. In this
study, p-doped InP(100) surfaces are cycled between anodic and cathodic
potentials in two different electrolytes, hydrochloric acid and sulphuric acid.
For low, 10 mM electrolyte concentrations, we observe a reversible processes
related to the reduction of a surface oxide phase in the cathodic potential
range which is reformed near open-circuit potentials. Higher concentrations of
0.5 N, however, already lead to initial surface corrosion.Comment: 10 pages, 6 figure
Analyzing the collective emission of a single-photon source based on an ensemble of thermal Rydberg atoms
An ensemble of Rydberg atoms can be excited with lasers such that it evolves
into an entangled state with just one collective excitation within the Rydberg
blockade radius. The decay of this state leads to the emission of a single,
antibunched photon. For a hot vapor of Rubidium atoms in a micro cell we
numerically study the feasibility of such a single-photon source under
different experimental conditions like the atomic density distribution and the
choice of electronic states addressed by the lasers. For the excitation process
with three rectangular lasers pulses, we simulate the coherent dynamics of the
system in a truncated Hilbert space. We investigate the radiative behavior of
the moving Rydberg atoms and optimize the laser pulse sequence accordingly. We
find that the collective decay of the single-excitation leads to a fast and
directed photon emission and further, that a pulse sequence similar to a spin
echo increases the directionality of the photon. Finally, we analyze the
residual double-excitations and find that they do not exhibit these collective
decay properties and play only a minor deleterious role.Comment: 10 pages, 6 figures, 1 table. Removed 6P state calculations for
brevity. Added new results for 5P state calculations. Updated color in
figure
Competing orders and quantum criticality in doped antiferromagnets
We use a number of large-N limits to explore the competition between ground
states of square lattice doped antiferromagnets which break electromagnetic
U(1), time-reversal, or square lattice space group symmetries. Among the states
we find are d-, (s+id)-, and (d+id)-wave superconductors, Wigner crystals,
Wigner crystals of hole pairs, orbital antiferromagnets (or staggered-flux
states), and states with spin-Peierls and bond-centered charge stripe order. In
the vicinity of second-order quantum phase transitions between the states, we
go beyond the large-N limit by identifying the universal quantum field theories
for the critical points, and computing the finite temperature, quantum-critical
damping of fermion spectral functions. We identify candidate critical points
for the recently observed quantum-critical behavior in photoemission
experiments on BSCCO by Valla et al. (Science 285, 2110 (1999)). These involve
onset of a charge density wave, or of broken time-reversal symmetry with (d+id)
or (s+id) pairing, in a d-wave superconductor. It is not required (although it
is allowed) that the stable state in the doped cuprates to be anything other
than the d-wave superconductor--the other states need only be stable nearby in
parameter space. At finite temperatures, fluctuations associated with these
nearby states lead to the observed fermion damping in the vicinity of the nodal
points in the Brillouin zone. The cases with broken time-reversal symmetry are
appealing because the order parameter is not required to satisfy any special
commensurability conditions. The observed absence of inelastic damping of
quasiparticles with momenta (pi,k), (k,pi) (with 0 < k < pi) also appears very
naturally for the case of a transition to (d+id) order.Comment: 26 pages, 13 figures; added references, clarifications, and a new
figur
Digitalisierung und Demokratie
Die Digitalisierung spielt bei den Prozessen und Entwicklungen in einer Demokratie eine immer gröĂere Rolle. Denn Digitalisierung erweitert die Möglichkeiten der Information, Kommunikation und Partizipation. Gleichzeitig können digitale Technologien zu einer schnellen Verbreitung von Falschinformationen beitragen und bergen ein Potenzial fĂŒr Meinungsmanipulation, zum Beispiel vor Wahlen. Dieses Spannungsfeld ist Thema der Stellungnahme "Digitalisierung und Demokratie". Darin analysieren die Autorinnen und Autoren Aspekte des Zusammenspiels von Digitalisierung und Demokratie. Darauf aufbauend formulieren sie Handlungsempfehlungen zur Gestaltung kĂŒnftiger Entwicklungen durch Politik, Recht und Zivilgesellschaft
The EnMAP imaging spectroscopy mission towards operations
EnMAP (Environmental Mapping and Analysis Program) is a high-resolution imaging spectroscopy remote sensing mission that was successfully launched on April 1st, 2022. Equipped with a prism-based dual-spectrometer, EnMAP performs observations in the spectral range between 418.2 nm and 2445.5 nm with 224 bands and a high radiometric and spectral accuracy and stability. EnMAP products, with a ground instantaneous field-of-view of 30 m x 30 m at a swath width of 30 km, allow for the qualitative and quantitative analysis of surface variables from frequently and consistently acquired observations on a global scale. This article presents the EnMAP mission and details the activities and results of the Launch and Early Orbit and Commissioning Phases until November 1st, 2022. The mission capabilities and expected performances for the operational Routine Phase are provided for existing and future EnMAP users
Down-regulation of plant V-type H+-ATPase genes after light-induced inhibition of growth
AbstractCell extension growth in the mesocotyl tip of dark-grown Zea mays L. seedlings is dependent on vacuole enlargement and massive flux of ER and Golgi vesicles. Water flow into the expanding vacuole is driven by ion accumulation, which in turn is energized by the vacuolar H+-ATPase (V-ATPase). The V-ATPase energizes the secondary ion transport into the expanding vacuole. As light exposure leads to a strong inhibition of extension growth, the effect of light on transcript levels for subunits A and c of the V-ATPase was analyzed. Partial homologous cDNAs for subunit A and two isoforms of subunit c were cloned by RT-PCR. In dark-grown seedlings transcript levels for both subunits were much higher in the growing mesocotyl tip than in the fully differentiated mesocotyl tissue. Only in the tip region did light exposure lead to a strong and coordinate down-regulation of both mRNAs whereas in the differentiated mesocotyl only a slight decrease was observed. The results indicate that expression of the âhousekeepingâ V-type H+-ATPase is strongly regulated in response to growth rate