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Complex plasma experiments under microgravity conditions in the International Space Station ISS, complementing research on Earth, are very important for the progress in this field. Complex plasmas consist of micrometre-sized highly charged particles ("microparticles") embedded in an ionized gas ("plasma"). The microparticle ensemble resembles a classical system of interacting atoms. This system can form all of the classic phases, i.e., crystalline, liquid and gaseous. It can also support the propagation of sound waves, solitons and shock waves.

In experiments carried out on Earth, gravity pulls the microparticles downwards resulting in two-dimensional structures. Under microgravity conditions it is possible to investigate big, three-dimensional systems. The PK-3 Plus laboratory provides ideal conditions for such experiments. It is installed in the Russian segment of the ISS and has been used repeatedly over the last 6 years.

We performed experiments to measure the speed of sound during two missions with cosmonauts Volkov and Skvortsov. In Figs. (a) and (b) we show how a bigger "probe" particle penetrated a cloud of smaller microparticles. At a speed several times faster than the speed of sound it excited a Mach cone. A double cone structure is discernible in this "atomistic" system. While moving through the cloud, the probe particle is decelerated to subsonic speeds. By measuring the Mach cone angle at several probe particle velocities, we determined the Mach relation. This allows us to directly measure the speed of sound and to infer the microparticle charge. In addition, the experimental results agree well with a 3D molecular-dynamics simulation, demonstrating in particular a double Mach cone structure.

One of the most important challenges in seeking for competitive energy resources is to increase the efficiency of solar cells. The intermediate band solar cell promises highest efficiencies in a single gap device, since it allows for the absorption of below-bandgap photons via a subband located within the host material's bandgap. In order to generate an isolated subband, electronically coupled stacks of quantum dots (QDs) have been proposed. The built-in potential in the intrinsic region of the solar cell however unavoidably lifts the approximate degeneracy between the QD electron eigenenergies. Hence, the wave functions in adjacent layers would be electronically decoupled, resulting in carrier localization.

To avoid this effect and facilitate the formation of a QD-subband, the present work focuses on the integration of tailored quaternary AlGaInAs QDs. it deals with three major goals in quantum dot solar cell research: Increasing QD absorption by the fabrication of high areal density QDs, engineering the QD's bandgap to tailor their absorption range, and preserving the possibility to maintain an intermediate band despite the built-in potential being present in solar cell p-n-junctions. By a suitable choice of QD composition, shape and barrier thickness they show by simulations routes toward QD-IBSC designs, whereas they experimentally demonstrate a widened spectral absorption range.

The article summarised here leads to a better understanding of subatomic particles using a new cold-atom setup. The work make it easier to study atomic or subatomic-scale properties of the building blocks of matter (which also include protons, neutrons and electrons) known as fermions by slowing down the movement of a large quantity of gaseous atoms at ultra-low temperature.

Thanks to the laser cooling method for which Claude Cohen-Tannoudji, Steven Chu and William D. Phillips received the Nobel Prize in 1997, the authors succeeded in creating the largest Lithium 6 (⁶Li) and Potassium 40 (⁴⁰K) gas mixture to date. The experimental approach involved confining gaseous atoms under ultra-high vacuum using electromagnetic forces, in an ultra-freeze trap of sorts.

This trap enabled them to load twice as many atoms than previous attempts at studying such gas mixtures, reaching a total on the order of a few billion atoms under study at a temperature of only a few hundred microKelvins (corresponding to a temperature near the absolute zero of roughly -273 °C).

Given that the results of this study significantly increased the number of gaseous atoms under study, it will facilitate future simulation of subatomic-scale phenomena in gases. In particular, it will enable future experiments in which the gas mixture is brought to a so-called degenerate state characterised by particles of different species with very strong interactions. Following international efforts to produce the conditions to study subatomic-scale properties of matter under the quantum simulation program, this could ultimately help scientists to understand quantum mechanical phenomena occurring in neutron stars and so-called many-body problems such as high-temperature superconductivity.