Electronic transport and magnetic properties of ${\mathrm{Ge}}_{1–x}{\mathrm{Mn}}_x∕\mathrm{Ge}\left(100\right)$ films are investigated as a function of Mn dilution. Depending on $x$, characteristic temperatures separate different regimes in both properties. Resistivity exhibits an insulatorlike behavior in the whole temperature range and, below about $80\mathrm{K}$, two distinct activation energies are observed. At a higher temperature value, $T_R$, resistivity experiences a sudden reduction. The Hall coefficient shows a strong contribution from the anomalous Hall effect and, at $T_R$, a sign inversion, from positive to negative, is recorded. The magnetic properties, inferred from magneto-optical Kerr effect, evidence a progressive decrease of the ferromagnetic long range order as the temperature is raised, with a Curie temperature $T_C$ not far from $T_R$. The transport and magnetic results are qualitatively consistent with a percolation mechanism due to bound magnetic polarons in a GeMn diluted magnetic semiconductor, with localized holes [A. Kaminski and S. Das Sarma, Phys. Rev. B 68, 235210 (2003)].

Superconducting and normal state properties of Niobium nanofilms have been systematically investigated as a function of film thickness, on different substrates. The width of the superconducting-to-normal transition for all films is remarkably narrow, confirming their high quality. The superconducting critical current density exhibits a pronounced maximum for thickness around 25 nm, marking the 3D-to-2D crossover. The magnetic penetration depth shows a sizeable enhancement for the thinnest films. Additional amplification effects of the superconducting properties have been obtained with sapphire substrates or squeezing the lateral size of the nanofilms. For thickness close to 20 nm we measured a doubled perpendicular critical magnetic field compared to its large thickness value, indicating shortening of the correlation length and the formation of small Cooper pairs. Our data analysis indicates an exciting interplay between quantum-size and proximity effects together with strong-coupling effects and the importance of disorder in the thinnest films, placing these nanofilms close to the BCS-BEC crossover regime.

The toolbox to study the Universe grew on 14 September 2015 when the LIGO–Virgo collaboration heard a signal from two colliding black holes between 30 and 250 Hz. Since then, many more gravitational waves have been detected as detectors continue to increase sensitivity. However, the current and future interferometric detectors will never be able to detect gravitational waves below a few Hz due to oceanic activity on Earth. An interferometric space mission, the laser interferometer space antenna, will operate between 1 mHz and 0.1 Hz, leaving a gap in the decihertz band. To detect gravitational-wave signals also between 0.1 and 1 Hz, the Lunar Gravitational-wave Antenna will use an array of seismic stations. The seismic array will be deployed in a permanently shadowed crater on the lunar south pole, which provides stable ambient temperatures below 40 K. A cryogenic superconducting inertial sensor is under development that aims for fm/√Hz sensitivity or better down to several hundred mHz, and thermal noise limited below that value. Given the 106 m size of the Moon, strain sensitivities below 10−20 1/√Hz can be achieved. The additional cooling is proposed depending on the used superconductor technology. The inertial sensors in the seismic stations aim to make a differential measurement between the elastic response of the Moon and the inertial sensor proof-mass motion induced by gravitational waves. Here, we describe the current state of research toward the inertial sensor, its applications, and additional auxiliary technologies in the payload of the lunar gravitational-wave detection mission.

We report the observation of a structurally induced doping compensation mechanism in doped semiconductor nanowires that results from the reduced size geometry. This kind of compensation can significantly affect the electronic transport properties of the doped nanowires. We demonstrate that in a crystalline n-type doped Ge wire, compensated by the acceptor-like localized surface states, strong electron-electron interactions occur. Variable range hopping conduction detected in these nanowires is directly generated from strong interactions, exhibiting an unusual large Coulomb gap in the density of states of wires.

Preliminary evidence for the occurrence of high-$T_C$ superconductivity in alkali-doped organic materials, such as potassium-doped p-terphenyl (KPT), were recently obtained by magnetic susceptibility measurements and by the opening of a large superconducting gap as measured by ARPES and STM techniques. In this work, KPT samples have been synthesized by a chemical method and characterized by low-temperature Raman scattering and resistivity measurements. Here, we report the occurrence of a resistivity drop of more than 4 orders of magnitude at low temperatures in KPT samples in the form of compressed powder. This fact was interpreted as a possible sign of a broad superconducting transition taking place below 90 K in granular KPT. The granular nature of the KPT system appears to be also related to the 20 K broadening of the resistivity drop around the critical temperature.