Iron pnictide thin films : synthesis and physics

Superconducting thin films play a prominent role in applications of superconductivity and provide an essential source for studying physical phenomena. Here, we summarize the activities for iron pnictide thin films with a focus on the German Special Priority Programme from 2009 until today. The quick availability of such films after the discovery of superconductivity in the iron-based superconductors enabled a number of experiments. After a general introduction and a brief historical overview we focus on film synthesis of iron pnictides by a two-step method and by pulsed laser deposition, the assessment of their application potential, the upper critical fields in iron oxypnictides of F-doped LaOFeAs and F-doped Smmath formulaLamath formulaOFeAs and on superconductivity in Fe/BaFemath formulaAsmath formula heterostructures

Millimeter-wave communication for a last-mile autonomous transport vehicle

Low-speed autonomous transport of passengers and goods is expected to have a strong, positive impact on the reliability and ease of travelling. Various advanced functions of the involved vehicles rely on the wireless exchange of information with other vehicles and the roadside infrastructure, thereby benefitting from the low latency and high throughput characteristics that 5G technology has to offer. This work presents an investigation of 5G millimeter-wave communication links for a low-speed autonomous vehicle, focusing on the effects of the antenna positions on both the received signal quality and the link performance. It is observed that the excess loss for communication with roadside infrastructure in front of the vehicle is nearly half-power beam width independent, and the increase of the root mean square delay spread plays a minor role in the resulting signal quality, as the absolute times are considerably shorter than the typical duration of 5G New Radio symbols. Near certain threshold levels, a reduction of the received power affects the link performance through an increased error vector magnitude of the received signal, and subsequent decrease of the achieved data throughput

Nonmetallic Low-Temperature Normal State of K0.70Fe1.46Se1.85Te0.15

The normal-state in-plane resistivity below the zero-field superconducting transition temperature $T_c$ and the upper critical field Hc2 were measured by suppressing superconductivity in pulsed magnetic fields for K0.70Fe1.46Se1.85Te0.15. The normal-state resistivity $\rho_{ab}$ is found to increase logarithmically with decrasing temperature as $\frac{T}{T_c}\rightarrow 0$. Similar to granular metals, our results suggest that a superconductor - insulator transition below zero-field T$_{c}$ may be induced in high magnetic fields. This is related to the intrinsic real-space phase-separated states common to all inhomogeneous superconductors.Comment: 6 pages, 4 figure

Connectivity analysis for mmWave V2V networks : exploring critical distance and beam misalignment

In this paper, we investigate the analytical connectivity performance of Vehicle-to-Vehicle communications when using millimeter wave carrier frequencies, by taking into account its challenges of high path loss and beam misalignment. The connectivity analysis is carried out in two dimensions; first, an analytical and parametric critical transmission range is developed, based on system parameters such as vehicle density and Signal-to-Interference-Plus-Noise ratio threshold, and second, the beam misalignment probability caused by the in-lane lateral displacement of vehicles is determined. The analysis is carried out for antennas with half power beamwidths of 3◦, 6◦, 10◦, 20◦ and 45◦, resulting in different beamwidth regimes depending upon road curvature and vehicle density. For low/medium vehicle density on low-curvature roads, the sensitivity of the network connectivity to the beamwidth is relatively small. On the other hand, the narrowest beamwidth is the best performer in terms of maximizing connectivity in low/medium vehicle density scenarios on high-curvature roads, and the wider beamwidth is the best performer for high vehicle density on low-curvature roads

Low anisotropic upper critical fields in SmO1-xFxFeAs thin films with a layered hybrid structure

We report on the upper critical fields in SmO 1 - x F x FeAs thin films prepared by pulsed laser deposition. With an F - content gradient along their thickness, the films could be described approximately as layered two - phase hybrid structures comprised of one superconducting layer and one antiferromagnetic layer. An analytical characterization of different thin film samples by AES and STEM - EDX is provided and structural defects, such as antiphase boundaries, were confirmed for films grown at lower deposition temperatures. Electrical transport measurements in pulsed magnetic fields yielded upper critical fields higher than 80 T with an anisotropy y Hc2 ≤ 2.25

Fractional quantum conductance plateaus in mosaic-like conductors and their similarities to the fractional quantum hall effect

A simple route to generate magnetotransport data is reported that results in fractional quantum Hall plateaus in the conductance without invoking strongly correlated physics. Ingredients to the generating model are conducting tiles with integer quantum Hall effect and metallic linkers, further Kirchhoff rules. When connecting few identical tiles in a mosaic, fractional steps occur in the conductance values. Richer spectra representing several fractions occur when the tiles are parametrically varied. Parts of the simulation data are supported with purposefully designed graphene mosaics in high magnetic fields. The findings emphasize that the occurrence of fractional conductance values, in particular in two‐terminal measurements, does not necessarily indicate interaction‐driven physics. The importance of an independent determination of charge densities is underscored and similarities with and differences to the fractional quantum Hall effect are critically discussed

A grid-based coverage analysis of urban mmWave vehicular ad hoc networks

In this letter, a tractable coverage model, specifically designed for urban vehicular ad hoc networks, is presented to aid a better system designer. This is achieved through the use of a model based upon line processes, which simplifies the analysis. It is found, that even in crowded interferer scenarios, mmWave vehicular communications can establish reliable links with an SINR threshold of around 5 dB, with a coverage probability of approximately 0.8 at 50 m separation between a typical transmitter and a typical receiver. These results, and their inference towards the design and deployment of urban vehicular ad-hoc networks, may impact the developments of future vehicle- to-vehicle (V2V) applications and services

Revisiting the Energy-Efficient Hybrid D-A Precoding and Combining Design For mm-Wave Systems

Hybrid digital to analog (D-A) precoding is widely used in millimeter wave systems to reduce the power consumption and implementation complexity incurred by the number of radio frequency (RF) chains that consume a lot of the transmitted power in this system. In this paper, an optimal number of RF chains is proposed to achieve the desired energy efficiency (EE). Here, the optimization problem is formulated in terms of fractional programming maximization, resulting in a method with a twofold novelty: First, the optimal number of RF chains is determined by the proposed bisection algorithm, which results in an optimized number of data streams. Second, the optimal analog precoders/combiners are designed by eigenvalue decomposition and a power iteration algorithm, followed by the digital precoders/combiners which are designed based on the singular value decomposition of the proposed effective uplink and downlink channel gains. Furthermore, the proposed D-A systems are designed carefully to attain a lower complexity than the existing D-A algorithms while achieving reasonable performance. Finally, the impact of utilizing a different number of quantized bits of resolution on the EE is investigated. Simulation results show that the proposed algorithms outperform existing algorithms in terms of EE, spectral efficiency, and computational complexity