A novel ferroelectric Rashba semiconductor

Fast, reversible, and low-power manipulation of the spin texture is crucial for next generation spintronic devices like non-volatile bipolar memories, switchable spin current injectors or spin field effect transistors. Ferroelectric Rashba semiconductors (FERSC) are the ideal class of materials for the realization of such devices. Their ferroelectric character enables an electronic control of the Rashba-type spin texture by means of the reversible and switchable polarization. Yet, only very few materials are established to belong to this class of multifunctional materials. Here, Pb$_{1−x}$Ge$_{x}$Te is unraveled as a novel FERSC system down to nanoscale. The ferroelectric phase transition and concomitant lattice distortion are demonstrated by temperature dependent X-ray diffraction, and their effect on electronic properties are measured by angle-resolved photoemission spectroscopy. In few nanometer-thick epitaxial heterostructures, a large Rashba spin-splitting is exhibiting a wide tuning range as a function of temperature and Ge content. This work defines Pb$_{1−x}$Ge$_{x}$Te as a high-potential FERSC system for spintronic applications

Ferromagnetic MnSb2Te4: A p-type topological insulator with magnetic gap closing at high Curie temperatures of 45-50K

Resumen del trabajo presentado al APS March Meeting, celebrado de forma virtual del 13 al 19 de marzo de 2021Mn enables the formation of intrinsic magnetic topological insulatorsfor the quantum anomalous Hall effect with A1B2C4 stoichiometry, e. g., antiferromagnetic MnBi2Te4 with 25 K Néel temperature. Here, we showthat p-type MnSb2Te4, previously considered topologically trivial, is a ferromagnetic topological insulator with high Curie temperature of 45 to 50 K.It displays out-of-plane magnetic anisotropy, the nontrivial topology is robust in band structure calculations towards magnetic disorder, provides aDirac point of the topological surface state close to the Fermi level with out-of-plane spin polarization in spin-ARPES, and exhibits a magneticallyinduced band gap of 17 meV that closes at the Curie temperature as demonstrated by scanning tunneling spectroscopy. Moreover, it displays acritical exponent of magnetization β≈1, indicating the vicinity of a quantum critical point. We identify the influences of structural and magneticdisorder that render MnSb2Te4 the ideal system for tuning electric and magnetic properties of quantum anomalous Hall systems.Peer reviewe

Nontuberculous mycobacteria in the environment of Hranice Abyss, the world’s deepest flooded cave (Hranice karst, Czech Republic)

Nontuberculous mycobacteria (NTM) are widely distributed in the environment. On one hand, they are opportunistic pathogens for humans and animals, and on the other hand, they are effective in biodegradation of some persistent pollutants. Following the recently recorded large abundance of NTM in extreme geothermal environments, the aim of the study was to ascertain the occurrence of NTM in the extreme environment of the water zone of the Hranice Abyss (HA). The HA mineral water is acidic, with large concentrations of free CO2, and bacterial slimes creating characteristic mucilaginous formations. Both culture and molecular methods were used to compare the mycobacterial diversity across the linked but distinct ecosystems of HA and the adjacent Zbrašov Aragonite Caves (ZAC) with consideration of their pathogenic relevance. Six slowly growing NTM species (M. arupense, M. avium, M. florentinum, M. gordonae, M. intracellulare) and two rapidly growing NTM species (M. mucogenicum, M. sediminis) were identified in the water and in the dry zones at both sites. Proteobacteria were dominant in all the samples from both the HA and the ZAC. The bacterial microbiomes of the HA mineral water and HA slime were similar, but both differed from the microbiome in the ZAC mineral water. Actinobacteria, a phylum containing mycobacteria, was identified in all the samples at low proportional abundance. The majority of the detected NTM species belong among environmental opportunistic pathogens

Enhanced permeability dielectric FeCo/Al2O3 multilayer thin films with tailored properties deposited by magnetron sputtering on silicon

International audienceWe have studied the structural and magnetic properties of enhanced-permeability-dielectric FeCo/Al2O3-multilayer thin films deposited on 8 ''-Si wafers in an industrial magnetron sputtering system. The EPD-multilayers consist of 25 periods of alternating nanometer-thick FeCo-layers deposited by DC sputtering from a Fe60Co40 target and Al2O3-interlayers deposited by RF sputtering from an Al2O3 target. We tuned the magnetic properties of these thin films by varying the thickness of FeCo-layers from 1.1nm to 2.1nm, while the thickness of Al2O3-interlayers remained unchanged (3.5nm). The formation of layers of disconnected FeCo-nanoparticles separated by an Al2O3-matrix was revealed by grazing incidence small angle X-ray-scattering. Further insight into the microstructure of these layers was obtained from X-ray-reflectivity, highly asymmetric-X-ray-diffraction and non-coplanar grazing-incidence-diffraction. The Fe/Co ratio in the FeCo-layers obtained from X-ray-fluorescence measurements was (59 +/- 1)/(41 +/- 1), which is in very good agreement with the nominal value in the Fe60C40 target. Using the standing wave technique we found that most of the Fe and Co atoms were located inside the polycrystalline grains, except for a small fraction that diffused into the Al2O3-matrix, and that the thinner the FeCo-layers thickness the higher the fraction of diffused atoms with respect to those in the grains. Zero-field-cooled, field-cooled, and hysteresis (B-H) and (M-H) measurements showed that the FeCo/Al2O3-multilayers with FeCo-layers thinner than 1.7-1.8 nm exhibit superparamagnetic behavior (no coercivity and remanence) at room temperature with peak relative low-field permeability up to 887. By exceeding this critical thickness, the neighboring FeCo-aggregates started to coalesce, and this led to the ferromagnetic behavior revealed by a finite coercivity and remanence in the hysteresis loops

Triple point fermions in ferroelectric GeTe

Ferroelectric GeTe is unveiled to exhibit an intriguing multiple non-trivial topology of the electronic band structure due to the existence of triple-point and type-II Weyl fermions, which goes well beyond the giant Rashba spin splitting controlled by external fields as previously reported. Using spin- and angle-resolved photoemission spectroscopy combined with ab initio density functional theory, the unique spin texture around the triple point caused by the crossing of one spin degenerate and two spin-split bands along the ferroelectric crystal axis is derived. This consistently reveals spin winding numbers that are coupled with time reversal symmetry and Lorentz invariance, which are found to be equal for both triple-point pairs in the Brillouin zone. The rich manifold of effects opens up promising perspectives for studying non-trivial phenomena and multi-component fermions in condensed matter systems.Comment: 5 pages, 5 figure