Search

Both preserved gapless states and gapping of Dirac states due to broken time reversal symmetry in bismuth chalcogenide topological insulators with surface and bulk magnetic impurities have been observed and reported in the literature. In order to shed more light on the mechanism of such effects we have performed comprehensive element selective study of the impact of Fe impurity position in the Bi2Se3 lattice on its magnetism. The iron atoms were imbedded in the structure (volume dopants) or deposited on the surface (adatoms) and they revealed striking phenomena. Volume doping preserves non-trivial topology of Bi1.98Fe0.02Se3. Fe atoms not only substitute Bi, but also locate in van der Waals gap. The former are magnetically isotropic, while the latter reveal large magnetic moment (4.5 μB) with perpendicular anisotropy if located near the surface. Majority of Fe adatoms on the surface of Bi2Se3 exhibit weaker moment (3.5 μB) with in-plane anisotropy, as expected for non-interacting species. Negligible interaction between surface electronic states and magnetic adatoms is confirmed by identical vibration spectra of Fe deposited on TI surface of Bi2Se3 and non-TI surface of Bi2S3. The data gathered show how indispensable is the knowledge of the magnetic impurity distribution for applications of bismuth chalcogenide systems. [ABSTRACT FROM AUTHOR]

The effects of habitat fragmentation and the resulting decreases in effective population sizes are not easy to document because they take place over many generations and may be affected by factors other than demographic ones. Here, we used 22 microsatellite loci to investigate genetic structure and diversity in populations of edible dormice Glis glis from habitats that varied widely in area and in the degree of connectivity to other populations. We found that populations from the most fragmented north-western region of Poland were characterized by extremely limited gene flow and low genetic diversity compared to less fragmented populations from southern Poland. STRUCTURE analysis revealed three genetic groups in Poland, which might reflect adaptation to environmental conditions across south-north and east-west gradients, but could also be due to historical patterns of post-glacial colonization. The latter hypothesis is suggested by the observation that southern populations from Poland grouped with those from the Balkans based on microsatellite data; however, the fact that all Polish populations shared western mt DNA cytochrome b haplotypes is inconsistent with this scenario. We discuss the consequences of our findings for the conservation of the edible dormouse in Poland. [ABSTRACT FROM AUTHOR]

Both preserved gapless states and gapping of Dirac states due to broken time reversal symmetry in bismuth chalcogenide topological insulators with surface and bulk magnetic impurities have been observed and reported in the literature. In order to shed more light on the mechanism of such effects we have performed comprehensive element selective study of the impact of Fe impurity position in the Bi2Se3 lattice on its magnetism. The iron atoms were imbedded in the structure (volume dopants) or deposited on the surface (adatoms) and they revealed striking phenomena. Volume doping preserves non-trivial topology of Bi1.98Fe0.02Se3. Fe atoms not only substitute Bi, but also locate in van der Waals gap. The former are magnetically isotropic, while the latter reveal large magnetic moment (4.5 μB) with perpendicular anisotropy if located near the surface. Majority of Fe adatoms on the surface of Bi2Se3 exhibit weaker moment (3.5 μB) with in-plane anisotropy, as expected for non-interacting species. Negligible interaction between surface electronic states and magnetic adatoms is confirmed by identical vibration spectra of Fe deposited on TI surface of Bi2Se3 and non-TI surface of Bi2S3. The data gathered show how indispensable is the knowledge of the magnetic impurity distribution for applications of bismuth chalcogenide systems. [ABSTRACT FROM AUTHOR]

We present STM/STS, ARPES and magnetotransport studies of the surface topography and electronic structure of pristine Bi 2 Se 3 in comparison to Bi 1.96 Mg 0.04 Se 3 and Bi 1.98 Fe 0.02 Se 3 . The topography images reveal a large number of complex, triangle-shaped defects at the surface. The local electronic structure of both the defected and non-defected regions is examined by STS. The defect-related states shift together with the Dirac point observed in the undefected area, suggesting that the local electronic structure at the defects is influenced by doping in the same way as the electronic structure of the undefected surface. Additional information about the electronic structure of the samples is provided by ARPES, which reveals the dependence of the bulk and surface electronic bands on doping, including such parameters as the Fermi wave vector. The subtle changes of the surface electronic structure by doping are verified with magneto-transport measurements at low temperatures (200 mK) allowing the detection of Shubnikov-de Haas (SdH) quantum oscillations.

Single-phase multicomponent perovskite-type cobalt oxide containing five cations in equiatomic amounts on the A-site, namely, (Gd 0.2 Nd 0.2 La 0.2 Sm 0.2 Y 0.2 )CoO 3 , has been synthesized via the modified coprecipitation hydrothermal method. Using an original approach for heat treatment, which comprises quenching utilizing liquid nitrogen as a cooling medium, a single-phase ceramic with high configuration entropy, crystallizing in an orthorhombic distorted structure was obtained. It reveals the anomalous temperature dependence of the lattice expansion with two weak transitions at approx. 80 and 240 K that are assigned to gradual crossover from the low- via intermediate- to high-spin state of Co 3+ . The compound exhibits weak ferromagnetism at T ≤ 10 K and signatures of antiferromagnetic correlations in the paramagnetic phase. Ab initio calculations predict a band gap Δ = 1.18 eV in the ground-state electronic structure with the dominant contribution of O_p and Co_d orbitals in the valence and conduction bands, respectively. Electronic transport measurements confirm the negative temperature coefficient of resistivity characteristic to a semiconducting material and reveal a sudden drop in activation energy at T ∼ 240 K from E a ∼ 1 eV in the low-temperature phase to E a ∼ 0.3 eV at room temperature. The possibility of fine tuning of the semiconducting band gap via a subtle change in A-site stoichiometry is discussed., Competing Interests: The authors declare no competing financial interest.

Warmer winters may lead to changes in the hibernation behaviour of bats, such as the barbastelle Barbastella barbastellus, which prefers to hibernate at low temperatures. The species is also known for its large annual fluctuations in the number of wintering individuals, so inference about population trends should be based on long-term data. Prior to 2005, analyses indicated stable or even increasing barbastelle population in Poland. We analysed the results of 13 winter bat counts (2005-2017) of the species from 15 of the largest hibernacula, and additional site of 47 small bunkers, in Poland. The total number of wintering individuals remained stable during the study period, because the barbastelle is not a long-distance migrant, this likely reflects the national population trend. On the basis of mean winter air temperatures we divided the country into four thermal regions. Analyses of barbastelle abundance in hibernacula in the four regions revealed a 4.8% annual mean increase in numbers in the coldest region, where mean winter temperatures were below -2°C, annual mean declines of 3.3% and 3.1% in two warmer regions of western Poland, but no trend in the region of intermediate mean winter temperatures of between -1°C and -2°C. Overall, there was a significant, but weak, negative correlation between the abundance of hibernating individuals and the mean winter temperature. On the other hand, the number of individuals hibernating in small bunkers increased, even though the site was located in one of the warm regions. The results indicate a warming climate will likely reduce the use of large, well-insulated winter roosts by species that prefer colder conditions-and that this is already happening. For forest-dwelling bats, such as the barbastelle, for which monitoring schemes are primarily based on winter surveys of large hibernacula, estimations of population trends may consequently become less reliable., Competing Interests: he authors have declared that no competing interests exist.