Mario Novak

Electrical Detection of the Spin Polarization Due to Charge Flow in the Surface State of the Topological Insulator Bi1.5Sb0.5Te1.7Se1.3

We detected the spin polarization due to charge flow in the spin nondegenerate surface state of a three-dimensional topological insulator by means of an all-electrical method. The charge current in the bulk-insulating topological insulator Bi1.5Sb0.5Te1.7Se1.3 (BSTS) was injected/extracted through a ferromagnetic electrode made of Ni80Fe20, and an unusual current-direction-dependent magnetoresistance gave evidence for the appearance of spin polarization, which leads to a spin-dependent resistance at the BSTS/Ni80Fe20 interface. In contrast, our control experiment on Bi2Se3 gave null result. These observations demonstrate the importance of the Fermi-level control for the electrical detection of the spin polarization in topological insulators.

Tunability of thek-space location of the Dirac cones in the topological crystalline insulator Pb1−xSnxTe

We have performed systematic angle-resolved photoemission spectroscopy of the topological crystalline insulator (TCI) Pb1-xSnxTe to elucidate the evolution of its electronic states across the topological phase transition. As previously reported, the band structure of SnTe (x = 1.0) measured on the (001) surface possesses a pair of Dirac-cone surface states located symmetrically across the Xbar point in the (110) mirror plane. Upon approaching the topological phase transition into the trivial phase at x_c ~ 0.25, we discovered that Dirac cones gradually move toward the Xbar point with its spectral weight gradually reduced with decreasing x. In samples with x <= 0.2, the Dirac-cone surface state is completely gone, confirming the occurrence of the topological phase transition. Also, the evolution of the valence band feature is found to be consistent with the bulk band inversion taking place at x_c. The tunability of the location of the Dirac cones in the Brillouin zone would be useful for applications requiring Fermi-surface matching with other materials, such as spin injection.

Large linear magnetoresistance in the Dirac semimetal TlBiSSe

The mixed-chalcogenide compound TlBiSSe realizes a three-dimensional (3D) Dirac semimetal state. In clean, low-carrier-density single crystals of this material, we found Shubnikov--de Haas oscillations to signify its 3D Dirac nature. Moreover, we observed very large linear magnetoresistance (MR) approaching 10 000% in 14 T at 1.8 K, which diminishes rapidly above 30 K. Our analysis of the magnetotransport data points to the possibility that the linear MR is fundamentally governed by the Hall field; although such a situation has been predicted for highly inhomogeneous systems, inhomogeneity does not seem to play an important role in TlBiSSe. Hence, the mechanism of large linear MR is an intriguing open question in a clean 3D Dirac system.

Unusual nature of fully gapped superconductivity in In-doped SnTe

The superconductor Sn_{1-x}In_{x}Te is a doped topological crystalline insulator and has become important as a candidate topological superconductor, but its superconducting phase diagram is poorly understood. By measuring about 50 samples of high-quality, vapor-grown single crystals, we found that the dependence of the superconducting transition temperature Tc on the In content x presents a qualitative change across the critical doping xc ~ 3.8%, at which a structural phase transition takes place. Intriguingly, in the ferroelectric rhombohedral phase below the critical doping, Tc is found to be strongly ENHANCED with impurity scattering. It appears that the nature of electron pairing changes across xc in Sn_{1-x}In_{x}Te.

Two types of Dirac-cone surface states on the (111) surface of the topological crystalline insulator SnTe

We have performed angle-resolved photoemission spectroscopy (ARPES) on the (111) surface of the topological crystalline insulator SnTe. Distinct from a pair of Dirac-cone surface states across the X_bar point of the surface Brillouin zone on the (001) surface, we revealed two types of Dirac-cone surface states each centered at the G_bar and M_bar points, which originate from the bulk-band inversion at the L points. We also found that the energy location of the Dirac point and the Dirac velocity are different from each other. This ARPES experiment demonstrates the surface states on different crystal faces of a topological material, and it elucidates how mirror-symmetry-protected Dirac cones of a topological crystalline insulator show up on surfaces with different symmetries.

Mathematical Modelling as a Tool for Optimized PHA Production

The potential of poly(hydroxyalkanoates) (PHAs) to replace conventional plastic materials justifies the increasing attention they have drawn both at lab-scale and in industrial biotechnology. The improvement of large-scale productivity and biochemical/genetic properties of producing strains requires mathematical modeling and process/strain optimization procedures. Current models dealing with structurally diversified PHAs, both structured and unstructured, can be divided into formal kinetic, low-structured, dynamic, metabolic (high-structured), cybernetic, neural networks and hybrid models; these attempts are summarized in this review. Characteristic properties of specific groups of models are stressed in light of their benefit to the better understanding of PHA biosynthesis, and their applicability for enhanced productivity. Unfortunately, there is no single type of mathematical model that expresses exactly all the characteristics of producing strains and/or features of industrial-scale plants; in addition, the different requirements for modelling of PHA production by pure cultures or mixed microbial consortia have to be addressed. Therefore, it is crucial to sophisticatedly adapt and fine-tune the modelling approach accordingly to actual processes, as the case arises. For “standard microbial cultivations and everyday practices”, formal kinetic models (for simple cases) and “low-structured” models will be appropriate and of great benefit. They are relatively simple and of low computational demand. To overcome the specific weaknesses of different established model types, some authors use hybrid models. Here, satisfying compromises can be achieved by combining mechanistic, cybernetic, and neural and computational fluid dynamics (CFD) models. Therefore, this hybrid modelling approach appears to constitute the most promising solution to generate a holistic picture of the entire PHA production process, encompassing all the benefits of the original modelling strategies. Complex growth media require a higher degree of model structuring. For scientific purposes and advanced development of industrial equipment in the future, real systems will be modelled by highly organized hybrid models. All solutions related to modelling PHA production are discussed in this review.

The VLA-COSMOS 3 GHz Large Project: The infrared-radio correlation of star-forming galaxies and AGN to z ≲ 6

We examine the behaviour of the infrared-radio correlation (IRRC) over the range 0 <z ≲ 6 using new, highly sensitive 3 GHz observations with the Karl G. Jansky Very Large Array (VLA) and infrared data from the Herschel Space Observatory in the 2 deg^2 COSMOS field. We distinguish between objects where emission is believed to arise solely from star-formation, and those where an active galactic nucleus (AGN) is thought to be present. We account for non-detections in the radio or in the infrared using a doubly-censored survival analysis. We find that the IRRC of star-forming galaxies, quantified by the infrared-to-1.4 GHz radio luminosity ratio (q_(TIR)), decreases with increasing redshift: q_(TIR)(z) = (2.88 ± 0.03)(1 + z)^(−0.19 ± 0.01). This is consistent with several previous results from the literature. Moderate-to-high radiative luminosity AGN do not follow the same q_(TIR)(z) trend as star-forming galaxies, having a lower normalisation and steeper decrease with redshift. We cannot rule out the possibility that unidentified AGN contributions only to the radio regime may be steepening the observed q_(TIR)(z) trend of the star-forming galaxy population. We demonstrate that the choice of the average radio spectral index directly affects the normalisation, as well as the derived trend with redshift of the IRRC. An increasing fractional contribution to the observed 3 GHz flux by free-free emission of star-forming galaxies may also affect the derived evolution. However, we find that the standard (M82-based) assumption of the typical radio spectral energy distribution (SED) for star-forming galaxies is inconsistent with our results. This suggests a more complex shape of the typical radio SED for star-forming galaxies, and that imperfect K corrections in the radio may govern the derived trend of decreasing q_(TIR) with increasing redshift. A more detailed understanding of the radio spectrum is therefore required for robust K corrections in the radio and to fully understand the cosmic evolution of the IRRC. Lastly, we present a redshift-dependent relation between rest-frame 1.4 GHz radio luminosity and star formation rate taking the derived redshift trend into account.

Footprint area analysis of binary imaged Cupriavidus necator cells to study PHB production at balanced, transient, and limited growth conditions in a cascade process

Statistical distribution of cell and poly[3-(R)-hydroxybutyrate] (PHB) granule size and number of granules per cell are investigated for PHB production in a five-stage cascade (5CSTR). Electron microscopic pictures of cells from individual cascade stages (R1–R5) were converted to binary pictures to visualize footprint areas for polyhydroxyalkanoate (PHA) and non-PHA biomass. Results for each stage were correlated to the corresponding experimentally determined kinetics (specific growth rate μ and specific productivity π). Log-normal distribution describes PHA granule size dissimilarity, whereas for R1 and R4, gamma distribution best reflects the situation. R1, devoted to balanced biomass synthesis, predominately contains cells with rather small granules, whereas with increasing residence time τ, maximum and average granule sizes by trend increase, approaching an upper limit determined by the cell’s geometry. Generally, an increase of intracellular PHA content and ratio of granule to cell area slow down along the cascade. Further, the number of granules per cell decreases with increasing τ. Data for μ and π obtained by binary picture analysis correlate well with the experimental results. The work describes long-term continuous PHA production under balanced, transient, and nutrient-deficient conditions, as well as their reflection on the granules size, granule number, and cell structure on the microscopic level.

The clustering and bias of radio-selected AGN and star-forming galaxies in the COSMOS field

Dark matter haloes in which galaxies reside are likely to have a significant impact on their evolution. We investigate the link between dark matter haloes and their constituent galaxies by measuring the angular two-point correlation function of radio sources, using recently released 3 GHz imaging over

Spin-singlet superconductivity in the doped topological crystalline insulator Sn0.96In0.04Te

\sim 2 \ \mathrm{deg}^2