Anisotropic minimal conductivity of graphene bilayers

Fermi line of bilayer graphene at zero energy is transformed into four separated points positioned trigonally at the corner of the hexagonal first Brillouin zone. We show that as a result of this trigonal splitting the minimal conductivity of an undoped bilayer graphene strip becomes anisotropic with respect to the orientation $\theta$ of the connected electrodes and finds a dependence on its length $L$ on the characteristic scale $\ell=\pi/\Delta k\simeq 50 nm$ determined by the inverse of k-space distance of two Dirac points. The minimum conductivity increases from a universal isotropic value $\sigma^{min}_{\bot}=(8/\pi)e^2/h$ for a short strip $L\ll \ell$ to a higher anisotropic value for longer strips, which in the limit of $L\gg \ell$ varies from $(7/3)\sigma^{min}_{\bot}$ at $\theta=0$ to $3\sigma^{min}_{\bot}$ over an angle range $\Delta \theta\sim \ell/L$.Comment: 4 pages, 2 figure

Gate-controlled supercurrent reversal in MoS2_2-based Josephson junctions

Motivated by recent experiments revealing superconductivity in MoS$_2$, we investigate the Josephson effect in the monolayer MoS$_2$ at the presence of an exchange splitting. We show that the supercurrent reversal known as $0-\pi$ transition can occur by varying the doping via gate voltages. This is in contrast to common superconductor/ferromagnet/superconductor junctions in which successive $0-\pi$ transition take place with the variation of junction length or temperature. In fact for the case of MoS$_2$ we find that both the amplitude and the period of oscillations show a dependence on the doping which explains the predicted doping induced supercurrent reversal. These effects comes from the dependence of density and Fermi velocity on the doping strength beside the intrinsic spin splitting in the valence band which originates from spin-orbit interaction.Comment: 5 pages, 3 figure

An updated Checklist of the Marine fishes from Syria with emphasis on alien species

An updated checklist of marine ichthyofauna that are recorded to date, from Syrian marine water including 297 species (belonging to 220 genera, 111 families, 36 orders, and 3 classes) is presented. Sparidae is the dominant family (28 species), followed by Blenniidae (15 species), while 55 families are represented by 1 species. The Chondrichthyes present in Syria were cross-checked for the first time. The status, frequency, the main fishing gear targeting common species, in addition to the fishing method by which the rare species were caught, are also provided. Four species are recorded for the first time herein: Stomias boa boa (Risso, 1810), Hymenocephalus italicus Giglioli, 1884, Scarus ghobban Forsskal, 1775, and Nettastoma melanurum Rafinesque, 1810. In this inventory, 56 Lessepsian migrant species are also included, with 16 of them being considered as very common and of positive economic importance. Alien species have been grouped into three categories namely established (49 species), casual (2 species), and single records (5 species). Twenty-eight species were disregarded from this list, due to lack of solid documentation on their presence

Synthesis of nanostructured titanium carbide from titanium oxide and Ferro-titanium through mechanical activation

Carbides of Ti have been synthesized directly from its oxides and ferroalloys through high energy mechanical milling and heat treatment. Powders of TiO2 and Fe-Ti mixed with various proportions of graphite were milled in a planetary ball mill for 30 to 90 hours. The milled mixtures were then heat treated at 1100-1300oC for 1 to 2 hours. The as-milled and heat treated powders were characterized by SEM-EDAX, XRD, Pycnometer, and BET techniques. Higher graphite content in the mixture apparently impeded the impact action during milling. Even though longer milling time ensured diminishing particle size, as revealed in SEM, agglomeration was noticed. Formation of carbides of Ti was detected by XRD even in as-milled powders milled for various lengths of time with reduced graphite content along with the change in phase from anatase to rutile. Nanostructured titanium carbide was successfully synthesized under suitable processing conditions using various raw materials. Density, specific surface area and average particle size of the as-milled and heat treated mixtures were correlated with milling time and heat treatment temperature

Josephson effect in mesoscopic graphene strips with finite width

We study Josephson effect in a ballistic graphene strip of length $L$ smaller than the superconducting coherence length and arbitrary width $W$. We find that the dependence of the critical supercurrent $I_{c}$ on $W$ is drastically different for different types of the edges. For \textit{smooth} and \textit{armchair} edges at low concentration of the carriers $I_{c}$ decreases monotonically with decreasing $W/L$ and tends to a constant minimum for a narrow strip $W/L\lesssim1$. The minimum supercurrent is zero for smooth edges but has a finite value $e\Delta_{0}/\hbar$ for the armchair edges. At higher concentration of the carriers, in addition to this overall monotonic variation, the critical current undergoes a series of peaks with varying $W$. On the other hand in a strip with \textit{zigzag} edges the supercurrent is half-integer quantized to $(n+1/2)4e\Delta_{0}/\hbar$, showing a step-wise variation with $W$.Comment: 4 pages, 3 figure