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One of the most important properties of very recently reported FeSe based superconductors is the robustness of their superconductivity under applied magnetic field. The synthesis and control of superconductivity in FeSe based compounds is rather a difficult task. Synthesis and physical property characterization for optimized superconductivity of FeSe 1/2 Te 1/2 at 13 K is reported here. The compound crystallized in a tetragonal structure with lattice parameters a = 3.8015͑2͒ and c = 6.0280͑4͒ Å. Magnetization measurements indicated bulk superconductivity with lower critical field ͑H c1 ͒ of around 180 Oe. By applying Ginzburg-Landau theory, the H c2 ͑0͒ value is estimated to be ϳ1840 kOe for the 90% of resistive transition. A heat capacity measurement revealed bulk superconductivity by a hump at T c near 13 K and an expected decrease in the same was observed under an applied magnetic field.

We report the experimental and theoretical study on magnetic nature of Bi 3 Ni system. The structure is found to be orthorhombic (Pnma) with lattice parameters a = 8.879Å b = 4.0998Å and c = 4.099Å. The title compound is synthesized via a solid state reaction route by quartz vacuum encapsulation of 5N purity stoichiometric ingredients of Ni and Bi. The superconducting transition temperature is found to be 4.1 K as confirmed from magnetization and specific heat measurements. The lower critical field (H c1 ) and irreversibility field (H irr ) are around 150 and 3000Oe respectively at 2K. Upper critical field (Hc 2 ) as determined from in field (up to 4 Tesla) ac susceptibility is found to be around 2 Tesla at 2K. The normal state specific heat is fitted using Sommerfeld-Debye equation C(T) = γT + βT 3 +δT 5 and the parameters obtained are γ= 11.08mJ/mol-K 2 , β= 3.73mJ/mol-K 4 and δ= 0.0140mJ/mol-K 6 . The calculated electronic density of states (DOS) at Fermi level N(E F ) and Debye temperature Θ D are 4.697 states/eV per formula unit and 127.7K respectively. We also estimated the value of electron phonon coupling constant (λ) to be 1.23, which when substituted in MacMillan equation gives T c = 4.5K. Density functional (DFT) based calculations for experimentally determined lattice parameters show that Ni in this compound is non-magnetic and ferromagnetic interactions seem to play no role. The Stoner condition I*N(E F ) = 0.136 per Ni atom also indicates that system cannot have any ferromagnetism. The fixed spin moment (FSM) calculations by fixing total magnetic moment on the unit cell also suggested that this system does not exhibit any signatures of ferromagnetism. Further it is concluded that ferromagnetic interactions play no role in superconductivity of Bi 3 Ni. This is in contrast to a recent report [14] related to possibility of coexistence of superconductivity and magnetism in Bi 3 Ni. Our results will surely attract more researchers to work on superconductivity of this and similar Ni containing compounds. determined from Reitveld analysis of the studied Bi 3 Ni is given in Fig. 1(b). Results and DiscussionThe DC and AC magnetic susceptibility plots of studied Bi 3 Ni are shown in Fig. 2 and 3 respectively. Namely, Fig. 2(a) depicts the DC magnetic susceptibility (χ) in both zero-fieldcooled (FC) and field-cooled (FC) situations in temperature range of 2K to 10K. The applied field is 10Oe. Superconductivity is observed at 4.1K with a sharp diamagnetic transition in magnetic susceptibility (χ) in both ZFC and FC situations. The superconducting volume fraction seems to be around 87.6% as calculated from FC (χ). This is slightly higher than as reported in ref.13.Though an estimated value is given, still we believe estimating superconducting volume 4 fraction without exactly knowing the pinning properties is not correct. What one can safely conclude from Fig. 2(a) is that the studied Bi 3 Ni is a bulk superconductor with superconducting transition temperature (T c ) at 4.1K. The AC susceptibility of Bi 3 Ni i...

Since the discovery of topological insulators (TIs), there are considerable interests in demonstrating metallic surface states (SS), their shielded robust nature to the backscattering and study their properties at nanoscale dimensions by fabricating nanodevices. Here we address an important scientific issue related to TI whether one can clearly demonstrate the robustness of topological surface states (TSS) to the presence of disorder that does not break any fundamental symmetry. The simple straightforward method of FIB milling was used to synthesize nanowires of BiSe which we believe is an interesting route to test robustness of TSS and the obtained results are new compared to many of the earlier papers on quantum transport in TI demonstrating the robustness of metallic SS to gallium (Ga) doping. In the presence of perpendicular magnetic field, we have observed the co-existence of Shubnikov-de Haas oscillations and linear magnetoresistance (LMR), which was systematically investigated for different channel lengths, indicating the Dirac dispersive surface states. The transport properties and estimated physical parameters shown here demonstrate the robustness of SS to the fabrication tools triggering flexibility to explore new exotic quantum phenomena at nanodevice level.

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