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We have performed magneto-transport and high-resolution angle-resolved photoelectron spectroscopy (ARPES) measurements on palladium (Pd) doped topological insulator Pd$_{x}$Bi$_{2}$Te$_{3}$ (0 $\leq$ x $\leq$ 0.20) single crystals. We have observed unusually high values of magnetoresistance ($\sim$ 1500%) and mobility ($\sim$ 93000 cm$^{2}$V$^{-1}$s$^{-1}$) at low temperatures for pristine Bi2Te3 that decrease on Pd doping. The Shubnikov-de Haas (SdH) oscillations have been detected for x = 0.05, 0.10, confirming the presence of 2D topological surface states (TSSs) for these samples. The Hall measurement shows the crossover from n-type charge carriers in pristine Bi$_{2}$Te$_{3}$ to p-type charge carriers upon Pd doping. The ARPES measurements show that the conduction band crosses the Fermi level for pristine Bi$_{2}$Te$_{3}$, and the Dirac point of the TSSs and bulk-derived valence bands indicated shift to lower binding energy upon Pd doping in a rigid-band-like way up to x $\sim$0.10. Based on the comparison of the parameters obtained from the SdH and ARPES measurements, the reduction in the kF value in the magneto-transport measurements likely due to the band bending induced by the Schottky barrier., Comment: 18 pages, 16 figures

Half-metallic ferromagnets show 100% spin-polarization at the Fermi level and are ideal candidates for spintronic applications. Despite the extensive research in the field, very few materials have been discovered so far. Here we present results of electronic band structure calculations based on density functional theory and extensive physical-property measurements for Fe3Se4 revealing signatures of half-metallicity. The spin-polarized electronic band structure calculations predict half-metallic ferrimagnetism for Fe3Se4. The electrical resistivity follows exponentially suppressed electron-magnon scattering mechanism in the low-temperature regime and show a magnetoresistance effect that changes the sign from negative to positive with decreasing temperature around 100 K. Other intriguing observations include the anomalous behavior of Hall resistance below 100 K and an anomalous Hall coefficient that roughly follows the \r{ho}2 behavior., Comment: Accepted

The magnetic field driven superconductor to insulator transition in thin films was theoretically analyzed via a vortex-charge duality transformation applied to the Hamiltonian. Vortices condensation was conjectured as the underline physical mechanism of the insulating phase. Experimental evidence supported duality symmetry across the magnetic-field driven superconductor to insulator transition in amorphous Indium Oxide films. Counterintuitively, duality symmetry is broken at low temperatures where the insulating phase develops strongly non linear current-voltage characteristics. Here, we follow the breakdown of duality symmetry down to very low temperatures and demonstrate the restoration of duality symmetry out of equilibrium., Comment: 4 pages, 3 figures

We study the low temperature magneto-transport properties of several highly disordered amorphous Indium oxide(a:InO) samples. Simultaneously fabricated devices comprising a 2-dimensional (2D) film and 10 $\mu$m long wires of different widths were measured to investigate the effect of size as we approach the 1D limit, which is around 4 times the correlation length, and happens to be around 100 nm for a:InO. The film and the wires showed magnetic field ({\it B}) induced superconductor to insulator transition (SIT). In the superconducting side, the resistance increased with decrease in wire width, whereas, an opposite trend is observed in the insulating side. We find that this effect can be explained in light of charge-vortex duality picture of the SIT. Resistance of the 2D film follows an activated behavior over the temperature ($T$), whereas, the wires show a crossover from the high-$T$ activated to a $T$-independent behavior. At high temperature regime the wires' resistance follow the film's until they deviate and became independent of $T$. We find that temperature at which this deviation occurs evolve with magnetic field and the width of the wire, which show the effect of finite size on the transport., Comment: 7 pages, 8 figures, latex/revtex, Accepted in Phys.Rev. B

We study magneto-transport properties of several amorphous Indium oxide nanowires of different widths. The wires show superconducting transition at zero magnetic field, but, there exist a finite resistance at the lowest temperature. The $R(T)$ broadening was explained by available phase slip models. At low field, and far below the superconducting critical temperature, the wires with diameter equal to or less than 100 nm, show negative magnetoresistance (nMR). The magnitude of nMR and the crossover field are found to be dependent on both temperature and the cross-sectional area. We find that this intriguing behavior originates from the interplay between two field dependent contributions., Comment: 11 pages, 7 figures

We present a class of exact solutions of Einstein field equations for a shear-free spherically symmetric anisotropic fluid undergoing radial heat flow. The interior metric fulfilled all the relevant physical and thermodynamic conditions and matched with Vaidya exterior metric over the boundary. Initially the interior solutions represent a static configuration of dissipative fluid which then gradually starts evolving into radiating collapse. The apparent luminosity observed by the distant observer at rest at infinity and the effective surface temperature are zero in remote past at the instance when collapse begins and at the stage when collapsing configuration reach the horizon of the black hole.

We present a detail study of the electrical resistivity, thermoelectric power, magnetic susceptibility \c{hi} and the heat capacity CP in antiferromagnetic layered compounds CuCrS2 and CuCrSe2 at 2K-300K. CuCrS2 showed sharp cusp in \c{hi} and a lambda-like peak in CP at TN = 40K as expected for a 3D- magnetic order, while more metallic CuCrSe2 showed a rounded maximum in \c{hi} and the absence of sharp peak in CP around 55K, the CP at low temperature has T2-dependence in it which suggests the absence of the long range order and 2D spin-liquid like excitation in its magnetic phase. We explain the absence of the magnetic order in the selenide compound as resulting from the effective competition of the magnetic interactions from the distant neighbors; the indirect exchange among the intra-layer Cr-atoms increases in more metallic selenide compound which competes with the direct antiferromagnetic interactions between the Cr-atoms of different layers which destroys the long range magnetic order., Comment: Submitted in JSSC

The electrical, thermal conductivity and Seebeck coefficient of the quenched, annealed and slowly cooled phases of the layer compound CuCrS2 have been reported between 15K to 300K. We also confirm the antiferromagnetic transition at 40K in them by our magnetic measurements between 2K and 300K. The crystal flakes show a minimum around 100K in their in-plane resistance behavior. For the polycrystalline pellets the resistivity depends on their flaky texture and it attains at most 10 to 20 times of the room temperature value at the lowest temperature of measurement. The temperature dependence is complex and no definite activation energy of electronic conduction can be discerned. We find that the Seebeck coefficient is between 200-450 microV/K and is unusually large for the observed resistivity values of between 5-100 mOhm-cm at room temperature. The figure of merit ZT for the thermoelectric application is 2.3 for our quenched phases, which is much larger than 1 for useful materials. The thermal conductivity K is mostly due to lattice conduction and is reduced by the disorder in Cu- occupancy in our quenched phase. A dramatic reduction of electrical and thermal conductivity is found as the antiferromagnetic transition is approached from the paramagnetic region, and K subsequently rises in the ordered phase. We discuss the transport properties as being similar to a doped Kondo-insulator.