The transport and magnetic studies are performed on high quality FeTe 0.60 Se 0.40 single crystals to determine the upper critical field (H c2 ), lower critical field (H c1 ) and the critical current density (J c ). The value of the upper critical field H c2 is very large, whereas the activation energy determined from the slope of the Arrhenius plots is found to be lower than that in the FeAs122 superconductors. The lower critical field is determined in 'ab' direction and 'c' direction of the crystal, and found to have anisotropy (= H c1//c / H c1//ab ) ~ 4. The magnetic isotherms measured up to 12 Tesla shows the presence of fishtail behavior. The critical current density at 1.8K of the single crystal is found to be almost same in both 'ab' and 'c' directions in the low field regime. 74.25.Ha, 74.25.Op, 74.25.Sv

We present a study of the Seebeck and Nernst coefficients of Fe1+yTe1−xSex extended up to 28 T. The large magnitude of the Seebeck coefficient in the optimally doped sample tracks a remarkably low normalized Fermi temperature, which like other correlated superconductors, is only one order of magnitude larger than Tc. We combine our data with other experimentally measured coefficients of the system to extract a set of self-consistent parameters, which identify Fe1+yTe0.6Se0.4 as a low-density correlated superconductor barely in the clean limit. The system is subject to strong superconducting fluctuations with a sizeable vortex Nernst signal in a wide temperature window.

The results of low temperature thermoelectric power and the specific heat of 1T-VSe 2 (Vanadium diselenide) have been reported along with the electrical resistivity, and Hall coefficient of the compound. The Charge Density Wave (CDW) transition is observed near 110K temperature in all these properties. The Thermoelectric power has been measured from 15K to 300K spanning the incommensurate and commensurate CDW regions. We observed a weak anomaly at the CDW transition for the first time in the specific heat of VSe 2 . The linear temperature dependence of resistivity and thermoelectric power at higher temperatures suggests a normal metallic behavior and electron-phonon scattering above the CDW transition. The positive thermoelectric power and negative Hall coefficient along with strongly temperature dependent behavior in the CDW phase suggest a mixed conduction related to the strongly hybridized s-p-d bands in this compound.

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Thermoelectric properties of polycrystalline p-type ZrTe5 are reported in temperature (T) range 2 -340 K. Thermoelectric power (S) is positive and reaches up to 458 V/K at 340 K on increasing T. The value of Fermi energy 16 meV, suggests low carrier density of  9.5  10 18 cm -3 . A sharp anomaly in S data is observed at 38 K, which seems intrinsic to p-type ZrTe5. The thermal conductivity () value is low (2 W/m-K at T = 300 K) with major contribution from lattice part. Electrical resistivity data shows metal to semiconductor transition at T ~ 150 K and non-Arrhenius behavior in the semiconducting region. The figure of merit zT (0.026 at T = 300 K) is ~ 63% higher than HfTe5 (0.016), and better than the conventional SnTe, p-type PbTe and bipolar pristine ZrTe5 compounds.

We report the occurrence of superconductivity in polycrystalline samples of ZrTe3 at 5.2 K temperature at ambient pressure. The superconducting state coexists with the charge density wave (CDW) phase, which sets in at 63K. The intercalation of Cu or Ag, does not have any bearing on the superconducting transition temperature but suppresses the CDW state. The feature of CDW anomaly in these compounds is clearly seen in the DC magnetization data. Resistivity data is analysed to estimate the relative loss of carriers and reduction in the nested Fermi surface area upon CDW formation in the ZrTe 3 and the intercalated compounds.

We report the evolution of structural, magnetic and dielectric properties due to partial substitution of Ba by Sr in the high temperature multiferroic YBaCuFeO 5 . This compound exhibits ferroelectric and antiferromagnetic transitions around 200 K and these two phenomena are presumed to be coupled with each other. Our studies on magnetic and dielectric properties of the YBa 1-x Sr x CuFeO 5 (x = 0.0, 0.25 and 0.5) show that substitution of Sr shifts magnetic transition towards higher temperature whereas dielectric transition to lower temperature. These results points to the fact that magnetic and dielectric transitions get decoupled as a result of chemical pressure in form of Sr substitution. The nature of magnetodielectric coupling changes across the series with the presence of higher order coupling terms. Additionally in these compounds glassy dynamics of electric dipoles is observed at low temperatures.

We report a comparative study of the series Fe1.1Te1−xSex and the stoichiometric FeTe1−xSex to bring out the difference in their magnetic, superconducting and electronic properties. The Fe1.1Te1−xSex series is found to be magnetic and its microscopic properties are elucidated through Mössbauer spectroscopy. The magnetic phase diagram of Fe1.1Te1−xSex is traced out and it shows the emergence of spin-glass state when the antiferromagnetic state is destabilized by the Se substitution. The isomer shift and quadrupolar splitting obtained from the Mössbauer spectroscopy clearly brings out the electronic differences in these two series.