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We report large magnetoresistance (MR) and Shubnikov-de Haas (SdH) oscillations in single crystals of magnetically (M= Ni and Fe) doped ${\mathrm{M}}_{x}{\mathrm{Bi}}_{0.97\ensuremath{-}x}{\mathrm{Sb}}_{0.03}$ $(x=0, 0.02)$ topological insulators. The $R\overline{3}m$ symmetry and phase have been confirmed by the Rietveld refinement of x-ray diffraction data. Interestingly, a magnetic field induced phase transition from semimetallic to semiconducting type is found with the energy gap around 80 meV at 15 T in the $x=0$ sample. Moreover, we observe linear behavior of MR up to 15 T in transverse mode and SdH oscillations in longitudinal mode where the field direction is parallel with respect to the current and crystal plane. For the parent sample, we found the coherence length ${L}_{\ensuremath{\phi}}=12.7\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$ through the fitting of MR data in transverse mode with modified H-L-N equation. The extracted frequencies of SdH oscillations using the fast Fourier transform method and Landau level (LL) fan diagram are found to be consistent for the parent and Ni doped samples. The determined Fermi surface area is found to be slightly larger in Ni doped as compared to the parent sample possibly due to change in the Fermi energy. The Kohler's plots indicate a single scattering mechanism below 100 K. More importantly, the analysis with the help of the LL fan diagram reveals the nonzero Berry phase ${\ensuremath{\phi}}_{\mathrm{B}}=\ensuremath{-}(1\ifmmode\pm\else\textpm\fi{}0.1)\ensuremath{\pi}$, which demonstrates the nontrivial topological states near the Dirac point in the parent and Ni doped samples.

We report on the synthesis, and structural – magnetic characterizations of Mn doped Bi2Se3 towards achieving a magnetically doped topological insulator. High quality single crystals of MnxBi2−xSe3 (x = 0, 0.03, 0.05, 0.1) are grown and analysed by X-ray diffraction (XRD), Low Energy Electron Diffraction (LEED), Scanning electron microscopy (SEM), and X-ray absorption near-edge structure spectroscopy (XANES). Magnetic properties of these samples under ZFC-FC protocol and isothermal magnetization confirm ferromagnetic correlation above x = 0.03 value. XANES measurements confirm that the dopant Mn is in Mn2+ state. This is further reconfirmed to be in high spin state by fitting magnetic data with Brillouin function for J = 5/2. Both Hall and Seebeck measurements indicate a sign change of charge carriers above x = 0.03 value of Mn doping. We propose Mn doped Bi2Se3 to be a potential candidate for electromagnetic and thermoelectric device applications involving topological surface states.

Synthesis and extensive structural, pyroelectric, magnetic, dielectric and magneto-electric characterizations are reported for polycrystalline Co4Nb2O9 towards unraveling the multiferroic ground state. Magnetic measurements confirm that Co4Nb2O9 becomes an anti-ferromagnet at around 28 K. Associated with the magnetic phase transition, a sharp peak in pyroelectric current indicates the appearance of strong magneto-electric coupling below Neel temperature (TN) along with large coupling constant upto 17.8 μC/m2T. Using temperature oscillation technique, we establish Co4Nb2O9 to be a genuine multiferroic with spontaneous electric polarization in the anti-ferromagnetic state in the absence of magnetic field poling. This is in agreement with our low temperature neutron diffraction studies that show the magnetic structure of Co4Nb2O9 to be that of a non-collinear anti-ferromagnet with ferroelectric ground state.

Incorporation of magnetism in graphene based compounds holds great promise for potential spintronic applications. By optimizing point defects and high edge density of defects, we report many-fold increase in the ferromagnetic saturation moment in lacey/holey reduced graphene oxide nanoribbons (LRGONR) as compared to other graphene derivatives. The samples were synthesized using chemical unzipping methodology. Detailed structural and morphological characterizations are discussed that include XRD, Raman, SEM, HRTEM and XPS measurements. Brilluoin function analysis to magnetization data reflects best fit for J = 7/2 with a saturation moment of 1.1 emu/g. The microscopic origin of magnetization in LRGONR is assigned to high edge defect density which has also been correlated to microstructure. Keywords: Holey graphene nanoribbons, Ferromagnetism, High edge density, Point defects

In this paper we present the single crystal growth of Fe0.95Se0.6Te0.4 high TC superconducting sample by the modified Bridgman technique. The x-ray diffraction pattern shows the single crystal nature of the sample, as only (00l) peaks are detectable. The stoichiometric composition has been verified by energy dispersive x-ray analysis. The superconducting transition temperature at 14 K was confirmed through DC magnetization (ZFC-FC) and resistivity measurements. By analyzing the isothermal M-H curves, we determined the value of H_c1 (0) ~360 Oe by extrapolating the data. The temperature coefficient of resistivity obtained using the power law fitting was found to be 0.6. The obtained Raman spectra at room temperature can be interpreted with the tetragonal crystal structure and space group P4/nmm., Comment: conference paper

The surface states of topological insulators (TI) are protected by time reversal symmetry and they display intrinsic spin helicity where the momentum of the charge carriers decides their spin states. As a consequence, a current injected through the surface states becomes spin polarized and this transport spin-polarization leads to a proportionate suppression of Andreev reflection in superconductor/TI junctions. Here we show that upon doping Bi2Se3 with Mn, the transport spin-polarization is seen to be monotonically suppressed. The parent compound Bi2Se3 is found to exhibit a transport spin-polarization of about 63% whereas crystals with 10% Mn doping show transport spin-polarization of about 48%. This suppression is accompanied by an increasing ferromagnetic order of the crystals with Mn doping. Scanning tunneling spectroscopy shows that the topological protection of the surface states reduce due to Mn doping. The net measured transport spin-polarization is due to a competition of this effect with the increased magnetization on Mn doping. The present results provide important insights for the choice of magnetic topological insulators for spintronic applications., Comment: Accepted in Journal of Physics: Condensed Matter, 5 PAGES, 5 FIGURES

We are reporting decrease in superconducting transition temperature accompanied by increased metallicity in indium doped SnTe superconductor. SnTe is a topological crystalline insulator and superconductivity is achieved by indium substitution in place of tin. With application of hydrostatic pressure we find negative dTc/dP of ~ -0.6K/GPa upto 2.5 GPa. The overall phenomenon is ascribed to unconventional superconductivity. Decrease in resistivity is also seen in single crystal SnTe with application of pressure but no evidence of superconductivity is observed.

Recently superconductivity wasreported by Sr intercalation in topological insulator Bi2Se3. In this report we extensively study anisotropic superconductingproperties of Sr0.1Bi2Se3 with transition at ~2.9 through resistivity and DC magnetization measurement. We also discuss synthesis methodology for growth of single crystal Sr-Bi2Se3. The anisotropic properties of Sr0.1Bi2Se3 single crystals were studied using transport measurements. Using Ginzburg Landau formulas the upper critical field Hc2(0) comes out to be 2.1 T and 1.4 T for magnetic field applied along the ab-plane and c-axis of the single crystalsand corresponding Ginzburg - Landau coherence lengths are ξab = 15.3 nm and ξc = 10.2 nm. The sample shows weak electronic anisotropy Γ = 1.5. Hall resistivity is linear with field at 10 K.

We report synthesis of non-centrosymmetric BiPd single crystal by self flux method. The BiPd single crystal is crystallized in monoclinic structure with the P21 space group. Detailed SEM (Scanning Electron Microscopy) results show that the crystals are formed in slab like morphology with homogenous distribution of Bi and Pd. The magnetic susceptibility measurement confirmed that the BiPd compound is superconducting below 4K. Further, BiPd exhibits weak ferromagnetism near the superconducting transition temperature in isothermal magnetization (MH) measurements. The temperature dependent electrical resistivity also confirmed that the BiPd single crystal is superconducting at Tc=4K. Magneto transport measurements showed that the estimated Hc2(0) value is around 7.0kOe. We also obtained a sharp peak in heat capacity Cp(T) measurements at below 4K due to superconducting ordering. The normalized specific-heat jump, DC/{\gamma}Tc, is 1.52, suggesting the BiPd to be an intermediate BCS coupled superconductor. The pressure dependent electrical resistivity shows the Tc decreases with increasing applied pressure and the obtained dTc/dP is -0.62K/Gpa., Comment: 11 pages Text+Figs

Strontium intercalation between van der Waals bonded layers of the topological insulator ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ is found to induce superconductivity with a maximum ${T}_{c}$ of 2.9 K. Transport measurement on a single crystal of the optimally doped sample ${\mathrm{Sr}}_{0.1}{\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ shows weak anisotropy $(\mathrm{\ensuremath{\Gamma}}\ensuremath{\sim}1.5)$ and an upper critical field ${H}_{c2}(0)$ equal to 2.1 T for a magnetic field applied perpendicular to the $c$ axis of the sample. The Ginzburg-Landau coherence lengths are found to be ${\ensuremath{\xi}}_{ab}=15.3$ nm and ${\ensuremath{\xi}}_{c}=10.2$ nm. The lower critical field ${H}_{c1,ab}(0)$ and zero temperature penetration depth ${\ensuremath{\lambda}}_{ab}(0)$ are estimated to be $0.39\ifmmode\pm\else\textpm\fi{}0.02$ mT and $1221\ifmmode\pm\else\textpm\fi{}36$ nm, respectively. Hall and Seebeck measurements confirm the dominance of electronic conduction, and the carrier concentration is surprisingly low $(n=1.85\ifmmode\times\else\texttimes\fi{}{10}^{19}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3})$ at 10 K, indicating the possibility of unconventional superconductivity.

We report on the impact of hydrostatic pressure on the superconductivity of optimally (indium)-doped SnTe which is established to be derived from a topological crystalline insulating phase. Single crystals of Sn1-x In-x Te were synthesized by a modified Bridgman method that exhibited maximum superconducting T-c of 4.4 K for x = 0.5. Hydrostatic pressure up to 2.5 GPa was applied on the crystals of Sn0.5In0.5Te, and electrical resistivity as a function of temperature and pressure was measured. We observed a decrease in the onset superconducting transition temperature from 4.4 K to 2.8 K on increasing pressure from ambient to 2.5 GPa. The normal state resistivity also decreased abruptly by an order of magnitude at 0.5 GPa but for higher pressures, it decreased marginally. From onset, offset and zero resistivity values, dT(c)/dP of similar to -0.6 K GPa(-1) was confirmed. The low temperature normal state resistivity followed T-2 dependence suggesting Fermi liquid behaviour both for ambient and high pressure data. This increase in metallic characteristics accompanied by normal state Fermi liquid behaviour is in accordance with a 'dome structure' for T-c variation with varying carrier concentration.

Bi2Se3 is a well-known Topological Insulator made of quintuple layers of Bi-Se-Bi-Se-Bi stacked with the Van-der-Waals forces which makes it a good accepter of doping at two places; Bi sites and interlayer gaps. In this paper we report the synthesis and characterization of single crystals of Mn doped Bi2Se3. SEM analysis confirms layered structure. Resistivity and Hall measurements have been done to determine charge carrier density and Hall coefficient. Susceptibility data is well fitted to the Curie-Weiss law within the transition range (5K to 125 K). A negative value of ΘP is indicative of weak anti-ferromagnetic correlation with low Mn doping.

SrxBi2Se3 is recently reported to be a superconductor derived from topological insulator Bi2Se3. It shows a maximum resistive Tc of 3.25 K at ambient pressure. We report magnetic (upto 1 GPa) and transport properties (upro 8 Gpa) under pressure for single crystalline Sr0.1Bi2Se3 superconductor. Magnetic measurements show that Tc decreases from ~2.6 K (0 GPa) to ~1.9 K (0.81 GPa). Similar behavior is observed in transport properties as well without much change in the metallic characteristics in normal state resistivity. No reentrant superconducting phase (Physical Review B 93, 144514 (2016)) is observed at high pressure. Normal state resistivity near Tc is explained by Fermi liquid model. Above 100 K, a polaronic hopping conduction mechanism with two parallel channels for current flow is indicated. Band structure calculations indicate decreasing density of states at Fermi level with pressure. In consonance with transition temperature suppression in conventional BCS low Tc superconductors, the pressure effect in SrxBi2Se3 is well accounted by pressure induced band broadening.

In this paper we report the preparation of single crystals of Bi2Te3 and Cr0.05(Bi2Te3)0.95 by modified Bridgman method. XRD, EDX and SEM analysis of these crystals have been done for the confirmation of the purity of the samples. Resistivity measurement from 2 K to 300 K has been done by Vander-Pauw method. We observed 20% increase in resistivity after Cr doping. Hall measurement has been done at 2 K for both the samples and we found that after Cr doping charge carrier density has increased but mobility is decreased by a factor of ∼7.9. We also provide evidence for ferromagnetism with Cr doping onto Bi2Te3.

We report superconductivity in In doped topological crystalline insulator SnTe. It shows superconducting transition with Tc-onset at 4.7K on doping 50% In at Sn site which is confirmed by both resistivity and rf susceptibility measurements. The upper critical field is found to be 1.6T. The Ginzburg Landau coherence length is estimated to be 143.5 A.

In this paper we have shown the doping effects of elements Y, F and Sb in place of RE (rare earth elements), O and As respectively in 1111-ferropnictides. We study the behavior of upper critical field and superconducting transition temperatures as a function of doping. In Ce and La based compounds maximum upper critical field was found to be 147 T and 122 T respectively. Correspondingly, the maximum transition temperature was found to be 48.6 K and 34.8 K.

We report on the superconducting properties of indium-doped SnTe. SnTe has recently been explored as a topological crystalline insulator. Single crystals of Sn0.5In0.5Te have been synthesized by a modified Bridgman method. Resistivity measurement performed in the range 1.6?300 K shows a metallic normal state with onset of superconducting transition at . Bulk superconductivity has also been confirmed by DC magnetization, AC susceptibility and rf penetration depth measurements. Zero-temperature upper critical field, lower critical field, coherence length, and penetration depth are estimated to be 1.6 T, 1 mT, 143.5 ? and 853 nm, respectively. The temperature dependence of the low-temperature penetration depth indicates S-wave fully gapped characteristics with BCS (Bardeen-Cooper-Schrieffer) gap . Hall and Seebeck coefficient measurements confirm the dominance of hole conduction with possible phonon-drag effects around . Resistive transition studied under applied magnetic field shows thermally activated flux flow behaviour.