Session U4: NM.3 Novel Properties III

Pressure Induced Superconductivity in Topological Compounds

Topological quantum compounds attract worldwide attention because of many novel physical properties. Topological superconductivity is one of most excited topological quantum states since its surface supports Majorana fermions [1] that are assumed many new physics. We found superconductivity can be realized in a typical topological insulator Bi$_{2}$Te$_{3}$ induced via pressure above 3 GPa where the surface remains gapless Dirac cone[8]. The Hall coefficient measurements indicated carriers evolved as function of pressure. The x ray diffraction experiments at high pressure indicated that Bi$_{2}$Te$_{3}$ keeps stable up to 8GPa. This strongly suggests that the superconductivity observed in Bi$_{2}$Te$_{3}$ ambient phase is topological related. Acknowledgments: This work was supported by nsf {\&} MOST of China. \\[4pt] References\\[0pt] [1] 1. B. A. Bernevig et al, Science \textbf{314}, 1757 (2006).\\[0pt] [2] H. J. Zhang et al., Nature Physics \textbf{5,} 438 (2009).\\[0pt] [3] Y. Xia et al., Nature Physics \textbf{5,} 398 (2009).\\[0pt] [4] Y.-L. Chen et al., Science \textbf{325}, 178 (2009).\\[0pt] [5] Y. S. Hor et al., Phys. Rev. Lett.\textbf{104,} 57001 (2010).\\[0pt] [6] M. Einaga et al., Journal of Physics: Conference Series\textbf{ 215}, 012036(2010).\\[0pt] [7] M. Einaga et al, arXiv: 1012.4932v1 (2010).\\[0pt] [8] J. L. Zhang et al., Proc. Natl Acad. Sci. \textbf{108}, 24 (2011).   

High Pressure High Temperature Devitrification of Iron-Based Metallic Glass

High pressure high temperature devitrification of Fe$_{78}$B$_{13}$Si$_{9}$ metallic glass was studied by \textit{in situ} energy dispersive x-ray powder diffraction measurements at HPCAT beamline 16BM-B, APS utilizing a portable Paris Edinburg cell with an integrated graphite heater. Structural changes were measured using sequential 20 second EDXD spectrums with white beam synchrotron x-ray incident radiation source. The iron-based metal glass sample along with MgO pressure standard was first pressurized and then heated at a constant rate of 2.5 K/min. Onset crystallization temperature is taken as the point where crystal peaks become apparent in the x-ray spectrum at twice the intensity of spectral noise. Heating is continued until the amorphous profile of the glass give way completely to crystalline peaks. This procedure was repeated for 0.2, 1.0, 2.0, 3.0, 4.5 and 6.0 GPa. The sample showed a marked increase in the onset of crystallization temperature with pressure, with 783 K at 0.2 GPa to 873 K at 6.0 GPa. The first phase to precipitate in each case is a bcc iron phase and other iron-boron and iron-silicon phases appeared at higher temperatures. The possibility of nucleating nanocrystalline phase was also investigated with the aim of forming a nano-composite material with enhanced mechanical properties.   

A novel assembly used for hot-shock consolidation

A novel assembly characterized by an automatic set-up was developed for hot-shock consolidations of powders. The under-water shock wave and the high-temperature preheating, which are considered as two effective ways to eliminate cracks, were combined in the system. In this work, a SHS reaction mixture was used as chemical furnace to preheat the precursor powder, and the water column as well as the explosive attached to it was detached from the furnace by a solenoid valve fixed on the slide guide. When the precursor powders was preheated to the designed temperature, the solenoid valve was switched on, then the water column and the explosive slid down along the slide guide by gravity. At the moment the water container contacted with the lower part, the explosive was initiated, and the generated shock wave propagated through the water column to compact the powders. So the explosive and water column can be kept cool during the preheating process. The intensity of shock wave loading can be adjusted by changing the heights of water column. And the preheating temperature is controlled in the range of 700$\sim$1300$^{\circ}$C by changing the mass of the SHS mixture. In this work, pure tungsten powders and tungsten-copper mixture were separately compacted using this new assembly. The pure tungsten powder with a grain size of 2$\mu $m were compacted to high density (96{\%}T.D.) at 1300$^{\circ}$C, and the 90W-10Cu (wt pct) mixtures were compacted to nearly theoretical density at 1000$^{\circ}$C. The results showed that both samples were free of cracks. The consolidated specimens were then characterized by SEM analysis and micro-hardness testing.