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M1 Colloquium Presentation

M1 Colloquium Presentation. Superconductivity in MNX type compounds ( TiNCl ). Arora Varun 29A13106 (Shimizu Lab). Superconducting Nitride Halides (MNX), Christian M. Schurz et al. , Zeitschrift for Kristallographie 226 , 395-416 (2011). Outline. Introduction Motivation

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M1 Colloquium Presentation

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  1. M1 Colloquium Presentation Superconductivity in MNX type compounds( TiNCl ) AroraVarun 29A13106 (Shimizu Lab) Superconducting Nitride Halides (MNX), Christian M. Schurz et al. , Zeitschrift for Kristallographie226, 395-416 (2011)

  2. Outline • Introduction • Motivation • Experimental Findings • Conclusion • Next Plan

  3. Introduction • What is Kyokugen? （極限） High Pressure 　　　　高圧 Strong Magnetic Field 強磁場 Low Temperature 低温

  4. Pressure • What happens when we apply pressure? • Pressure is one of the important physical quantity. • Volume decreases! • Inter-atomic distance decreases! • Interactions between atoms and electrons change => Changes in electronic states! pressure

  5. High Pressure!! (～350 GPa) 3 cm 6 cm R = 6400 km M = 5.97 x 10 24 kg Centre of Earth ～ 350 GPa Diamond Anvil Cell (DAC) 1 GPa = 109Pa ～10000 atm (1万気圧）

  6. DAC • Why use Diamond? • Hard • Transparent

  7. What happens at Low Temperature!! Resistance in a metal stems from scattering of electrons because of thermal vibrations! Decrease in Temperature Decrease in energy and thermal vibrations Decrease in resistance !!! Critical Temperature Superconductivity!! • Resistance = 0 • Meissner Effect

  8. How to estimate pressure For P < 100 GPa : Ruby Fluorescence（ルビー蛍光法） Ruby produces fluorescence when irradiated by laser. The wavelength of the peak changes with pressure. For P > 100 GPa : Raman Spectroscopy (ラマン分光法） Irradiate diamond with laser. On applying pressure, the vibration of C-C bond in diamond changes, the wavelength of scattered light becomes small. P = 66.9 - 0.5281ν + 3.585×10-4 ν2

  9. MNX Compound(TiNCl)

  10. Introduction • MNX M : Group IV metal ( Ti, Zr, Hf ) N : Nitrogen X : Halogen ( Cl, Br, I ) • Two types of layer-structured polymorphs of MNX ： • α-form(Orthorhombic ) • β-form ( Rhombohedra ) • Superconductivity uptoTc = 25.5 K in β-form :- • Lithium doped ZrNCl : Superconductivity at 13 K (1996) • Lithium doped HfNCl : Superconductivity at 25.5 K (1998)

  11. TiNCl • α-MNX type structure • Layer Structure • [MN]+ layer is sandwiched between two sheets of halide anions [X]- • Orthorhombic Structure • Sensitive to moisture • Energy Band = 1.7 eV • (Semi-conductor) Basal Spacing

  12. Motivation for TiNCl • Potentiality of Intercalation • Since TiNCl is a layer structured compund, metal atoms/organic molecules can be inter-calated in the Van-der Walls gap between the layers • Similar structure as FeOCl • FeOCl also forms intercalation compounds with alkali metals as well as amines • Upon intercalation with pyridines, the electrical conductivity has been seen to increase drastically in FeOCl

  13. What is Inter-calation? • To insert something between elements or layers. • Dopants can be introduced through the interlayer space without substituting or disturbing the original network for electron transport. • Two types of layer structured crystals : Molecular - Van der Walls force ( eg : Graphite ) Ion – exchangeable - Redox reaction ( eg : clay minerals )

  14. Experimental Findings • Na Tc = 18.1 K Superconductivity in electron-doped layered TiNCL, Shuai Zhang et al, Physical Review B 86 (2012)

  15. Experimental Findings • K Tc = 16.1 K Structure and superconductivity of the intercalation compunds of TiNCl, Shoji Yamanaka et al, Journals of Material Chemistry (2008)

  16. Why Inter-calated TiNCl exhibits superconductivity • NOT a conventional BCS superconductor since the electron carrier concentration is very low, and the electron-phonon coupling constant observed is also too small to explain the relatively high Tc Tc∝exp[-1/N(0)V] • Proposed reason is “Structural changes due to Inter-calation”

  17. Conclusions • Like other layer structures, α-MNX also has the potential for high Tc superconductivity • β- MNX type compounds have been found to exhibit superconductivity, so there is a vast scope possible for superconductivity in α-MNX type compounds as well • TiNCl contain versatile and flexile metal nitride layers for chemical modifications via Inter-calation • TiNCl inter-calated with various metals or organic compunds exhibits moderately high Tc superconductivity (around 16.3 K). Experimental findings have also supported theoretical values

  18. Next Plan • By applying pressure as well, we can expect a change in Tc for such an intercalated compound. • By controlling doping concentration or by using different kinds of dopants with TiNCl, we have can get even more results for such unconventional superconductors

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