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

2. Outline Introduction Motivation Experimental Findings Conclusion Next Plan

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

4. pressure 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! What happens when we apply pressure?

5. High Pressure!! ( ～ 350 GPa) R = 6400 km M = 5.97 x 10 24 kg Centre of Earth ～ 350 GPa 3 cm 6 cm Diamond Anvil Cell (DAC) 1 GPa = 10 9 Pa ～ 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! Critical Temperature Superconductivity!! Resistance = 0 Meissner Effect Decrease in Temperature Decrease in energy and thermal vibrations Decrease in resistance !!!

8. How to estimate pressure Ruby produces fluorescence when irradiated by laser. The wavelength of the peak changes with pressure. For P < 100 GPa : Ruby Fluorescence （ルビー蛍光 法） For P > 100 GPa : Raman Spectroscopy ( ラマン分光法） P = 66.9 - 0.5281ν + 3.585×10 -4 ν 2 Irradiate diamond with laser. On applying pressure, the vibration of C-C bond in diamond changes, the wavelength of scattered light becomes small.

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 upto T c = 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 (a)Na T c = 18.1 K Superconductivity in electron-doped layered TiNCL, Shuai Zhang et al, Physical Review B 86 (2012)

15. Experimental Findings (b)K T c = 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 T c ∝ 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