Search for high temperature superconductivity of Sr 2 VO 4 under high pressure

1. Search for high temperature superconductivity of Sr2VO4 under high pressure Shimizu Lab KaideNaohiro

2. Contents • Introduction : Mott insulator La2CuO4 • Sr2VO4 • Research • Summary

3. Introduction

4. Metal, semiconductor, insulator “insulator” “metal” “semiconductor” ρ (Ω cm) Aluminium  Quartz Gold Silicon Germanium

5. Mott insulator The definition : Mott insulator are a class of materials that should conduct electricity under conventional band theories, but are insulators when measured. This effect is due to electron–electron interactions, which are not considered in conventional band theory. ・ What is the difference between metal and insulator ? → Band theory, R v.s. T… ・ What is electron–electron interactions ? → On-site coulomb interaction U

6. Band theories ε “metal” “insulator” ε εF εF D(ε) D(ε) D(ε) : density of states : electron

7. The temperature dependence of resistivity “metal” “insulator” positive negative ρ (Ω cm) ρ (Ω cm) T (K) T (K)

8. Correlated electron effects In case of U >> t, Electron is localized. t : kinetic energy of electron U : On-site coulomb interaction U http://www.kh.phys.waseda.ac.jp/thesis/m_s_adachihara.pdf

9. Mott insulator The definition : Mott insulator are a class of materials that should conduct electricity under conventional band theories, but are insulators when measured. This effect is due to electron–electron interactions, which are not considered in conventional band theory. ε ρ (Ω cm) T (K) D(ε)

10. （ex） La2CuO4 ・ Layered perovskite ・ d9Mottinsulator Cu La Ba O Sr Ca J. G. Bednorz et al., Science. 236 (4797) , 73 -75 (1987).

11. Crystal field Cu 3d9 eg (ex)La2CuO4 3d dzx dxy dyz t2g d3z^2 - r^2 dx^2 –y^2 O Crystal field Cu

12. Jahn-Teller effect dx^2 –y^2 eg d3z^2 - r^2 Jahn-Teller effect O Cu stable

13. The strong on-site Coulomb repulsion U V （ex）La2CuO4 E E Cu 3d9 eg ・Half-filledstate ・ The strong on-site Coulomb repulsion U →Mott insulator （ usuallyantiferromagnet） large 3d EF Sr U On-site coulomb interaction U t2g EF O Crystal field U Jahn-Teller effect Crystal structure of La2CuO4 C. Chailloutet al., PhysicaC 158, 183 (1989)

14. Sr2VO4

15. Sr2VO4 V ・Layered perovskite (as La2CuO4) ・d1Mottinsulator (t2g state) Sr O 空間群　I4/mmm(No.139)

16. Electric resistance (at ambient pressure) insulator ρ(Ωcm) T (K) V. Giannakopoulou et al , Solid State Communications, Vol. Y3, No. 7, pp. 57Y-5X3, lYY5 (1995)

17. Motivation （ex）La2CuO4 V 3d1 Pressure increasing Cu 3d9 eg eg 3d 3d High Tcsuperconductivity?? t2g t2g dyz,, dzx Crystal field U dxy U Uniaxial pressure

18. Research

19. How to make high pressure :Sr2VO4(single crystal) diamond insulator ・sample: Sr2VO4 ・culet: 200μm ・gasket : Re • ・usinga film ・insulator : c-BN • 4-terminal method Pt Pt Ruby film gasket Cu On the film

20. Result ・ The slope of resistivity is suppressed. ・It is expected that resistivity measurements reveals M-I transition at about 50 GPa. ・ Superconductivity was not observed. Fig. Temperature dependence of electrical resistance (normalized at 250 K) at pressure of 15- 41 GPa.

21. Summary

22. Summary • Applying pressure on Sr2VO4, the slope of resistivity is suppressed. • It is expected that resistivity measurements reveals M-I transition at about 50 GPa in Sr2VO4. • Superconductivity was not observed.

23. ρv.s. P