Superconductivity in electron-doped C 60 crystals 電子ドープされたフラーレン結晶 における超伝導

1. Superconductivity in electron-doped C60crystals電子ドープされたフラーレン結晶における超伝導 Kusakabe Lab Kei Kawashima

2. Contents • Introduction • History of superconductivity • Electron-doped C60 crystals • Interesting points • Crystal structures • Electronic structures with first-principles method • Future works • Summary

3. History of superconductivity High-Tccopper oxides Electron-doped C60supeconductors The first superconductor Hg (Tc=4K) The first molecular crystalsupeconductor Ref: KURENAI : Kyoto University Research Information Repository

4. Electron-doped C60 crystals -Interesting points - • A C60 molecule itself has interesting structure. • A C60 crystalis semiconductor, and it has wide varieties of application. In addition, it transfers to a superconductor when some electrons are doped. • There are many interesting themes to study. • The types, and the number of atoms doped • Pressure dependences of electronic structure and Tc • Many C60-based crystals are BCS-type superconductor

5. Electron-doped C60 crystals - crystal structures -

6. Electron-doped C60 superconductors Cs3C60 (A15) K3C60 (FCC)

7. Tc of BCS-type superconductors Ref : Ming-Zhu Huang et al. Physical Review B, Volume 46, Number 10, 6572-6577 (1992)

8. Method for study- First principles calculation -

9. Band structures Ba6C60(BCC)-Semimetal C60(FCC)-Insurator K3C60(FCC)-Metal t1g Unoccupied t1u hu Fermi energy Occupied Ref: ・O. Gunnarsson, Reviews of Modern Physics, Vol. 68, No. 3, 575-606(1996) ・Steven C. Erwin, Phys. Rev. B, Vol. 47 No.21, 14657-14660(1993)

10. Pressure depencences K3C60(BCS-type) Cs3C60 (Non-BCS-type) Ambient Pressure Pressure =0.33GPa Pressure =4.65GPa Ref: ALEXEY Y. GANINet al. Nature Mat., Vol. 7(2008) Ref: Ming-Zhu haung et al. Phys, Rev. B, Vol. 47, NO. 13(1992)

11. Future works • I calculate the electronic structures of C60 and electron-doped C60 crystals, such as band structure, fermi-surface, and DOS, with first principles method. • After the calculations, I compare the results with those of other groups and experimental results,to analyze the electronic structures of crystals calculated.

12. Summary • A C60 crystal itself isn’t superconductor.It transfers to a superconductor when electrons are doped. • Electron-doped C60s have different electronic structure and Tc because of the differences of the type and the number of atoms doped.Electronic structure and Tc also change with applied pressure.