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High Pressure Study on MgB 2

High Pressure Study on MgB 2. B.Lorenz, et al . Phys. Rev.B 64 ,012507(2001). Shimizu-group Naohiro Oki. Contents. Introduction ・ BCS theory ・ About MgB 2 ・ Motivation Experiment Results & Discussions My experiment Summary. Introduction. BCS theory. Phonon. 格子. Interaction

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High Pressure Study on MgB 2

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  1. High Pressure Study on MgB2 B.Lorenz, et al. Phys. Rev.B 64,012507(2001) Shimizu-group Naohiro Oki

  2. Contents • Introduction ・BCS theory ・About MgB2 ・Motivation • Experiment • Results & Discussions • My experiment • Summary

  3. Introduction BCS theory Phonon 格子 Interaction (相互作用） Electron cooper pair 電子 (cooper pair) Superconductivity In the BCS theory Materials containing light or hard elements are predicted to have HighTc. (But ～30K) http://www.phys.aoyama.ac.jp/~w3-jun/ achievements/study_sc_chara.html 超伝導転移温度

  4. 5B Boron • very light • very hard β-Boron (1Gpa～1万気圧) Tc ～ 6K (at 175GPa) not high Superconductor of elements Mikhail I. Eremets, et al. Science 293, 272 (2001) http://www.phys.aoyama.ac.jp/~w3-jun/ achievements/study_sc_type_element.html Materials containing boron High Tc? On this time, I will talk aboutMgB2.

  5. Tc ～ 39K Zero resistivity MgB2 structure Previous work Temperature dependence of electrical resistivity. http://www.phys.aoyama.ac.jp/~w3-jun/ achievements/study_sc_history_mgb2.html B : Honeycomb network layer Mg :Triangular lattice layer 蜂の巣構造 Superconductive transition • Higher than a limit of Tc of • 30K in the BCS theory. • MgB2 attracted great attention Graphite http://www.f-denshi.com/000okite/ 500metal/nanotube01.html 三角格子 J. Nagamatsu et al., Nature (London) 410, 63 (2001)

  6. Motivation For example… In the study of superconductivity, pressureapplication is a very important method. • β-Boron Pressure dependence of Tc These are rare example. Superconductor (at 175GPa) dTc/dP>0 MgB2 Mikhail I. Eremets, et al. Science 293, 272 (2001) • Hg-1223 (not BCS superconductor) increase The highest Tc ever recorded 164K （at 31GPa） pressure Tc or decrease L.Gao, et al Phys. Rev. B 50 (1994) 4260

  7. Experiment • Sample : MgB2 • Cell : Teflon • High pressure cramp : BeCu • Pressure medium : Fluorinert • Manometer : Pb • Thermometer : chromel-alumel thermocouple (300～45K) • germanium (45K～) 圧力計 温度計 圧力媒体 • Measurement of Electrical resistance Four lead technique 四端子法 Image of hydrostatic pressure 0GPa • Measurement of magnetic susceptibility 磁化率 ac : inductance method with LR-700 Bridge dc : Quantum Design SQUID magnetometer 超伝導量子干渉装置 ～1.84GPa Hydrostatic pressure 静水圧

  8. Result & Discussion.1 Temperature dependence of electrical resistivity. 0GPa 電気抵抗率 Zero resistivity • 300K～40K : The ρ decreased like a metal on cooling • 39K : The ρ started to drop rapidly Superconductivity transition

  9. 交流磁化率 37.4K 38.5K Result & discussion.2 Temperature dependence of ac magnetic susceptibility at various pressure. pressure Tc: midpoint of transition. • Pressure effect on Tc is determined ac magnetic susceptibility.( ～1.84GPa) • Superconducting transition is shifted toward low temperature.

  10. Result & Discussion.3 Pressure dependence of Tc 1～8 : Run number This result is good agreement with the calculated value in BCS framework. (dTc/dP = -1.4K/GPa) dTc/dP = -1.6K/Gpa Tc of MgB2 decreased with pressure applying.

  11. C C C C C C C C C C C - C B + C C C My experiment Diamond Boron-Doped Diamond (BDD) Boron Doping Semiconductor Metal Insulator E.A.Ekimov, et al. Nature (London) 428,542(2004) Tc ～ 4K Superconductor BDD pressure increase Tc or decrease

  12. Summary • Pressure plays very important role in the study of superconductivity. • Unfortunately, Tc of MgB2 decreased with pressure applying. • My experimental purpose is to observe the pressure effect on Tc in Boron-Doped Diamond.

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