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Superconductivity in Diamond Kitaoka Lab. Toshiyuki Tsuchida Ref.) Ekimov, et al., Nature 428, 542 (2004) Y.Takano Appl.Phys.Lett., 85,4 2004 Umezawa et.

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Presentation on theme: "Superconductivity in Diamond Kitaoka Lab. Toshiyuki Tsuchida Ref.) Ekimov, et al., Nature 428, 542 (2004) Y.Takano Appl.Phys.Lett., 85,4 2004 Umezawa et."— Presentation transcript:

1 Superconductivity in Diamond Kitaoka Lab. Toshiyuki Tsuchida Ref.) Ekimov, et al., Nature 428, 542 (2004) Y.Takano Appl.Phys.Lett., 85, Umezawa et al . condmat

2 Contents Introduction – Physical Properties of Diamond – Superconductivity in diamond Experiments Summary

3 Physical Properties of Diamond Covalent bonding crystal (sp3 hybrid orbital) ⇒ strong bonding energy hardest material chemically stable material high thermal conductivity Bonding energy (ev) Diamond7.38 Si5.81 Ge3.88

4 Band structure of Diamond Band gap 5.47eV ~ 6.3×10 4 K Band gap (eV) Diamond5.47 Si1.09 Ge0.72 good insulator Semiconducting behavior by doping carrier

5 Carrier doping to diamond making a shallow acceptor level close to top of the valence band hole dope(acceptor) Electron dope(donor) Carrier doping B 3+ -doping N 5+ -doping p-type(hole) n-type(electron) low carrier doping level →semiconducting conductivity high carrier doping level →metallic-like conductivity Eg E Valence Band Conduction band Acceptor level

6 Ekimov, et al., Nature 428, 542 (2004) onset 4K offset 2.3K Discovery of superconductivity in Diamond

7 Application Diamond B-doping hardest material chemically stable material high thermal conductivity Electronic property metalinsulatorsemiconductorsuperconductor hybrid electronic device

8 Ekimov, et al., Nature 428, 542 (2004) Synthesis under high pressure (8 ~ 9GPa) and high temperature(2,800K) Superconductivity takes place in the diamond at the interface between graphite and B 4 C onset 4K offset 2.3K

9 onset 4K offset 2.3Ksuperconductor At 2.3K,the sample shows Meissner effect (perfect diamagnetism) the onset of perfect diamagnetism corresponds to zero resistance. perfect diamagnetism : 完全反磁性

10 Another approach (CVD method) Synthesis of Diamond 1. under high pressure and high temperature 2. MP-CVD method (film) Pressure: 60 Torr Microwave power:600W Depositing time:8hrs Substrate: ・ Si(100)* ・ Single crystalline type Ib Diamond (111) and (100) GAS: H 2 + CH 4 + TMB CH 4 Cont:3% TMB(B/C):2000~12000ppm CVD conditions:

11 Boron-doped diamond film MPCVD method Polycrystalline thin film (3.5 μm ) on Si substrate Boron doped level ~ 0.53% (Carrier Density~9.4×10 20 cm -3 ) Polycrystalline Si substrate offset 4K onset 7K Meissner effect

12 Property of diamond film Takano et.al.Appl.Phys.Lett., 85, Type II superconductor H c2 (T=0K)~5.12T →ξ~100 Å (ξ: coherence length) S.C normal >>9 Å (average length between of boron atoms)

13 (100) Homoepitaxial film bus ΔTc is very narrow Tc(onset)=2.5K Bustarret.et al. PRL,93,237005(2004)

14 Umezawa et al . condmat (111) epitaxial film has the higher Tc than (100) T c(offset) vs. Boron concentration

15 superconductivity appears in the vicinity of metal-insulator transition resistivity at room temperature J.-P. Lagrange et al. D.R.M 7 (1998) 1390–1393

16 Summary Discovery of the superconductivity in the Boron- doped diamond by high pressure method and MPCVD method (111) epitaxial film has the higher Tc than (100) The superconductivity in diamond takes place in vicinity of metal-insulator transition

17 Θ:Debye Temperature ω D : Debye frequency κ : Thermal conductivity C : specific heat v : velocity l : mean free path

18 ξ

19 Averaged distance of B-B Boron atom is surrounded by about 6carbon atoms ⇒ averaged distance of B-B ~ 9 Å << ξ Electron can have many partners of the cooper-pair

20 the property of superconductivity ・ Zero resistivity ・ Meissner effect Typical character

21 HcHc H c2 H H c1 Type-I Type-II Type-I and Type-II superconductor

22 Comparing sample by different methods Ekimov, et al., Nature 428, 542 (2004) Yoshihiko Takano et.al.. Appl.Phys.Lett.,Vol 85,No.14,4 October 2004 (111)-oriented thin film ΔTc=1.7KΔTc=3K ΔTc=Tc(onset)-Tc(offset)

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