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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 al condmat-05503303

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Contents Introduction Physical Properties of Diamond Superconductivity in diamond Experiments Summary

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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

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Band structure of Diamond Band gap 5.47eV 6.310 4 K Band gap (eV) Diamond5.47 Si1.09 Ge0.72 good insulator Semiconducting behavior by doping carrier

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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

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

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

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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

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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 :

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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 Cont:3% TMB(B/C):2000~12000ppm CVD conditions:

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Boron-doped diamond film MPCVD method Polycrystalline thin film (3.5 m ) on Si substrate Boron doped level 0.53% (Carrier Density~9.410 20 cm -3 ) Polycrystalline Si substrate offset 4K onset 7K Meissner effect

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Property of diamond film Takano et.al.Appl.Phys.Lett., 85, 4 2004 Type II superconductor H c2 (T=0K)~5.12T ~100 (: coherence length) S.C normal >>9 (average length between of boron atoms)

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

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Umezawa et al condmat-05503303 (111) epitaxial film has the higher Tc than (100) T c(offset) vs. Boron concentration

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superconductivity appears in the vicinity of metal-insulator transition resistivity at room temperature J.-P. Lagrange et al. D.R.M 7 (1998) 13901393

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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

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

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

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the property of superconductivity Zero resistivity Meissner effect Typical character

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

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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 Tc=1.7KTc=3K Tc=Tc(onset)-Tc(offset)

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