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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. Contents. Introduction Physical Properties of Diamond Superconductivity in diamond
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Superconductivity in Diamond Kitaoka Lab. Toshiyuki Tsuchida Ref.) Ekimov, et al., Nature 428, 542 (2004) Y.TakanoAppl .Phys.Lett., 85,4 2004 Umezawa et al．condmat-05503303
Contents • Introduction • Physical Properties of Diamond • Superconductivity in diamond • Experiments • Summary
Physical Properties of Diamond Covalent bonding crystal (sp3 hybrid orbital) ⇒ strong bonding energy hardest material chemically stable material high thermal conductivity
Band structure of Diamond Band gap 5.47eV ～ 6.3×104K good insulator Semiconducting behavior by doping carrier
Carrier doping to diamond E Conduction band Eg Acceptor level Valence Band Carrier doping B3+-doping N5+-doping p-type(hole) n-type(electron) making a shallow acceptor level close to top of the valence band hole dope(acceptor) low carrier doping level →semiconducting conductivity high carrier doping level →metallic-like conductivity Electron dope(donor)
Discovery of superconductivity in Diamond onset 4K offset 2.3K Ekimov, et al., Nature 428, 542 (2004)
Application hardest material chemically stable material high thermal conductivity Electronic property Diamond insulator semiconductor superconductor metal B-doping hybrid electronic device
onset 4K offset 2.3K Superconductivity takes place in the diamond at the interface between graphite and B4C Ekimov, et al., Nature 428, 542 (2004) Synthesis under high pressure (8～9GPa) and high temperature(2,800K)
onset 4K offset 2.3K superconductor 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
Another approach (CVD method) Synthesis of Diamond 1. under high pressure and high temperature 2. MP-CVD method (film) CVD conditions: GAS: H2 + CH4 + TMB CH４Cont:3% TMB(B/C):2000~12000ppm Substrate: ・Si(100)* ・Single crystalline type Ib Diamond (111) and (100) Pressure: 60 Torr Microwave power:600W Depositing time:8hrs
Meissnereffect Boron-doped diamond film MPCVD method onset 7K Polycrystalline offset 4K Si substrate Polycrystalline thin film (3.5 μm) on Si substrate Boron doped level ～0.53% (Carrier Density~9.4×1020cm-3)
normal S.C Property of diamond film Type II superconductor Hc2(T=0K)~5.12T →ξ~100Å (ξ: coherence length) >>9Å(average length between of boron atoms) Takano et.al.Appl .Phys.Lett., 85, 4 2004
(100) Homoepitaxial film bus Bustarret.et al. PRL,93,237005(2004) Tc(onset)=2.5K ΔTc is very narrow
Tc(offset) vs. Boron concentration (111) epitaxial film has the higher Tc than (100) Umezawa et al．condmat-05503303
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
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
Θ:Debye Temperature ωD：Debye frequency κ：Thermal conductivity C：specific heat v ：velocity l： mean free path
Averaged distance of B-B Boron atom is surrounded by about 6carbon atoms ⇒averaged distance of B-B ～9Å ＜＜ξ Electron can have many partners of the cooper-pair
Typical character ・Zero resistivity ・Meissner effect the property of superconductivity
Type-I Type-II H Hc1 Hc Hc2 Type-I and Type-II superconductor
Comparing sample by different methods Yoshihiko Takano et.al.. Appl .Phys.Lett.,Vol 85,No.14,4 October 2004 Ekimov, et al., Nature 428, 542 (2004) (111)-oriented thin film ΔTc=1.7K ΔTc=3K ΔTc=Tc(onset)-Tc(offset)
