Tunneling Spectroscopy and Vortex Imaging in Boron- doped
Diamond Kitaoka Lab. Toshiyuki Tsuchida Ref.)B.Sacepe et al.
cond-mat/0510541 Slide 2 Contents Introduction Boron-doped Diamond
STM Measurement of Superconductor by STM Experiments Summary Slide
3 Ekimov, et al., Nature 428, 542 (2004) Synthesis under High
Pressure (8 9GPa) and High Temperature(2,800K) [HPHT Method]
Superconductivity takes place in the diamond at the interface
between graphite and B 4 C onset 4K offset 2.3K Superconductivity
in B-doped diamond Slide 4 SC in B-doped diamond film MPCVD method
Polycrystalline offset 4K onset 7K It is easy to control thickness
of diamond film growth facet Boron density Y.Takano
Appl.Phys.Lett., 85,4 2004 GAS: H 2 + CH 4 + B(CH) 3 Advantages of
this method Slide 5 J.-P. Lagrange et al. D.R.M 7 (1998) 13901393
Boron-doped diamond 3 Umezawa et al. condmat-05503303 (2005 )
B-density vs resistivity(room temperature) B-density vs Tc
Superconductivity takes place in vicinity of metal-insulator
boundary Tc of (111) film > Tc of (100) film Superconductivity
Slide 6 STM (Scanning Tunneling Microscope) 1 Observations of
microscopic geometry on the surface Measurements of local property
Atomic-scale resolution Slide 7 STM (Scanning Tunneling Microscope)
2 sample probe (normal metal) EFEF V I NNNN eV 1 V=0 V=V 1 EFEF DOS
Slide 8 STM (Scanning Tunneling Microscope) 3 sample probe (normal
metal) EFEF V I (superconductor) NN EFEF V I N S 2 /e (normal
metal) Slide 9 S.C.measurement by STM EFEF D(E) V 2 energy gap
Tunneling conductance E I/V Slide 10 Sample information 1
synthesized by MPCVD (Microwave Plasma-assisted chemical vapor
deposition ) boron density n B =1.910 21 cm -3 ( 1.1%) thickness
150 nm Umezawa et al. condmat-05503303 (2005) Slide 11 Sample
information 2 Tc is very narrow Tc onset =2.5K H c2 (T=0K)~1.5T
~150 (: coherence length) Slide 12 Surface topography by STM 600 nm
The parallel strips reflect the vicinal surface structure of the
substrate. the average of steps is ~1.8 nm (1.51.5m 2 ) substrate
600nm 1.8nm step Slide 13 Tunneling conductance at Superconducting
state (In the BCS theory,/k B Tc 1.76) 2 =285eV Slide 14
Temperature dependence of the BCS gap Tc=1.85K susceptibility and
transport BCS fitting curve indicates Tc=1.85K Tc ~ 1.9K Slide 15
Superconducting state observed by STM /k B Tc 1.74 Tc=1.85K B-doped
diamond is conventional BCS superconductor Slide 16 Vortex Type-I
Type-II HcHc 1 Hc 2 S.C. stateVortex stateNormal state Applied
magnetic field diamagnetic Superconducting state Normal state Slide
17 Vortex images H=1200OeH=1900Oe 1.5m White S.C. state Black
normal state In the higher field, more vortice exist. Comparing
with the ideal triangular vortex lattice, the vortex lattice of
B-doped diamond is inhomogeneous. because of random substitution of
Boron H. F. Hess et al,Phys.Rev.Lett. 62,214(1989) NbSe 2
d~110nmd~140nm Slide 18 Density of states around the vortex
H=1800Oe The diameter of vortex is estimated about 15nm. (c.f. GL
=15nm) Even within the BCS gap, DOS around E F exists. Slide 19
Summary First observation of SC state by STM B-doped diamond is the
conventional BCS superconductor Under magnetic field,the vortices
are arranged in disordered triangular lattice
