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Localized Distributions of Quasi Two-Dimensional Electronic States near Defects Artificially Created at Graphite Surfaces in Magnetic Fields
We measured the local density of states of a quasi two-dimensional electron
system (2DES) near defects, artificially created by Ar-ion sputtering, on
surfaces of highly oriented pyrolytic graphite (HOPG) with scanning tunneling
spectroscopy (STS) in high magnetic fields. At valley energies of the Landau
level spectrum, we found two typical localized distributions of the 2DES
depending on the defects. These are new types of distributions which are not
observed in the previous STS work at the HOPG surface near a point defect [Y.
Niimi \textit{et al}., Phys. Rev. Lett. {\bf 97}, 236804 (2006).]. With
increasing energy, we observed gradual transformation from the localized
distributions to the extended ones as expected for the integer quantum Hall
state. We show that the defect potential depth is responsible for the two
localized distributions from comparison with theoretical calculations.Comment: 4 pages, 3 figure
Indication of intrinsic spin Hall effect in 4d and 5d transition metals
We have investigated spin Hall effects in 4 and 5 transition metals,
Nb, Ta, Mo, Pd and Pt, by incorporating the spin absorption method in the
lateral spin valve structure; where large spin current preferably relaxes into
the transition metals, exhibiting strong spin-orbit interactions. Thereby
nonlocal spin valve measurements enable us to evaluate their spin Hall
conductivities. The sign of the spin Hall conductivity changes systematically
depending on the number of electrons. This tendency is in good agreement
with the recent theoretical calculation based on the intrinsic spin Hall
effect.Comment: 5 pages, 4 figure
Temperature dependence of the impurity-induced resonant state in Zn-doped Bi_2Sr_2CaCu_2O by Scanning Tunneling Spectroscopy
We report on the temperature dependence of the impurity-induced resonant
state in Zn-doped Bi_2Sr_2CaCu_2O by scanning tunneling
spectroscopy at 30 mK < T < 52 K. It is known that a Zn impurity induces a
sharp resonant peak in tunnel spectrum at an energy close to the Fermi level.
We observed that the resonant peak survives up to 52 K. The peak broadens with
increasing temperature, which is explained by the thermal effect. This result
provides information to understand the origin of the resonant peak.Comment: 4 pages, 3 figures, to appear in Phys. Rev.
Micropropagation of Vitis amurensis Rupr.: An improved protocol
Research NoteAn efficient micropropagation procedure of V. amurensis cv. Zuoshan 1 was established. NAA combined with BA resulted in callus formation and inhibition of shoot growth, whereas a combination of 0.3 M IAA and 4.4 M BA gave highest shoot growth and multiplication. IAA at 2.8 and 5.7 M led to high root formation of shoots. 30 g l-1 sucrose was needed for high shoot growth, while high rooting was achieved with 0-20 g l-1 sucrose. Intact leaves are required for a high level of shoot rooting.
Scanning tunneling microscopy and spectroscopy studies of graphite edges
We studied experimentally and theoretically the electronic local density of
states (LDOS) near single step edges at the surface of exfoliated graphite. In
scanning tunneling microscopy measurements, we observed the and honeycomb superstructures extending over 34 nm
both from the zigzag and armchair edges. Calculations based on a
density-functional derived non-orthogonal tight-binding model show that these
superstructures can coexist if the two types of edges admix each other in real
graphite step edges. Scanning tunneling spectroscopy measurements near the
zigzag edge reveal a clear peak in the LDOS at an energy below the Fermi energy
by 20 meV. No such a peak was observed near the armchair edge. We concluded
that this peak corresponds to the "edge state" theoretically predicted for
graphene ribbons, since a similar prominent LDOS peak due to the edge state is
obtained by the first principles calculations.Comment: 4 pages, 6 figures, APF9, Appl. Surf. Sci. \bf{241}, 43 (2005
STS Observations of Landau Levels at Graphite Surfaces
Scanning tunneling spectroscopy measurements were made on surfaces of two
different kinds of graphite samples, Kish graphite and highly oriented
pyrolytic graphite (HOPG), at very low temperatures and in high magnetic
fields. We observed a series of peaks in the tunnel spectra, which grow with
increasing field, both at positive and negative bias voltages. These are
associated with Landau quantization of the quasi two-dimensional electrons and
holes in graphite in magnetic fields perpendicular to the basal plane. Almost
field independent Landau levels fixed near the Fermi energy, which are
characteristic of the graphite crystalline structure, were directly observed
for the first time. Calculations of the local density of states at the graphite
surfaces allow us to identify Kish graphite as bulk graphite and HOPG as
graphite with finite thickness effectively
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