1,171 research outputs found
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.
Determination of the mosaic angle distribution of Grafoil platelets using continuous-wave NMR spectra
We described details of a method to estimate with good accuracy the mosaic
angle distributions of microcrystallites (platelets) in exfoliated graphite
like Grafoil which is commonly used as an adsorption substrate for helium thin
films. The method is based on analysis of resonance field shifts in
continuous-wave (CW) NMR spectra of He ferromagnetic monolayers making
use of the large nuclear polarization of the adsorbate itself. The mosaic angle
distribution of a Grafoil substrate analyzed in this way can be well fitted to
a gaussian form with a deg spread. This distribution is quite
different from the previous estimation based on neutron scattering data which
showed an unrealistically large isotropic powder-like component.Comment: 6 pages, 5 figure
Extrinsic Spin Hall Effect Induced by Iridium Impurities in Copper
We study the extrinsic spin Hall effect induced by Ir impurities in Cu by
injecting a pure spin current into a CuIr wire from a lateral spin valve
structure. While no spin Hall effect is observed without Ir impurity, the spin
Hall resistivity of CuIr increases linearly with the impurity concentration.
The spin Hall angle of CuIr, % throughout the concentration
range between 1% and 12%, is practically independent of temperature. These
results represent a clear example of predominant skew scattering extrinsic
contribution to the spin Hall effect in a nonmagnetic alloy.Comment: 5 pages, 4 figure
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.
Charge and Spin Transport at the Quantum Hall Edge of Graphene
Landau level bending near the edge of graphene, described using 2d Dirac
equation, provides a microscopic framework for understanding the quantum Hall
Effect (QHE) in this material. We review properties of the QHE edge states in
graphene, with emphasis on the novel phenomena that arise due to Dirac
character of electronic states. A method of mapping out the dispersion of the
edge states using scanning tunneling probes is proposed. The Zeeman splitting
of Landau levels is shown to create a particularly interesting situation around
the Dirac point, where it gives rise to counter-circulating modes with opposite
spin. These chiral spin modes lead to a rich variety of spin transport
phenomena, including spin Hall effect, spin filtering and injection, and
electric detection of spin current. The estimated Zeeman spin gap, enhanced by
exchange, of a few hundred Kelvin, makes graphene an attractive system for
spintronics. Comparison to recent transport measurements near nu=0 is
presented.Comment: 10 pages, 6 figures, invited pape
Spin-Echo Measurements for an Anomalous Quantum Phase of 2D Helium-3
Previous heat-capacity measurements of our group had shown the possible
existence of an anomalous quantum phase containing the zero-point vacancies
(ZPVs) in 2D He. The system is monolayer He adsorbed on graphite
preplated with monolayer He at densities () just below the 4/7
commensurate phase (). We carried out
pulsed-NMR measurements in order to examine the microscopic and dynamical
nature of this phase. The measured decay of spin echo signals shows the
non-exponential behaviour. The decay curve can be fitted with the double
exponential function, but the relative intensity of the component with a longer
time constant is small (5%) and does not depend on density and temperature,
which contradicts the macroscopic fluid and 4/7 phase coexistence model. This
slowdown is likely due to the mosaic angle spread of Grafoil substrate and the
anisotropic spin-spin relaxation time in 2D systems with respect to the
magnetic field direction. The inverse value deduced from the major echo
signal with a shorter time constant, which obeys the single exponential
function, decreases linearly with decreasing density from , supporting the
ZPV model.Comment: 4 pages, 6 figure
Magnetism as a mass term of the edge states in graphene
The magnetism by the edge states in graphene is investigated theoretically.
An instability of the pseudo-spin order of the edge states induces
ferrimagnetic order in the presence of the Coulomb interaction. Although the
next nearest-neighbor hopping can stabilize the pseudo-spin order, a strong
Coulomb interaction makes the pseudo-spin unpolarized and real spin polarized.
The magnetism of the edge states makes two peaks of the density of states in
the conduction and valence energy bands near the Fermi point. Using a
continuous model of the Weyl equation, we show that the edge-induced gauge
field and the spin dependent mass terms are keys to make the magnetism of the
edge states. A relationship between the magnetism of the edge states and the
parity anomaly is discussed.Comment: 7 pages, 5 figure
Boundary States in Graphene Heterojunctions
A new type of states in graphene-based planar heterojunctions has been
studied in the envelope wave function approximation. The condition for the
formation of these states is the intersection between the dispersion curves of
graphene and its gap modification. This type of states can also occur in smooth
graphene-based heterojunctions.Comment: 5 pages, 3 figure
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