12,132 research outputs found
Fabrication of graphene nanoribbon by local anodic oxidation lithography using atomic force microscope
We conducted local anodic oxidation (LAO) lithography in single-layer,
bilayer, and multilayer graphene using tapping-mode atomic force microscope.
The width of insulating oxidized area depends systematically on the number of
graphene layers. An 800-nm-wide bar-shaped device fabricated in single-layer
graphene exhibits the half-integer quantum Hall effect. We also fabricated a
55-nm-wide graphene nanoribbon (GNR). The conductance of the GNR at the charge
neutrality point was suppressed at low temperature, which suggests the opening
of an energy gap due to lateral confinement of charge carriers. These results
show that LAO lithography is an effective technique for the fabrication of
graphene nanodevices.Comment: 4 pages, 4 figure
Using single quantum states as spin filters to study spin polarization in ferromagnets
By measuring electron tunneling between a ferromagnet and individual energy
levels in an aluminum quantum dot, we show how spin-resolved quantum states can
be used as filters to determine spin-dependent tunneling rates. We also observe
magnetic-field-dependent shifts in the magnet's electrochemical potential
relative to the dot's energy levels. The shifts vary between samples and are
generally smaller than expected from the magnet's spin-polarized density of
states. We suggest that they are affected by field-dependent charge
redistribution at the magnetic interface.Comment: 4 pages, 1 color figur
Doping evolution of the electronic structure in the single-layer cuprates BiSrLaCuO: Comparison with other single-layer cuprates
We have performed angle-resolved photoemission and core-level x-ray
photoemission studies of the single-layer cuprate
BiSrLaCuO (Bi2201) and revealed the doping
evolution of the electronic structure from the lightly-doped to optimally-doped
regions. We have observed the formation of the dispersive quasi-particle band,
evolution of the Fermi ``arc'' into the Fermi surface and the shift of the
chemical potential with hole doping as in other cuprates. The doping evolution
in Bi2201 is similar to that in CaNaCuOCl (Na-CCOC),
where a rapid chemical potential shift toward the lower Hubbard band of the
parent insulator has been observed, but is quite different from that in
LaSrCuO (LSCO), where the chemical potential does not
shift, yet the dispersive band and the Fermi arc/surface are formed around the
Fermi level already in the lightly-doped region. The (underlying) Fermi surface
shape and band dispersions are quantitatively analyzed using tight-binding fit,
and the deduced next-nearest-neighbor hopping integral also confirm the
similarity to Na-CCOC and the difference from LSCO
Spin Polarization and Magneto-Coulomb Oscillations in Ferromagnetic Single Electron Devices
The magneto-Coulomb oscillation, the single electron repopulation induced by
external magnetic field, observed in a ferromagnetic single electron transistor
is further examined in various ferromagnetic single electron devices. In case
of double- and triple-junction devices made of Ni and Co electrodes, the single
electron repopulation always occurs from Ni to Co electrodes with increasing a
magnetic field, irrespective of the configurations of the electrodes. The
period of the magneto-Coulomb oscillation is proportional to the single
electron charging energy. All these features are consistently explained by the
mechanism that the Zeeman effect induces changes of the Fermi energy of the
ferromagnetic metal having a non-zero spin polarizations. Experimentally
determined spin polarizations are negative for both Ni and Co and the magnitude
is larger for Ni than Co as expected from band calculations.Comment: 4 pages, 3 figures, uses jpsj.sty, submitted to J. Phys. Soc. Jp
Single-dot spectroscopy via elastic single-electron tunneling through a pair of coupled quantum dots
We study the electronic structure of a single self-assembled InAs quantum dot
by probing elastic single-electron tunneling through a single pair of weakly
coupled dots. In the region below pinch-off voltage, the non-linear threshold
voltage behavior provides electronic addition energies exactly as the linear,
Coulomb blockade oscillation does. By analyzing it, we identify the s and p
shell addition spectrum for up to six electrons in the single InAs dot, i.e.
one of the coupled dots. The evolution of shell addition spectrum with magnetic
field provides Fock-Darwin spectra of s and p shell.Comment: 7 pages, 3 figures, Accepted for publication in Phys. Rev. Let
Nonequilibrium spin distribution in single-electron transistor
Single-electron transistor with ferromagnetic outer electrodes and
nonmagnetic island is studied theoretically. Nonequilibrium electron spin
distribution in the island is caused by tunneling current. The dependencies of
the magnetoresistance ratio on the bias and gate voltages show the
dips which are directly related to the induced separation of Fermi levels for
electrons with different spins. Inside a dip can become negative.Comment: 11 pages, 2 eps figure
First-Principles Study on Leakage Current through Si/SiO Interface
The relationship between the presence of defects at the stacking structure of
the Si/SiO interface and leakage current is theoretically studied by
first-principles calculation. I found that the leakage current through the
interface with dangling bonds is 530 times larger than that without any
defects, which is expected to lead to dielectric breakdown. The direction of
the dangling bonds is closely related to the performance of the oxide as an
insulator. In addition, it is proved that the termination of the dangling bonds
by hydrogen atoms is effective for reducing the leakage current.Comment: 11 pages. to be published in Phys. Rev.
Dynamic nuclear polarization induced by breakdown of fractional quantum Hall effect
We study dynamic nuclear polarization (DNP) induced by breakdown of the
fractional quantum Hall (FQH) effect. We find that voltage-current
characteristics depend on current sweep rates at the quantum Hall states of
Landau level filling factors = 1, 2/3, and 1/3. The sweep rate dependence
is attributed to DNP occurring in the breakdown regime of FQH states. Results
of a pump and probe experiment show that the polarities of the DNP induced in
the breakdown regimes of the FQH states is opposite to that of the DNP induced
in the breakdown regimes of odd-integer quantum Hall states.Comment: 4 pages, 4 figure
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