2,240 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
Effect of aromatic hydrocarbon addition on in situ powder-in-tube processed MgB2 tapes
We fabricated in situ powder-in-tube processed MgB2/Fe tapes using aromatic
hydrocarbon of benzene, naphthalene, and thiophene as additives, and
investigated the superconducting properties. We found that these aromatic
hydrocarbons were very effective for increasing the Jc values. The Jc values of
20mol% benzene-added tapes reached 130A/mm2 at 4.2K and 10T. This value was
almost comparable to that of 10mol% SiC-added tapes and about four times higher
than that of tapes with no additions. Microstructure analyses suggest that this
Jc enhancement is due to both the substitution of carbon for boron in MgB2 and
the smaller MgB2 grain size.Comment: 6 pages, 4 figure
Local magnetic anisotropy in BaFeAs: a polarized inelastic neutron scattering study
The anisotropy of the magnetic excitations in BaFeAs was studied by
polarized inelastic neutron scattering which allows one to separate the
components of the magnetic response. Despite the in-plane orientation of the
static ordered moment we find the in-plane polarized magnons to exhibit a
larger gap than the out-of-plane polarized ones indicating very strong
single-ion anisotropy within the layers. It costs more energy to rotate a spin
within the orthorhombic {\it a-b} plane than rotating it perpendicular to the
FeAs layers.Comment: 4 pages, 4 figure
Spin transport through a single self-assembled InAs quantum dot with ferromagnetic leads
We have fabricated a lateral double barrier magnetic tunnel junction (MTJ)
which consists of a single self-assembled InAs quantum dot (QD) with
ferromagnetic Co leads. The MTJ shows clear hysteretic tunnel magnetoresistance
(TMR) effect, which is evidence for spin transport through a single
semiconductor QD. The TMR ratio and the curve shapes are varied by changing the
gate voltage.Comment: 4 pages, 3 figure
Kondo Universal Scaling for a Quantum Dot Coupled to Superconducting Leads
We study competition between the Kondo effect and superconductivity in a
single self-assembled InAs quantum dot contacted with Al lateral electrodes.
Due to Kondo enhancement of Andreev reflections the zero-bias anomaly develops
sidepeaks, separated by the superconducting gap energy Delta. For ten valleys
of different Kondo temperature T_K we tune the gap Delta with an external
magnetic field. We find that the zero-bias conductance in each case collapses
onto a single curve with Delta/kT_K as the only relevant energy scale,
providing experimental evidence for universal scaling in this system.Comment: 4 pages, 3 figure
Randomly Diluted e_g Orbital-Ordered Systems
Dilution effects on the long-range ordered state of the doubly degenerate
orbital are investigated. Quenched impurities without the orbital degree
of freedom are introduced in the orbital model where the long-range order is
realized by the order-from-disorder mechanism. It is shown by the Monte-Carlo
simulation and the cluster-expansion method that a decrease in the orbital
ordering temperature by dilution is remarkable in comparison with that in the
randomly diluted spin models. Tiltings of orbitals around impurity cause this
unique dilution effects on the orbital systems. The present theory provides a
new view point for the recent experiments in KCuZnF.Comment: 4 pages, 4 figure
Electrical control of Kondo effect and superconducting transport in a side-gated InAs quantum dot Josephson junction
We measure the non-dissipative supercurrent in a single InAs self-assembled
quantum dot (QD) coupled to superconducting leads. The QD occupation is both
tuned by a back-gate electrode and lateral side-gate. The geometry of the
side-gate allows tuning of the QD-lead tunnel coupling in a region of constant
electron number with appropriate orbital state. Using the side-gate effect we
study the competition between Kondo correlations and superconducting pairing on
the QD, observing a decrease in the supercurrent when the Kondo temperature is
reduced below the superconducting energy gap in qualitative agreement with
theoretical predictions
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