5,233 research outputs found
Infrared spectroscopy of Landau levels in graphene
We report infrared studies of the Landau level (LL) transitions in single
layer graphene. Our specimens are density tunable and show \textit{in situ}
half-integer quantum Hall plateaus. Infrared transmission is measured in
magnetic fields up to B=18 T at selected LL fillings. Resonances between hole
LLs and electron LLs, as well as resonances between hole and electron LLs are
resolved. Their transition energies are proportional to and the
deduced band velocity is m/s. The lack of
precise scaling between different LL transitions indicates considerable
contributions of many-particle effects to the infrared transition energies.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let
Perturbation Calculation of the Axial Anomaly of a Ginsparg-Wilson lattice Dirac operator
A recent proposal suggests that even if a Ginsparg-Wilson lattice Dirac
operator does not possess any topological zero modes in
topologically-nontrivial gauge backgrounds, it can reproduce correct axial
anomaly for sufficiently smooth gauge configurations, provided that it is
exponentially-local, doublers-free, and has correct continuum behavior. In this
paper, we calculate the axial anomaly of this lattice Dirac operator in weak
coupling perturbation theory, and show that it recovers the topological charge
density in the continuum limit.Comment: 25 pages, v2: calculation up to O(g^4) for nonabelian gauge
backgroun
Switching Mechanism in Single-Layer Molybdenum Disulfide Transistors: an Insight into Current Flow across Schottky Barriers
In this article, we study the properties of metal contacts to single-layer
molybdenum disulfide (MoS2) crystals, revealing the nature of switching
mechanism in MoS2 transistors. On investigating transistor behavior as contact
length changes, we find that the contact resistivity for metal/MoS2 junctions
is defined by contact area instead of contact width. The minimum gate dependent
transfer length is ~0.63 {\mu}m in the on-state for metal (Ti) contacted
single-layer MoS2. These results reveal that MoS2 transistors are Schottky
barrier transistors, where the on/off states are switched by the tuning the
Schottky barriers at contacts. The effective barrier heights for source and
drain barriers are primarily controlled by gate and drain biases, respectively.
We discuss the drain induced barrier narrowing effect for short channel
devices, which may reduce the influence of large contact resistance for MoS2
Schottky barrier transistors at the channel length scaling limit.Comment: ACS Nano, ASAP (2013
Long-lived neutral-kaon flux measurement for the KOTO experiment
The KOTO ( at Tokai) experiment aims to observe the CP-violating rare
decay by using a long-lived neutral-kaon
beam produced by the 30 GeV proton beam at the Japan Proton Accelerator
Research Complex. The flux is an essential parameter for the measurement
of the branching fraction. Three neutral decay modes, , , and were used to
measure the flux in the beam line in the 2013 KOTO engineering run. A
Monte Carlo simulation was used to estimate the detector acceptance for these
decays. Agreement was found between the simulation model and the experimental
data, and the remaining systematic uncertainty was estimated at the 1.4\%
level. The flux was measured as per protons on a
66-mm-long Au target.Comment: 27 pages, 16 figures. To be appeared in Progress of Theoretical and
Experimental Physic
Bosonic t-J Model in a stacked triangular lattice and its phase diagram
In this paper, we study phase diagram of a system of two-component hard-core
bosons with nearest-neighbor (NN) pseudo-spin antiferromagnetic (AF)
interactions in a stacked triangular lattice. Hamiltonian of the system
contains three parameters one of which is the hopping amplitude between NN
sites, and the other two are the NN pseudo-spin exchange interaction and
the one that measures anisotropy of pseudo-spin interactions. We investigate
the system by means of the Monte-Carlo simulations and clarify the
low-temperature phase diagram. In particular, we are interested in how the
competing orders, i.e., AF order and superfluidity, are realized, and also
whether supersolid forms as a result of hole doping into the state of the
pseudo-spin pattern with the structure.Comment: 18 pages, 17 figures, Version to appear in J.Phys.Soc.Jp
Interaction-induced shift of the cyclotron resonance of graphene using infrared spectroscopy
We report a study of the cyclotron resonance (CR) transitions to and from the
unusual Landau level (LL) in monolayer graphene. Unexpectedly, we find
the CR transition energy exhibits large (up to 10%) and non-monotonic shifts as
a function of the LL filling factor, with the energy being largest at
half-filling of the level. The magnitude of these shifts, and their
magnetic field dependence, suggests that an interaction-enhanced energy gap
opens in the level at high magnetic fields. Such interaction effects
normally have limited impact on the CR due to Kohn's theorem [W. Kohn, Phys.
Rev. {\bf 123}, 1242 (1961)], which does not apply in graphene as a consequence
of the underlying linear band structure.Comment: 4 pages, 4 figures. Version 2, edited for publication. Includes a
number of edits for clarity; also added a paragraph contrasting our work w/
previous CR expts. in 2D Si and GaA
Search for the decay
We performed a search for the decay with the
E391a detector at KEK. In the data accumulated in 2005, no event was observed
in the signal region. Based on the assumption of
proceeding via parity-violation, we obtained the single event sensitivity to be
, and set an upper limit on the branching ratio to
be at the 90% confidence level. This is a factor of 3.2
improvement compared to the previous results. The results of proceeding via parity-conservation were also presented in this paper
Experimental study of the decay
The first dedicated search for the rare neutral-kaon decay
has been carried out in the E391a experiment at the
KEK 12-GeV proton synchrotron. The final upper limit of 2.6 at
the 90% confidence level was set on the branching ratio for the decay.Comment: 23 pages, 27 figures, accepted for publication as a regular article
in Physical Review
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