271 research outputs found
Direct observation of band-gap closure for a semiconducting carbon nanotube in a large parallel magnetic field
We have investigated the magnetoconductance of semiconducting carbon
nanotubes (CNTs) in pulsed, parallel magnetic fields up to 60 T, and report the
direct observation of the predicted band-gap closure and the reopening of the
gap under variation of the applied magnetic field. We also highlight the
important influence of mechanical strain on the magnetoconductance of the CNTs.Comment: 4 pages, 4 figure
Supercollision cooling in undoped graphene
Carrier mobility in solids is generally limited by electron-impurity or
electron-phonon scattering depending on the most frequently occurring event.
Three body collisions between carriers and both phonons and impurities are
rare; they are denoted supercollisions (SCs). Elusive in electronic transport
they should emerge in relaxation processes as they allow for large energy
transfers. As pointed out in Ref. \onlinecite{Song2012PRL}, this is the case in
undoped graphene where the small Fermi surface drastically restricts the
allowed phonon energy in ordinary collisions. Using electrical heating and
sensitive noise thermometry we report on SC-cooling in diffusive monolayer
graphene. At low carrier density and high phonon temperature the Joule power
obeys a law as a function of electronic temperature .
It overrules the linear law expected for ordinary collisions which has recently
been observed in resistivity measurements. The cubic law is characteristic of
SCs and departs from the dependence recently reported for metallic
graphene below the Bloch-Gr\"{u}neisen temperature. These supercollisions are
important for applications of graphene in bolometry and photo-detection
Stacking-order dependent transport properties of trilayer graphene
We report markedly different transport properties of ABA- and ABC-stacked
trilayer graphenes. Our experiments in double-gated trilayer devices provide
evidence that a perpendicular electric field opens an energy gap in the ABC
trilayer, while it causes the increase of a band overlap in the ABA trilayer.
In a perpendicular magnetic field, the ABA trilayer develops quantum Hall
plateaus at filling factors of \nu = 2, 4, 6... with a step of \Delta \nu = 2,
whereas the inversion symmetric ABC trilayer exhibits plateaus at \nu = 6 and
10 with 4-fold spin and valley degeneracy.Comment: 4 pages, 4 figure
Electric transport properties of single-walled carbon nanotubes functionalized by plasma ion irradiation method
科研費報告書収録論文(課題番号:13852016/研究代表者:畠山力三/プラズマイオン照射による新機能性進化ナノチューブ創製法の開発
Extended hadron and two-hadron operators of definite momentum for spectrum calculations in lattice QCD
Multi-hadron operators are crucial for reliably extracting the masses of
excited states lying above multi-hadron thresholds in lattice QCD Monte Carlo
calculations. The construction of multi-hadron operators with significant
coupling to the lowest-lying multi-hadron states of interest involves combining
single hadron operators of various momenta. The design and implementation of
large sets of spatially-extended single-hadron operators of definite momentum
and their combinations into two-hadron operators are described. The single
hadron operators are all assemblages of gauge-covariantly-displaced, smeared
quark fields. Group-theoretical projections onto the irreducible
representations of the symmetry group of a cubic spatial lattice are used in
all isospin channels. Tests of these operators on 24^3 x 128 and 32^3 x 256
anisotropic lattices using a stochastic method of treating the low-lying modes
of quark propagation which exploits Laplacian Heaviside quark-field smearing
are presented. The method provides reliable estimates of all needed
correlations, even those that are particularly difficult to compute, such as
eta eta -> eta eta in the scalar channel, which involves the subtraction of a
large vacuum expectation value. A new glueball operator is introduced, and the
evaluation of the mixing of this glueball operator with a quark-antiquark
operator, pi-pi, and eta-eta operators is shown to be feasible.Comment: 20 pages, 7 figures, 21 tables (final version accepted for
publication in Physical Review D
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