94,106 research outputs found
Ab initio study of single molecular transistor modulated by gate-bias
We use a self-consistent method to study the current of the single molecular
transistor modulated by the transverse gate-bias in the level of the
first-principles calculations. The numerical results show that both the
polyacene-dithiol molecules and the fused-ring oligothiophene molecules are the
potential high-frequency molecular transistor controlled by the transverse
field. The long molecules of the polyacene-dithiol or the fused-ring thiophene
are in favor of realizing the gate-bias controlled molecular transistor. The
theoretical results suggest the related experiments.Comment: 14 pages, 7 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
Nambu-Goldstone Mechanism in Real-Time Thermal Field Theory
In a one-generation fermion condensate scheme of electroweak symmetry
breaking, it is proven based on Schwinger-Dyson equation in the real-time
thermal field theory in the fermion bubble diagram approximation that, at
finite temperature below the symmetry restoration temperature , a
massive Higgs boson and three massless Nambu-Goldstone bosons could emerge from
the spontaneous breaking of electroweak group
if the two fermion flavors in the one generation are mass-degenerate, thus
Goldstone Theorem is rigorously valid in this case. However, if the two fermion
flavors have unequal masses, owing to "thermal flactuation", the Goldstone
Theorem will be true only approximately for a very large momentum cut-off
in zero temperature fermion loop or for low energy scales. All
possible pinch singularities are proven to cancel each other, as is expected in
a real-time thermal field theory.Comment: 11 pages, revtex, no figure, Phys. Rev. D, to appea
Ground state fidelity in bond-alternative Ising chains with Dzyaloshinskii-Moriya interactions
A systematic analysis is performed for quantum phase transitions in a
bond-alternative one-dimensional Ising model with a Dzyaloshinskii-Moriya (DM)
interaction by using the fidelity of ground state wave functions based on the
infinite matrix product states algorithm. For an antiferromagnetic phase, the
fidelity per lattice site exhibits a bifurcation, which shows spontaneous
symmetry breaking in the system. A critical DM interaction is inversely
proportional to an alternating exchange coupling strength for a quantum phase
transition. Further, a finite-entanglement scaling of von Neumann entropy with
respect to truncation dimensions gives a central charge c = 0.5 at the critical
point.Comment: 6 pages, 4 figure
Broadband electromagnetic response and ultrafast dynamics of few-layer epitaxial graphene
We study the broadband optical conductivity and ultrafast carrier dynamics of
epitaxial graphene in the few-layer limit. Equilibrium spectra of nominally
buffer, monolayer, and multilayer graphene exhibit significant terahertz and
near-infrared absorption, consistent with a model of intra- and interband
transitions in a dense Dirac electron plasma. Non-equilibrium terahertz
transmission changes after photoexcitation are shown to be dominated by excess
hole carriers, with a 1.2-ps mono-exponential decay that reflects the
minority-carrier recombination time.Comment: 4 pages, 3 figures, final versio
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