782 research outputs found
Enhanced spin injection efficiency in a four-terminal double quantum dot system
Within the scheme of quantum rate equations, we investigate the spin-resolved
transport through a double quantum dot system with four ferromagnetic
terminals. It is found that the injection efficiency of spin-polarized
electrons can be significantly improved compared with single dot case. When the
magnetization in one of four ferromagnetic terminals is antiparallel with the
other three, the polarization rate of the current through one dot can be
greatly enhanced, accompanied by the drastic decrease of the current
polarization rate through the other one. The mechanism is the exchange
interaction between electrons in the two quantum dots, which can be a promising
candidate for the improvement of the spin injection efficiency.Comment: 10 pages and 5 figure
Production of single-charm hadrons by quark combination mechanism in -Pb collisions at TeV
If QGP-like medium is created in -Pb collisions at extremely high
collision energies, charm quarks that move in the medium can hadronize by
capturing the co-moving light quark(s) or anti-quark(s) to form the charm
hadrons. Using light quark spectra extracted from the experimental data
of light hadrons and a charm quark spectrum that is consistent with
perturbative QCD calculations, the central-rapidity data of spectra and
the spectrum ratios for mesons in the low range (
GeV) in minimum-bias -Pb collisions at TeV are well
described by quark combination mechanism in equal-velocity combination
approximation. The ratio in quark combination mechanism
exhibits the typical increase-peak-decrease behavior as the function of
, and the shape of the ratio for GeV is in agreement
with the preliminary data of ALICE collaboration in central rapidity region
and those of LHCb collaboration in forward rapidity region
. The global production of single-charm baryons is quantified using
the preliminary data and the possible enhancement (relative to light flavor
baryons) is discussed. The spectra of ,
in minimum-bias events and those of single-charm hadrons in high-multiplicity
event classes are predicted, which serves as the further test of the possible
change of the hadronization characteristic for low charm quarks in the
small system created in -Pb collisions at LHC energies.Comment: 13 pages, 8 figure
Selective attachment of benzonitrile on Si(111)-7×7: Configuration, selectivity, and mechanism
The cycloaddition of benzonitrile with Si(111)-7×7 has been investigated as a model system for understanding the interaction of conjugated π-electron systems with Si(111)-7×7 using high-resolution electron energy loss spectroscopy, x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy, scanning-tunneling microscopy (STM), and density-functional-theory calculation (perturbative Beck-Perdew functional in conjugation with a basis set of DN**). Vibrational features of chemisorbed benzonitrile unambiguously demonstrate that the cyano group directly interacts with Si surface dangling bonds, evidenced in the disappearance of C≡N stretching mode around 2256 cm-1 coupled with the appearance of C=N stretching mode at 1623 cm-1 and the retention of all vibrational signatures of phenyl ring. XPS shows that both C 1s and N 1s core levels of the cyano groups display large down-shifts by 2.5 and 1.5 eV, respectively, after chemisorption. A smaller down-shift of ∼0.8 eV is observed for the C 1s core level of phenyl group due to the weaker inductive effect of the formed C=N groups in chemisorbed benzonitrile than that of C≡N groups in physisorbed molecules. Compared with physisorbed molecules, the photoemission from πCN orbitals of chemisorbed benzonitrile is significantly reduced, suggesting the direct involvement of πCN in the surface binding. These experimental results show that the covalent attachment of benzonitrile on Si(111)-7×7 occurs in a selective manner through the (2+2) cycloaddition between the cyano group and the adjacent adatom-rest atom pair. The cycloadduct formed contains an intact phenyl ring protruding into vacuum, retaining aromaticity. This functionalized Si surface may serve as a substrate for further modification or act as an intermediate for fabrication of multilayer organic thin films or materials syntheses in vacuum
Checkerboard charge density wave and pseudogap in high- cuprates
We consider the scenario where a 4-lattice constant, rotationally symmetric
charge density wave (CDW) is present in the underdoped cuprates. We prove a
theorem that puts strong constraint on the possible form factor of such a CDW.
We demonstrate, within mean-field theory, that a particular form factor within
the allowed class describes the angle-resolved photoemission and scan tunneling
spectroscopy well. We conjecture that the ``large pseudogap'' in cuprates is
the consequence of this type of charge density wave.Comment: We add a new section II on the symmetry property of the checkerboard
CD
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