1,469 research outputs found
Topological surface state under graphene for two-dimensional spintronics in air
Spin currents which allow for a dissipationless transport of information can
be generated by electric fields in semiconductor heterostructures in the
presence of a Rashba-type spin-orbit coupling. The largest Rashba effects occur
for electronic surface states of metals but these cannot exist but under
ultrahigh vacuum conditions. Here, we reveal a giant Rashba effect ({\alpha}_R
~ 1.5E-10 eVm) on a surface state of Ir(111). We demonstrate that its spin
splitting and spin polarization remain unaffected when Ir is covered with
graphene. The graphene protection is, in turn, sufficient for the spin-split
surface state to survive in ambient atmosphere. We discuss this result along
with evidences for a topological protection of the surface state.Comment: includes supplementary informatio
Feshbach shape resonance for high Tc superconductivity in superlattices of nanotubes
The case of a Feshbach shape resonance in the pairing mechanism for high T c
superconductivity in a crystalline lattice of doped metallic nanotubes is
described. The superlattice of doped metallic nanotubes provides a
superconductor with a strongly asymmetric gap. The disparity and different
spatial locations of the wave functions of electrons in different subbands at
the Fermi level should suppress the single electron impurity interband
scattering giving multiband superconductivity in the clean limit. The Feshbach
resonances will arise from the component single-particle wave functions out of
which the electron pair wave function is constructed: pairs of wave functions
which are time inverse of each other. The Feshbach shape resonance increases
the critical temperature by tuning the chemical potential at the Lifshitz
electronic topological transition (ETT) where the Fermi surface of one of the
bands changes from the one dimensional (1D) to the two dimensional (2D)
topology (1D/2D ETT).Comment: 6 pages, 4 figure
Polaron excitations in fullerenes: Theory as pi-conjugated systems
We review the recent theoretical treatment of fullerenes as pi-conjugated
systems. Polaronic properties due to the Jahn-Teller type effects are mainly
discussed. (1) A Su-Schrieffer-Heeger type electron-phonon model is applied to
fullerenes: C_60 and C_70, and is solved with the adiabatic approximation to
phonons. When the system (C_60 or C_70) is doped with one or two electrons (or
holes), the additional charges accumulate along almost an equatorial line of
the molecule. The dimerization becomes the weakest along the same line. Two
energy levels, the occupied state and the empty state, intrude largely in the
gap. The intrusion is larger in C_70 than in C_60. These are ``polarons'' in
doped fullerenes. It is also found that C_60 and C_70 are related mutually with
respect to electronical structures as well as lattice geometries. (2) We apply
the model to the fullerene epoxide C_60O. It has the polaron-type lattice
distortion around the oxygen, and also shows the energy level intrusion in the
gap. (3) Optical properties of C_60 are calculated and discussed. In the
absorption of the doped molecule, a new peak structure is present owing to the
polaronic distortion. In the luminescence of the neutral C_60, the spacing
between H_g(8)-phonon side-band peaks and the relative intensities agree well
with experiments. In the dispersion of the third harmonic generation, the
magnitudes of |chi^(3)| agree with those of experiments at the resonance of the
lowest allowed transition as well as in the region away from the resonance.Comment: Review article in Prog. Theor. Phys., 14pages, 7 figure
The topology of fullerenes
Fullerenes are carbon molecules that form polyhedral cages. Their bond structures are exactly the planar cubic graphs that have only pentagon and hexagon faces. Strikingly, a number of chemical properties of a fullerene can be derived from its graph structure. A rich mathematics of cubic planar graphs and fullerene graphs has grown since they were studied by Goldberg, Coxeter, and others in the early 20th century, and many mathematical properties of fullerenes have found simple and beautiful solutions. Yet many interesting chemical and mathematical problems in the field remain open. In this paper, we present a general overview of recent topological and graph theoretical developments in fullerene research over the past two decades, describing both solved and open problems. WIREs Comput Mol Sci 2015, 5:96–145. doi: 10.1002/wcms.1207 Conflict of interest: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website
The Influence of Electro-Mechanical Effects on Resonant Electron Tunneling Through Small Carbon Nano-Peapods
The influence of a fullerene molecule trapped inside a single-wall carbon
nanotube on resonant electron transport at low temperatures and strong
polaronic coupling is theoretically discussed. Strong peak to peak fluctuations
and anomalous temperature behavior of conductance amplitudes are predicted and
investigated. The influence of the chiral properties of carbon nanotubes on
transport is also studied.Comment: 17 pages, 3 figures. Replaced with published version. Important
changes. Open access: http://stacks.iop.org/1367-2630/10/04304
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