397 research outputs found
Electron-phonon bound state in graphene
The fine structure of the Dirac energy spectrum in graphene induced by
electron-optical phonon coupling is investigated in the portion of the spectrum
near the phonon emission threshold. The derived new dispersion equation in the
immediate neighborhood below the phonon threshold corresponds to an
electron-phonon bound state. We find that the singular vertex corrections
beyond perturbation theory increase strongly the electron-phonon binding
energy. The predicted enhancement of the effective electron-phonon coupling can
be measured using angle-resolved spectroscopy.Comment: 5 pages, 3 figure
Unconventional quasiparticle lifetime in undoped graphene
We address the question of how small can the quasiparticle decay rate be at
low energies in undoped graphene, where kinematical constraints are known to
prevent the decay into particle-hole excitations. For this purpose, we study
the renormalization of the phonon dispersion by many-body effects, which turns
out to be very strong in the case of the out-of-plane phonons at the K point of
the spectrum. We show that these evolve into a branch of very soft modes that
provide the relevant channel for quasiparticle decay, at energies below the
scale of the optical phonon modes. In this regime, we find that the decay rate
is proportional to the cube of the quasiparticle energy. This implies that a
crossover should be observed in transport properties from the linear dependence
characteristic of the high-energy regime to the much slower decay rate due to
the soft phonon modes.Comment: 5 pages, 1 figur
Helical liquid of snake states
We derive an exact solution to the problem of spin snake states induced in a
nonhomogeneous magnetic field by a combined action of the Rashba spin-orbit and
Zeeman fields. In an antisymmetric magnetic field the spin snake states are
nonlocal composite particles, originating from spatially separated entangled
spins. Adding an external homogeneous magnetic field breaks the spin-parity
symmetry gapping out the spectral branches, which results in a regular beating
pattern of the spin current. These new phenomena in a helical liquid of snake
states are proposed for an experimental realization.Comment: 5 pages, 3 figure
Electron-phonon bound states in graphene in a perpendicular magnetic field
The spectrum of electron-phonon complexes in a monolayer graphene is
investigated in the presence of a perpendicular quantizing magnetic field.
Despite the small electron-phonon coupling, usual perturbation theory is
inapplicable for calculation of the scattering amplitude near the threshold of
the optical phonon emission. Our findings beyond perturbation theory show that
the true spectrum near the phonon emission threshold is completely governed by
new branches, corresponding to bound states of an electron and an optical
phonon with a binding energy of the order of where
is the electron-phonon coupling and the phonon energy.Comment: To be published in Phys. Rev. Lett., 5 pages, 3 figures, 1 tabl
Plasmons in dimensionally mismatched Coulomb coupled graphene systems
We calculate the plasmon dispersion relation for Coulomb coupled metallic
armchair graphene nanoribbons and doped monolayer graphene. The crossing of the
plasmon curves, which occurs for uncoupled 1D and 2D systems, is split by the
interlayer Coulomb coupling into a lower and an upper plasmon branch. The upper
branch exhibits a highly unusual behavior with endpoints at finite .
Accordingly, the structure factor shows either a single or a double peak
behavior, depending on the plasmon wavelength. The new plasmon structure is
relevant to recent experiments, its properties can be controlled by varying the
system parameters, and be used in plasmonic applications.Comment: 5 pages, 3 figures; in press in Phys. Rev. Let
Beating of Friedel oscillations induced by spin-orbit interaction
By exploiting our recently derived exact formula for the Lindhard
polarization function in the presence of Bychkov-Rashba (BR) and Dresselhaus
(D) spin-orbit interaction (SOI), we show that the interplay of different SOI
mechanisms induces highly anisotropic modifications of the static dielectric
function. We find that under certain circumstances the polarization function
exhibits doubly-singular behavior, which leads to an intriguing novel
phenomenon, beating of Friedel oscillations. This effect is a general feature
of systems with BR+D SOI and should be observed in structures with a
sufficiently strong SOI.Comment: 3 figure
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