157 research outputs found

### Nonequilibrium charge dynamics of light-driven rings threaded by a magnetic flux

We study theoretically the charge polarization and the charge current
dynamics of a mesoscopic ring driven by short asymmetric electromagnetic pulses
and threaded by an external static magnetic flux. It is shown that the
pulse-induced charge polarization and the associated light-emission is
controllable by tuning the external magnetic flux. Applying two mutually
perpendicular pulses triggers a charge current in the ring. The interplay
between this nonequilibrium and the persistent currents is investigated and the
conditions under which the pulses stop the persistent current are identified.Comment: 6 pages, 2 figures; submitted to EP

### Pseudo-magnetic field distribution and pseudo-Landau levels in suspended graphene flakes

Combining the tight-binding approximation and linear elasticity theory for a
planar membrane, we investigate stretching of a graphene flake assuming that
two opposite edges of the sample are clamped by the contacts. We show that,
depending on the aspect ratio of the flake and its orientation, gapped states
may form in the membrane in the vicinity of the contacts. This gap in the
pre-contact region should be biggest for the armchair orientation of the flake
and width to length ratio of around 1.Comment: 7 pages + 3 figure

### Electrons and phonons in single layers of hexagonal indium chalcogenides from ab initio calculations

We use density functional theory to calculate the electronic band structures,
cohesive energies, phonon dispersions, and optical absorption spectra of
two-dimensional In$_2$X$_2$ crystals, where X is S, Se, or Te. We identify two
crystalline phases (alpha and beta) of monolayers of hexagonal In$_2$X$_2$, and
show that they are characterized by different sets of Raman-active phonon
modes. We find that these materials are indirect-band-gap semiconductors with a
sombrero-shaped dispersion of holes near the valence-band edge. The latter
feature results in a Lifshitz transition (a change in the Fermi-surface
topology of hole-doped In$_2$X$_2$) at hole concentrations $n_{\rm
S}=6.86\times 10^{13}$ cm$^{-2}$, $n_{\rm Se}=6.20\times 10^{13}$ cm$^{-2}$,
and $n_{\rm Te}=2.86\times 10^{13}$ cm$^{-2}$ for X=S, Se, and Te,
respectively, for alpha-In$_2$X$_2$ and $n_{\rm S}=8.32\times 10^{13}$
cm$^{-2}$, $n_{\rm Se}=6.00\times 10^{13}$ cm$^{-2}$, and $n_{\rm
Te}=8.14\times 10^{13}$ cm$^{-2}$ for beta-In$_2$X$_2$.Comment: 9 pages. arXiv admin note: text overlap with arXiv:1302.606

### Electrically Tunable Band Gap in Silicene

We report calculations of the electronic structure of silicene and the
stability of its weakly buckled honeycomb lattice in an external electric field
oriented perpendicular to the monolayer of Si atoms. We find that the electric
field produces a tunable band gap in the Dirac-type electronic spectrum, the
gap being suppressed by a factor of about eight by the high polarizability of
the system. At low electric fields, the interplay between this tunable band
gap, which is specific to electrons on a honeycomb lattice, and the Kane-Mele
spin-orbit coupling induces a transition from a topological to a band
insulator, whereas at much higher electric fields silicene becomes a semimetal

### Multifractality: generic property of eigenstates of 2D disordered metals.

The distribution function of local amplitudes of eigenstates of a
two-dimensional disordered metal is calculated. Although the distribution of
comparatively small amplitudes is governed by laws similar to those known from
the random matrix theory, its decay at larger amplitudes is non-universal and
much slower. This leads to the multifractal behavior of inverse participation
numbers at any disorder. From the formal point of view, the multifractality
originates from non-trivial saddle-point solutions of supersymmetric
$\sigma$-model used in calculations.Comment: 4 two-column pages, no figures, submitted to PRL

### Thermally excited spin-current in metals with embedded ferromagnetic nanoclusters

We show that a thermally excited spin-current naturally appears in metals
with embedded ferromagnetic nanoclusters. When such materials are subjected to
a magnetic field, a spin current can be generated by a temperature gradient
across the sample as a signature of electron-hole symmetry breaking in a metal
due to the electron spin-flip scattering from polarised magnetic moments. Such
a spin current can be observed via a giant magneto-thermopower which tracks the
polarisation state of the magnetic subsystem and is proportional to the
magnetoresistance. Our theory explains the recent experiment on Co clusters in
copper by S. Serrano-Guisan \textit{et al} [Nature Materials AOP,
doi:10.1038/nmat1713 (2006)

### Silicane and germanane: tight-binding and first-principles studies

We present a first-principles and tight-binding model study of silicane and
germanane, the hydrogenated derivatives of two-dimensional silicene and
germanene. We find that the materials are stable in freestanding form, analyse
the orbital composition, and derive a tight-binding model using
first-principles calculations to fit the parameters.Comment: Published in "2D Materials

### Landau levels in deformed bilayer graphene at low magnetic fields

We review the effect of uniaxial strain on the low-energy electronic
dispersion and Landau level structure of bilayer graphene. Based on the
tight-binding approach, we derive a strain-induced term in the low-energy
Hamiltonian and show how strain affects the low-energy electronic band
structure. Depending on the magnitude and direction of applied strain, we
identify three regimes of qualitatively different electronic dispersions. We
also show that in a weak magnetic field, sufficient strain results in the
filling factor ff=+-4 being the most stable in the quantum Hall effect
measurement, instead of ff=+-8 in unperturbed bilayer at a weak magnetic field.
To mention, in one of the strain regimes, the activation gap at ff=+-4 is, down
to very low fields, weakly dependent on the strength of the magnetic field.Comment: 14 single-column pages, 5 figures, more details on material presented
in arXiv:1104.502

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