6,679 research outputs found
Interaction-induced topological properties of two bosons in flat-band systems
In flat-band systems, destructive interference leads to the localization of
non-interacting particles and forbids their motion through the lattice.
However, in the presence of interactions the overlap between neighbouring
single-particle localized eigenstates may enable the propagation of bound pairs
of particles. In this work, we show how these interaction-induced hoppings can
be tuned to obtain a variety of two-body topological states. In particular, we
consider two interacting bosons loaded into the orbital angular momentum
states of a diamond-chain lattice, wherein an effective flux may yield a
completely flat single-particle energy landscape. In the weakly-interacting
limit, we derive effective single-particle models for the two-boson
quasiparticles which provide an intuitive picture of how the topological states
arise. By means of exact diagonalization calculations, we benchmark these
states and we show that they are also present for strong interactions and away
from the strict flat-band limit. Furthermore, we identify a set of doubly
localized two-boson flat-band states that give rise to a special instance of
Aharonov-Bohm cages for arbitrary interactions
Identification of fullerene-like CdSe nanoparticles from optical spectroscopy calculations
Semiconducting nanoparticles are the building blocks of optical nanodevices
as their electronic states, and therefore light absorption and emission, can be
controlled by modifying their size and shape. CdSe is perhaps the most studied
of these nanoparticles, due to the efficiency of its synthesis, the high
quality of the resulting samples, and the fact that the optical gap is in the
visible range. In this article, we study light absorption of CdSe
nanostructures with sizes up to 1.5 nm within density functional theory. We
study both bulk fragments with wurtzite symmetry and novel fullerene-like
core-cage structures. The comparison with recent experimental optical spectra
allows us to confirm the synthesis of these fullerene-like CdSe clusters
Mode-coupling and the pygmy dipole resonance in a relativistic two-phonon model
A two-phonon version of the relativistic quasiparticle time blocking
approximation (RQTBA-2) represents a new class of many-body models for nuclear
structure calculations based on the covariant energy density functional. As a
fully consistent extension of the relativistic quasiparticle random phase
approximation (RQRPA), the two-phonon RQTBA implies a fragmentation of nuclear
states over two-quasiparticle and two-phonon configurations. This leads, in
particular, to a splitting-out of the lowest 1 state as a member of the
two-phonon quintuplet from the RQRPA pygmy dipole mode, thus
establishing a physical mixing between these three modes. The inclusion of the
two-phonon configurations in the model space allows to describe the positions
and the reduced transition probabilities of the lowest 1 states in isotopes
Sn as well as the low-energy fraction of the dipole strength
without any adjustment procedures. The model is also applied to the low-lying
dipole strength in neutron-rich Ni isotopes. Recent experimental
data for Ni are reproduced fairly well
Spin filtering in nanowire directional coupler
The spin transport characteristics of a nanowire directional electronic
coupler have been evaluated theoretically via a transfer matrix approach. The
application of a gate field in the region of mixing allows for control of spin
current through the different leads of the coupler via the Rashba spin-orbit
interaction. The combination of spin-orbit interaction and applied gate
voltages on different legs of the coupler give rise to a controllable
modulation of the spin polarization. Both structural factors and field strength
tuning lead to a rich phenomenology that could be exploited in spintronic
devices.Comment: 9 pages, 4 figure
On a generalized gravitational Aharonov-Bohm effect
A massless spinor particle is considered in the background gravitational
field due to a rotating body. In the weak field approximation it is shown that
the solution of the Weyl equations depend on the angular momentum of the
rotating body, which does not affect the curvature in this approximation. This
result may be looked upon as a generalization of the gravitational
Aharonov-Bohm effect.Comment: 10 pages, LATEX fil
Frustrated multiband superconductivity
We show that a clean multiband superconductor may display one or several
phase transitions with increasing temperature from or to frustrated
configurations of the relative phases of the superconducting order parameters.
These transitions may occur when more than two bands are involved in the
formation of the superconducting phase and when the number of repulsive
interband interactions is odd. These transitions are signalled by slope changes
in the temperature dependence of the superconducting gaps.Comment: 5 pages, 3 figure
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