10 research outputs found
Sondeo arqueológico Cueva Pintada, detalle carbón [Material gráfico]
Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201
Spectrum of exciton states in monolayer transition metal dichalcogenides : angular momentum and Landau levels
A four-band exciton Hamiltonian is constructed starting from the
single-particle Dirac Hamiltonian for charge carriers in monolayer transition
metal dichalcogenides (TMDs). The angular part of the exciton wave function can
be separated from the radial part, in the case of zero center of mass momentum
excitons, by exploiting the eigenstates of the total exciton angular momentum
operator with which the Hamiltonian commutes. We explain why this approach
fails for excitons with finite center of mass momentum or in the presence of a
perpendicular magnetic field and present an approximation to resolve this
issue. We calculate the (binding) energy and average interparticle distance of
different excited exciton states in different TMDs and compare these with
results available in the literature. Remarkably, we find that the intervalley
exciton ground state in the valley has angular momentum , which
is due to the pseudospin of the separate particles. The exciton mass and the
exciton Landau levels are calculated and we find that the degeneracy of exciton
states with opposite relative angular momentum is altered by a magnetic field.Comment: 10 pages, 5 figures, 3 table
Interlayer excitons in transition metal dichalcogenide heterostructures
Starting from the single-particle Dirac Hamiltonian for charge carriers in
monolayer transition metal dichalcogenides (TMDs), we construct a four-band
Hamiltonian describing interlayer excitons consisting of an electron in one TMD
layer and a hole in the other TMD layer. An expression for the electron-hole
interaction potential is derived, taking into account the effect of the
dielectric environment above, below, and between the two TMD layers as well as
polarization effects in the transition metal layer and in the chalcogen layers
of the TMD layers. We calculate the interlayer exciton binding energy and
average in-plane interparticle distance for different TMD heterostructures. The
effect of different dielectric environments on the exciton binding energy is
investigated and a remarkable dependence on the dielectric constant of the
barrier between the two layers is found, resulting from competing effects as a
function of the in-plane and out-of-plane dielectric constants of the barrier.
The polarization effects in the chalcogen layers, which in general reduce the
exciton binding energy, can lead to an increase in binding energy in the
presence of strong substrate effects by screening the substrate. The excitonic
absorbance spectrum is calculated and we show that the interlayer exciton peak
depends linearly on a perpendicular electric field, which agrees with recent
experimental results.Comment: 11 pages, 7 figures, 5 table
Reply to "Comment on `Excitons, trions, and biexcitons in transition-metal dichalcogenides: Magnetic-field dependence'"
Virtual LEGO Modelling on Multi-Touch Surfaces
Construction of LEGO models is a popular hobby, not only among children and young teenagers, but also for adults of all ages.
Following the technological evolution and the integration of computers into the everyday life, several applications for virtual
LEGO modelling have been created. However, these applications generally have interfaces based on windows, icons, menus
and pointing devices, the so-called WIMP interfaces, thus being unnatural and hard-to-use for many users. Taking advantage
of new trends in of interaction paradigms we developed an innovative solution for virtual LEGO modelling using a horizontal
multi-touch surface. To achieve better results, we selected the most common virtual LEGO applications and performed a
comparative study, identifying advantages and disadvantages of each one. In this paper we briefly present that study and describe the application developed upon it
Magnetopolaron effect on shallow-impurity states in the presence of magnetic and intense terahertz laser fields in the Faraday configuration
Doping-dependent switch from one- to two-component superfluidity in coupled electron-hole van der Waals heterostructures
Graphene quantum blisters : a tunable system to confine charge carriers
Due to Klein tunneling, electrostatic confinement of electrons in graphene is
not possible. This hinders the use of graphene for quantum dot applications.
Only through quasi-bound states with finite lifetime has one achieved to
confine charge carriers. Here we propose that bilayer graphene with a local
region of decoupled graphene layers is able to generate bound states under the
application of an electrostatic gate. The discrete energy levels in such a
quantum blister correspond to localized electron and hole states in the top and
bottom layers. We find that this layer localization and the energy spectrum
itself are tunable by a global electrostatic gate and that the latter also
coincides with the electronic modes in a graphene disk. Curiously, states with
energy close to the continuum exist primarily in the classically forbidden
region outside the domain defining the blister. The results are robust against
variations in size and shape of the blister which shows that it is a versatile
system to achieve tunable electrostatic confinement in graphene.Comment: 6 pages, 4 figure