77 research outputs found
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
Auger recombination of dark excitons in and monolayers
We propose a novel phonon assisted Auger process unique to the electronic
band structure of monolayer transition metal dichalcogenides (TMDCs), which
dominates the radiative recombination of ground state excitons in Tungsten
based TMDCs. Using experimental and DFT computed values for the exciton
energies, spin-orbit splittings, optical matrix element, and the Auger matrix
elements, we find that the Auger process begins to dominate at carrier
densities as low as , thus providing a plausible
explanation for the low quantum efficiencies reported for these materials.Comment: 5 pages, 2 figure
Hybrid -tight-binding model for intersubband optics in atomically thin InSe films
We propose atomic films of n-doped -InSe as a platform for
intersubband optics in the infrared (IR) and far infrared (FIR) range, coupled
to out-of-plane polarized light. Depending on the film thickness (number of
layers) of the InSe film these transitions span from eV for bilayer
to eV for 15-layer InSe. We use a hybrid theory and tight-binding model, fully parametrized using density
functional theory, to predict their oscillator strengths and thermal linewidths
at room temperature
Stacking domains and dislocation networks in marginally twisted bilayers of transition metal dichalcogenides
We apply a multiscale modeling approach to study lattice reconstruction in
marginally twisted bilayers of transition metal dichalcogenides (TMD). For
this, we develop DFT-parametrized interpolation formulae for interlayer
adhesion energies of MoSe, WSe, MoS, and WS, combine those with
elasticity theory, and analyze the bilayer lattice relaxation into mesoscale
domain structures. Paying particular attention to the inversion asymmetry of
TMD monolayers, we show that 3R and 2H stacking domains, separated by a network
of dislocations develop for twist angles and for,
respectively, bilayers with parallel (P) and antiparallel (AP) orientation of
the monolayer unit cells and suggest how the domain structures would manifest
itself in local probe scanning of marginally twisted P- and AP-bilayers
Tunable Berry curvature, valley and spin Hall effect in Bilayer MoS
The chirality of electronic Bloch bands is responsible for many intriguing
properties of layered two-dimensional materials. We show that in bilayers of
transition metal dichalcogenides (TMDCs), unlike in few-layer graphene and
monolayer TMDCs, both intra-layer and inter-layer couplings give important
contributions to the Berry-curvature in the and valleys of the
Brillouin zone. The inter-layer contribution leads to the stacking dependence
of the Berry curvature and we point out the differences between the commonly
available 3R type and 2H type bilayers. Due to the inter-layer contribution the
Berry curvature becomes highly tunable in double gated devices. We study the
dependence of the valley Hall and spin Hall effects on the stacking type and
external electric field. Although the valley and spin Hall conductivities are
not quantized, in MoS 2H bilayers they may change sign as a function of the
external electric field which is reminiscent of the behaviour of lattice Chern
insulators.Comment: 19 pages, 6 figure
Crossover from weakly indirect to direct excitons in atomically thin films of InSe
We perform a theory analysis of the spectra of the
lowest energy and excited states of the excitons in few-layer atomically thin
films of InSe taking into account in-plane electric polarizability of the film
and the influence of the encapsulation environment. For the thinner films, the
lowest-energy state of the exciton is weakly indirect in momentum space, with
its dispersion showing minima at a layer-number-dependent wave number, due to
an inverted edge of a relatively flat topmost valence band branch of the InSe
film spectrum and we compute the activation energy from the momentum dark
exciton ground state into the bright state. For the films with more than seven
InSe layers, the exciton dispersion minimum shifts to -point.Comment: 12 pages, 7 figure
Electron spin resonance signal of Luttinger liquids and single-wall carbon nanotubes
A comprehensive theory of electron spin resonance (ESR) for a Luttinger
liquid (LL) state of correlated metals is presented. The ESR measurables such
as the signal intensity and the line-width are calculated in the framework of
Luttinger liquid theory with broken spin rotational symmetry as a function of
magnetic field and temperature. We obtain a significant temperature dependent
homogeneous line-broadening which is related to the spin symmetry breaking and
the electron-electron interaction. The result crosses over smoothly to the ESR
of itinerant electrons in the non-interacting limit. These findings explain the
absence of the long-sought ESR signal of itinerant electrons in single-wall
carbon nanotubes when considering realistic experimental conditions.Comment: 5 pages, 1 figur
Multifaceted moir\'e superlattice physics in twisted WSe bilayers
Lattice reconstruction in twisted transition-metal dichalcogenide (TMD)
bilayers gives rise to piezo- and ferroelectric moir\'e potentials for
electrons and holes, as well as a modulation of the hybridisation across the
bilayer. Here, we develop hybrid tight-binding
models to describe electrons and holes in the relevant valleys of twisted TMD
homobilayers with parallel (P) and anti-parallel (AP) orientations of the
monolayer unit cells. We apply these models to describe moir\'e superlattice
effects in twisted WSe bilayers, in conjunction with microscopic \emph{ab
initio} calculations, and considering the influence of encapsulation, pressure
and an electric displacement field. Our analysis takes into account mesoscale
lattice relaxation, interlayer hybridisation, piezopotentials, and a weak
ferroelectric charge transfer between the layers, and describes a multitude of
possibilities offered by this system, depending on the choices of P or AP
orientation, twist angle magnitude, and electron/hole valley.Comment: 44 pages, 27 figures, 6 appendices. For v2: Modelling and analysis
for Q-point bands and minibands adde
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