5,789 research outputs found

### Diffusion quantum Monte Carlo calculation of the quasiparticle effective mass of the two-dimensional homogeneous electron gas

The quasiparticle effective mass is a key quantity in the physics of electron
gases, describing the renormalization of the electron mass due to
electron-electron interactions. Two-dimensional electron gases are of
fundamental importance in semiconductor physics, and there have been numerous
experimental and theoretical attempts to determine the quasiparticle effective
mass in these systems. In this work we report quantum Monte Carlo results for
the quasiparticle effective mass of a two-dimensional homogeneous electron gas.
Our calculations differ from previous quantum Monte Carlo work in that much
smaller statistical error bars have been achieved, allowing for an improved
treatment of finite-size effects. In some cases we have also been able to use
larger system sizes than previous calculations

### Quantum Monte Carlo calculation of the energy band and quasiparticle effective mass of the two-dimensional Fermi fluid

We have used the diffusion quantum Monte Carlo method to calculate the energy
band of the two-dimensional homogeneous electron gas (HEG), and hence we have
obtained the quasiparticle effective mass and the occupied bandwidth. We find
that the effective mass in the paramagnetic HEG increases significantly when
the density is lowered, whereas it decreases in the fully ferromagnetic HEG.
Our calculations therefore support the conclusions of recent experimental
studies [Y.-W. Tan et al., Phys. Rev. Lett. 94, 016405 (2005); M. Padmanabhan
et al., Phys. Rev. Lett. 101, 026402 (2008); T. Gokmen et al., Phys. Rev. B 79,
195311 (2009)]. We compare our calculated effective masses with other
theoretical results and experimental measurements in the literature

### Quantum Monte Carlo study of the ground state of the two-dimensional Fermi fluid

We have used the variational and diffusion quantum Monte Carlo methods to
calculate the energy, pair correlation function, static structure factor, and
momentum density of the ground state of the two-dimensional homogeneous
electron gas. We have used highly accurate Slater-Jastrow-backflow trial wave
functions and twist averaging to reduce finite-size effects where applicable.
We compare our results with others in the literature and construct a
local-density-approximation exchange-correlation functional for 2D systems

### 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

### Quantum Monte Carlo Calculation of the Binding Energy of Bilayer Graphene

We report diffusion quantum Monte Carlo calculations of the interlayer
binding energy of bilayer graphene. We find the binding energies of the AA- and
AB-stacked structures at the equilibrium separation to be 11.5(9) and 17.7(9)
meV/atom, respectively. The out-of-plane zone-center optical phonon frequency
predicted by our binding-energy curve is consistent with available experimental
results. As well as assisting the modeling of interactions between graphene
layers, our results will facilitate the development of van der Waals
exchange-correlation functionals for density functional theory calculations.Comment: 5 pages and 3 figures, submitted to Phys. Rev. Lett.; supplemental
material is available on arXiv via the ancillary files attached to this
submissio

### 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

### Feshbach Resonance and Growth of a Bose-Einstein Condensate

Gross-Pitaevskii equation with gain is used to model Bose Einstein
condensation (BEC) fed by the surrounding thermal cloud. It is shown that the
number of atoms continuously injected into BEC from the reservoir can be
controlled by applying the external magnetic field via Feshbach resonance.Comment: 4 page

### Exciton and biexciton energies in bilayer systems

We report calculations of the energies of excitons and biexcitons in ideal
two-dimensional bilayer systems within the effective-mass approximation with
isotropic electron and hole masses. The exciton energies are obtained by a
simple numerical integration technique, while the biexciton energies are
obtained from diffusion quantum Monte Carlo calculations. The exciton binding
energy decays as the inverse of the separation of the layers, while the binding
energy of the biexciton with respect to dissociation into two separate excitons
decays exponentially

### A variance-minimization scheme for optimizing Jastrow factors

We describe a new scheme for optimizing many-electron trial wave functions by
minimizing the unreweighted variance of the energy using stochastic integration
and correlated-sampling techniques. The scheme is restricted to parameters that
are linear in the exponent of a Jastrow correlation factor, which are the most
important parameters in the wave functions we use. The scheme is highly
efficient and allows us to investigate the parameter space more closely than
has been possible before. We search for multiple minima of the variance in the
parameter space and compare the wave functions obtained using reweighted and
unreweighted variance minimization.Comment: 19 pages; 12 figure

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