1,619 research outputs found
Formality of Sphere Bundles
We study the formality of orientable sphere bundles over connected compact
manifolds. When the base manifold is formal, we prove that the formality of the
bundle is equivalent to the vanishing of the Bianchi-Massey tensor introduced
by Crowley-Nordstr\"{o}m. As an example, this implies that the unit tangent
bundle over a formal manifold can only be formal when the base manifold has
vanishing Euler characteristic or a rational cohomology ring generated by one
element. When the base manifold is not formal, we give an obstruction for the
formality of sphere bundles whose Euler class is reducible.Comment: 18 page
Ab initio study of electron-phonon interaction in phosphorene
The monolayer of black phosphorous, or phosphorene, has recently emerged as a
new 2D semiconductor with intriguing highly anisotropic transport properties.
Existing calculations of its intrinsic phonon-limited electronic transport
properties so far rely on the deformation potential approximation, which is in
general not directly applicable to anisotropic materials since the deformation
along one specific direction can scatter electrons traveling in all directions.
We perform a first-principles calculation of the electron-phonon interaction in
phosphorene based on density functional perturbation theory and Wannier
interpolation. Our calculation reveals that 1) the high anisotropy provides
extra phase space for electron-phonon scattering, and 2) optical phonons have
appreciable contributions. Both effects cannot be captured by the deformation
potential calculations.Comment: 25 pages, 15 figure
Significant reduction of lattice thermal conductivity by electron-phonon interaction in silicon with high carrier concentrations: a first-principles study
Electron-phonon interaction has been well known to create major resistance to
electron transport in metals and semiconductors, whereas less studies were
directed to its effect on the phonon transport, especially in semiconductors.
We calculate the phonon lifetimes due to scattering with electrons (or holes),
combine them with the intrinsic lifetimes due to the anharmonic phonon-phonon
interaction, all from first-principles, and evaluate the effect of the
electron-phonon interaction on the lattice thermal conductivity of silicon.
Unexpectedly, we find a significant reduction of the lattice thermal
conductivity at room temperature as the carrier concentration goes above 1e19
cm-3 (the reduction reaches up to 45% in p-type silicon at around 1e21 cm-3), a
range of great technological relevance to thermoelectric materials.Comment: 19 pages, 5 figure
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