1,125 research outputs found
Semiconductor-metal transition in semiconducting bilayer sheets of transition metal dichalcogenides
Using first-principles calculations we show that the band gap of bilayer
sheets of semiconducting transition metal dichalcogenides (TMDs) can be reduced
smoothly by applying vertical compressive pressure. These materials undergo a
universal reversible semiconductor to metal (S-M) transition at a critical
pressure. S-M transition is attributed to lifting the degeneracy of the bands
at fermi level caused by inter-layer interactions via charge transfer from
metal to chalcogens. The S-M transition can be reproduced even after
incorporating the band gap corrections using hybrid functionals and GW method.
The ability to tune the band gap of TMDs in a controlled fashion over a wide
range of energy, opens-up possibility for its usage in a range of applications.Comment: Accepted in Phys. Rev.
Quantum Kerr tunneling vacua on a -brane: An emergent Kerr black hole in five dimensions
We revisit a non-perturbative space-time curvature theory, underlying a two
form U(1) gauge dynamics, on a D4-brane. In particular, two different gauge
choices for a two form are explored underlying the dynamics of a geometric
torsion in a second order formalism. We obtain two non-extremal quantum Kerr
geometries in five dimensions on a pair of -brane in a type IIA
superstring theory. The quantum vacua are described by a vanishing torsion in a
gauge choice, underlying a geometric realization, on a non-BPS brane. It is
argued that the quantum Kerr vacua undergo tunneling and lead to a five
dimensional Kerr black hole in Einstein vacuum. A low energy limit in the
quantum Kerr vacua further re-assures an emergent Kerr black hole.Comment: 21 pages, 8 figure
Emergent Schwarzschild and Reissner-Nordstrom black holes in 4D: An effective curvature sourced by a B2-field on a D4-brane
We obtain a Schwarzschild and a Reissner-Nordstrom emergent black holes, by
exploring the torsion dynamics in a generalized curvature formulation,
underlying an effective D4-brane on S1. It is shown that a constant effective
metric, sourced by a background fluctuation in B2-potential, on a D3-brane
receives a dynamical quantum correction in presence of an electric charge.Comment: 7-pages, minor corrections, references added, to appear in Physical
Review
Quintessence and effective AdS brane geometries
A geometric torsion dynamics leading to an effective curvature in a second
order formalism on a D4-brane is revisited with a renewed interest. We obtain
two effective brane geometries on a vacuum created pair of -brane. One of them is shown to describe an AdS Schwarzschild spinning
black hole and the other is shown to describe a spinning black hole bound
state. It is argued that a D-instanton in a vacuum created anti D3-brane within
a pair may describe a quintessence. It may seen to incorporate a varying vacuum
energy density in a brane universe. We consider the effective curvature scalar
on to analyze torsion-less geometries on a vacuum created pair
of -brane. The emergent brane is shown to describe a
Schwarzschild and a Reissner-Nordstrom (RN) geometries in presence of extra
dimension(s).Comment: 20 pages, expanded discussion and added referenc
Emergent gravity/Non-linear U(1) gauge theory correspondence
Kaluza-Klein gravity is revisted, with renewed interest, in a type IIB string
theory on . The irreducible curvature tensors are worked out in
the, T-dual, emergent gravity in 4D to yield a non-linear U(1) gauge theory.
Interestingly, the T-duality may be seen to describe an open/closed string
duality at a self-dual string coupling. The obtained deformation in
black hole is analyzed to introduce the notion of temperature in the emergent
gravity underlying the recent idea of entropic force.Comment: 6 page
Strain-induced electronic phase transition and strong enhancement of thermopower of TiS2
Using first principles density functional theory calculations, we show a
semimetal to semiconducting electronic phase transition for bulk TiS 2 by
applying uniform biaxial tensile strain. This electronic phase transition is
triggered by charge transfer from Ti to S, which eventually reduces the overlap
between Ti-(d) and S-(p) orbitals. The electronic transport calculations show a
large anisotropy in electrical conductivity and thermopower, which is due to
the difference in the effective masses along the in-plane and out of plane
directions. Strain induced opening of band gap together with changes in
dispersion of bands lead to three-fold enhancement in thermopower for both p-
and n-type TiS2 . We further demonstrate that the uniform tensile strain, which
enhances the thermoelectric performance, can be achieved by doping TiS2 with
larger iso-electronic elements such as Zr or Hf at Ti sites.Comment: 8 pages, 6 figure
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