4,516 research outputs found
Universal symmetry-protected topological invariants for symmetry-protected topological states
Symmetry-protected topological (SPT) states are short-range entangled states
with a symmetry G. They belong to a new class of quantum states of matter which
are classified by the group cohomology in
d-dimensional space. In this paper, we propose a class of symmetry- protected
topological invariants that may allow us to fully characterize SPT states with
a symmetry group G (ie allow us to measure the cocycles in
that characterize the SPT states). We give
an explicit and detailed construction of symmetry-protected topological
invariants for 2+1D SPT states. Such a construction can be directly generalized
to other dimensions.Comment: 12 pages, 11 figures. Added reference
Quantized topological terms in weak-coupling gauge theories with symmetry and their connection to symmetry enriched topological phases
We study the quantized topological terms in a weak-coupling gauge theory with
gauge group and a global symmetry in space-time dimensions. We
show that the quantized topological terms are classified by a pair ,
where is an extension of by and an element in group
cohomology \cH^d(G,\R/\Z). When and/or when is finite, the
weak-coupling gauge theories with quantized topological terms describe gapped
symmetry enriched topological (SET) phases (i.e. gapped long-range entangled
phases with symmetry). Thus, those SET phases are classified by
\cH^d(G,\R/\Z), where . We also apply our theory to a simple case
, which leads to 12 different SET phases in 2+1D, where
quasiparticles have different patterns of fractional quantum numbers
and fractional statistics. If the weak-coupling gauge theories are gapless,
then the different quantized topological terms may describe different gapless
phases of the gauge theories with a symmetry , which may lead to different
fractionalizations of quantum numbers and different fractional statistics
(if in 2+1D).Comment: 13 pages, 2 figures, PRB accepted version with added clarification on
obtaining G_s charge for a given PSG with non-trivial topological terms.
arXiv admin note: text overlap with arXiv:1301.767
Broadband enhancement of light harvesting in luminescent solar concentrator
Luminescent solar concentrator (LSC) can absorb large-area incident sunlight,
then emit luminescence with high quantum efficiency, which finally be collected
by a small photovoltaic (PV) system. The light-harvesting area of the PV system
is much smaller than that of the LSC system, potentially improving the
efficiency and reducing the cost of solar cells. Here, based on Fermi-golden
rule, we present a theoretical description of the luminescent process in
nanoscale LSCs where the conventional ray-optics model is no longer applicable.
As an example calculated with this new model, we demonstrate that a slot
waveguide consisting of a nanometer-sized low-index slot region sandwiched by
two high-index regions provides a broadband enhancement of light harvesting by
the luminescent centers in the slot region. This is because the slot waveguide
can (1) greatly enhance the spontaneous emission due to the Purcell effect, (2)
dramatically increase the effective absorption cross-section of luminescent
centers, and (3) strongly improve the quantum efficiency of luminescent
centers. It is found that about 80% solar photons can be ultimately converted
to waveguide-coupled luminescent photons even for a low luminescent quantum
efficiency of 0.5. This LSC is potential to construct a tandem structure which
can absorb nearly full-spectrum solar photons, and also may be of special
interest for building integrated nano-PV applications
The Effects of Minimal Length, Maximal Momentum and Minimal Momentum in Entropic Force
In this paper, the modified entropic force law is studied by using a new kind
of generalized uncertainty principle which contains a minimal length, a minimal
momentum and a maximal momentum. Firstly, the quantum corrections to the
thermodynamics of a black hole is investigated. Then, according to Verlinde's
theory, the generalized uncertainty principle (GUP) corrected entropic force is
obtained. The result shows that the GUP corrected entropic force is related not
only to the properties of the black holes, but also to the Planck length and
the dimensionless constants and . Moreover,
based on the GUP corrected entropic force, we also derive the modified
Einstein's field equation (EFE) and the modified Friedmann equation.Comment: 16 pages. arXiv admin note: substantial text overlap with
arXiv:1604.0470
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