3,635 research outputs found
Abelianization of BPS Quivers and the Refined Higgs Index
We count Higgs "phase" BPS states of general non-Abelian quiver, possibly
with loops, by mapping the problem to its Abelian, or toric, counterpart and
imposing Weyl invariance later. Precise Higgs index computation is particularly
important for quivers with superpotentials; the Coulomb "phase" index is
recently shown to miss important BPS states, dubbed intrinsic Higgs states or
quiver invariants. We demonstrate how the refined Higgs index is naturally
decomposed to a sum over partitions of the charge. We conjecture, and show in
simple cases, that this decomposition expresses the Higgs index as a sum over a
set of partition-induced Abelian quivers of the same total charge but
generically of smaller rank. Unlike the previous approach inspired by a similar
decomposition of the Coulomb index, our formulae compute the quiver invariants
directly, and thus offer a self-complete routine for counting BPS states.Comment: 38 pages, 13 figure
Time-resolved photoluminescence of the size-controlled ZnO nanorods
Size dependence of the time-resolved photoluminescence (TRPL) has been investigated for the ZnO nanorods fabricated by catalyst-free metalorganic chemical vapor deposition. The nanorods have a diameter of 35 nm and lengths in the range of 150 nm to 1.1 mum. The TRPL decay rate decreases monotonically as the length of the nanorods increases in the range of 150 to 600 nm. Decrease of the radiative decay rate of the exciton-polariton has been invoked to account for the results. (C) 2003 American Institute of Physics.X11100sciescopu
Photoluminescent characteristics of Ni-catalyzed GaN nanowires
The authors report on time-integrated and time-resolved photoluminescence (PL) of GaN nanowires grown by the Ni-catalyst-assisted vapor-liquid-solid method. From PL spectra of Ni-catalyzed GaN nanowires at 10 K, several PL peaks were observed at 3.472, 3.437, and 3.266 eV, respectively. PL peaks at 3.472 and 3.266 eV are attributed to neutral-donor-bound excitons and donor-acceptor pair, respectively. Furthermore, according to the results from temperature-dependent and time-resolved PL measurements, the origin of the PL peak at 3.437 eV is also discussed. (c) 2006 American Institute of Physics.X1147sciescopu
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