15,467 research outputs found
Study of the weak annihilation contributions in charmless decays
In this paper, in order to probe the spectator-scattering and weak
annihilation contributions in charmless (where stands for a
light vector meson) decays, we perform the -analyses for the end-point
parameters within the QCD factorization framework, under the constraints from
the measured , , and
decays. The fitted results indicate that the end-point
parameters in the factorizable and nonfactorizable annihilation topologies are
non-universal, which is also favored by the charmless and (where
stands for a light pseudo-scalar meson) decays observed in the previous
work. Moreover, the abnormal polarization fractions measured by the LHCb
collaboration can be reconciled through the weak annihilation corrections.
However, the branching ratio of decay exhibits a
tension between the data and theoretical result, which dominates the
contributions to in the fits. Using the fitted end-point
parameters, we update the theoretical results for the charmless
decays, which will be further tested by the LHCb and Belle-II experiments in
the near future.Comment: 31 pages, 4 figures, 6 table
Flat-band and multi-dimensional fermions in Pb10(PO4)6O4
Employing a combination of first-principles calculations and low-energy
effective models, we present a comprehensive investigation on the electronic
structure of Pb(PO)O, which exhibits remarkable
quasi-one-dimensional flat-band around the Fermi level that contains novel
multi-dimensional fermions. These flat bands predominantly originate from
orbital of the oxygen molecules chain at Wyckoff positions, and
thus can be well-captured by a four-band tight-binding model. Furthermore, the
abundant crystal symmetry inherent to Pb(PO)O provides
an ideal platform for the emergence of various multi-dimensional fermions,
including a 0D four-fold degenerated Dirac fermion with quadratic dispersion, a
1D quadratic/linear nodal-line (QNL/LNL) fermion along symmetric -paths, 1D
hourglass nodal-line (HNL) fermion linked to the Dirac fermion, and a 2D
symmetry-enforced nodal surface (NS) found on the = plane. Moreover,
when considering the weak ferromagnetic order, Pb(PO)O
transforms into a rare semi-half-metal, which is characterized by the presence
of Dirac fermion and HNL fermion at the Fermi level for a single spin channel
exhibiting 100 spin polarization. Our findings reveal the coexistence of
flat bands, diverse topological semimetal states and ferromagnetism within in
Pb(PO)O, which may provide valuable insights for
further exploring intriguing interplay between superconductivity and exotic
electronic states.Comment: 8 pages, 4 figure
Improving thermoelectric properties of p-type Bi2Te3-based alloys by spark plasma sintering
AbstractHigh-performance (Bi2Te3)x(Sb2Te3)1βx bulk materials were prepared by combining fusion technique with spark plasma sintering, and their thermoelectric properties were investigated. The electrical resistivity and Seebeck coefficient increase greatly and the thermal conductivity decreases significantly with the increase of Bi2Te3 content, which leads to a great improvement in the thermoelectric figure of merit ZT. The maximum ZT value reaches 1.33 at 398 K for the composition of 20%Bi2Te3-80%Sb2Te3 with 3% (mass fraction) excess Te
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