28 research outputs found
Observation of Quantum Capacitance of individual single walled carbon nanotubes
We report a measurement on quantum capacitance of individual semiconducting
and small band gap SWNTs. The observed quantum capacitance is remarkably
smaller than that originating from density of states and it implies a strong
electron correlation in SWNTs
Observation of Exciton-Phonon Sideband in Individual Metallic Single-Walled Carbon Nanotubes
Single-walled carbon nanotubes (SWCNTs) are quasi-one-dimensional systems
with poor Coulomb screening and enhanced electron-phonon interaction, and are
good candidates for excitons and exciton-phonon couplings in metallic state.
Here we report back scattering reflection experiments on individual metallic
SWCNTs. An exciton-phonon sideband separated by 0.19 eV from the first optical
transition peak is observed in a metallic SWCNT of chiral index (13,10), which
provides clear evidences of excitons in metallic SWCNTs. A static dielectric
constant of 10 is estimated from the reflectance spectrum.Comment: 5 pages, 3 figures; typos corrected, references updated, text
re-arrange
Low-Frequency Raman Modes and Electronic Excitations In Atomically Thin MoS2 Crystals
Atomically thin MoS crystals have been recognized as a quasi-2D
semiconductor with remarkable physics properties. This letter reports our Raman
scattering measurements on multilayer and monolayer MoS, especially in
the low-frequency range (50 cm). We find two low-frequency Raman
modes with contrasting thickness dependence. With increasing the number of
MoS layers, one shows a significant increase in frequency while the other
decreases following a 1/N (N denotes layer-number) trend. With the aid of
first-principle calculations we assign the former as the shear mode
and the latter as the compression vibrational mode. The opposite
evolution of the two modes with thickness demonstrates novel vibrational modes
in atomically thin crystal as well as a new and more precise way to
characterize thickness of atomically thin MoS films. In addition, we
observe a broad feature around 38 cm (~5 meV) which is visible only
under near-resonance excitation and pinned at the fixed energy independent of
thickness. We interpret the feature as an electronic Raman scattering
associated with the spin-orbit coupling induced splitting in conduction band at
K points in their Brillouin zone.Comment: 5 pages, 4 figure
Anomalously Robust Valley Polarization and Valley Coherence in Bilayer WS2
Coherence is a crucial requirement to realize quantum manipulation through
light-matter interactions. Here we report the observation of anomalously robust
valley polarization and valley coherence in bilayer WS2. The polarization of
the photoluminescence from bilayer WS2 inherits that of the excitation source
with both circularly and linearly polarized and retains even at room
temperature. The near unity circular polarization of the luminescence reveals
the coupling of spin, layer and valley degree of freedom in bilayer system,
while the linear polarized photoluminescence manifests quantum coherence
between the two inequivalent band extrema in momentum space, namely, the valley
quantum coherence in atomically thin bilayer WS2. This observation opens new
perspectives for quantum manipulation in atomically thin semiconductors
Distinct gut bacterial composition in Anoplophora glabripennis reared on two host plants
Anoplophora glabripennis (Coleoptera: Cerambycidae: Lamiinae) is an invasive wood borer pest that has caused considerable damage to forests. Gut bacteria are of great importance in the biology and ecology of herbivores, especially in growth and adaptation; however, change in the gut bacterial community of this pest feeding on different hosts is largely unknown. In this study, we investigated the gut bacterial communities of A. glabripennis larvae fed on different preferred hosts, Salix matsudana and Ulmus pumila, using 16S rDNA high-throughput sequencing technology. A total of 15 phyla, 25 classes, 65 orders, 114 families, 188 genera, and 170 species were annotated in the gut of A. glabripennis larvae fed on S. matsudana or U. pumila using a 97% similarity cutoff level. The dominant phyla were Firmicutes and Proteobacteria and the core dominant genera were Enterococcus, Gibbsiella, Citrobacter, Enterobacter, and Klebsiella. There was significantly higher alpha diversity in the U. pumila group than in the S. matsudana group, and principal co-ordinate analysis showed significant differences in gut bacterial communities between the two groups. The genera with significant abundance differences between the two groups were Gibbsiella, Enterobacter, Leuconostoc, Rhodobacter, TM7a, norank, Rhodobacter, and Aurantisolimonas, indicating that the abundance of larval gut bacteria was affected by feeding on different hosts. Further network diagrams showed that the complexity of the network structure and the modularity were higher in the U. pumila group than in the S. matsudana group, suggesting more diverse gut bacteria in the U. pumila group. The dominant role of most gut microbiota was related to fermentation and chemoheterotrophy, and specific OTUs positively correlated with different functions were reported. Our study provides an essential resource for the gut bacteria functional study of A. glabripennis associated with host diet