71 research outputs found
Direct observation of split-mode exciton-polaritons in a single MoS nanotube
A single nanotube synthesized from a transition metal dichalcogenide (TMDC)
exhibits strong exciton resonances and, in addition, can support optical
whispering gallery modes. This combination is promising for observing
exciton-polaritons without an external cavity. However, traditional
energy-momentum-resolved detection methods are unsuitable for this tiny object.
Instead, we propose to use split optical modes in a twisted nanotube with the
flattened cross-section, where a gradually decreasing gap between the opposite
walls leads to a change in mode energy, similar to the effect of the barrier
width on the eigenenergies in the double-well potential. Using
micro-reflectance spectroscopy, we investigated the rich pattern of polariton
branches in single MoS tubes with both variable and constant gaps. Observed
Rabi splitting in the 40 - 60 meV range is comparable to that for a MoS
monolayer in a microcavity. Our results, based on the polariton dispersion
measurements and polariton dynamics analysis, present a single TMDC nanotube as
a perfect polaritonic structure for nanophotonics
Twisted Nanotubes of Transition Metal Dichalcogenides with Split Optical Modes for Tunable Radiated Light Resonators
Synthesized micro- and nanotubes composed of transition metal dichalcogenides
(TMDCs) such as MoS are promising for many applications in nanophotonics,
because they combine the abilities to emit strong exciton luminescence and to
act as whispering gallery microcavities even at room temperature. In addition
to tubes in the form of hollow cylinders, there is an insufficiently-studied
class of twisted tubes, the flattened cross section of which rotates along the
tube axis. As shown by theoretical analysis, in such nanotubes the interaction
of electromagnetic waves excited at opposite sides of the cross section can
cause splitting of the whispering gallery modes. By studying
micro-photoluminescence spectra measured along individual MoS tubes, it has
been established that the splitting value, which controls the energies of the
split modes, depends exponentially on the aspect ratio of the cross section,
which varies in "breathing" tubes, while the relative intensity of the modes in
a pair is determined by the angle of rotation of the cross section. These
results open up the possibility of creating multifunctional tubular TMDC
nanodevices that provide resonant amplification of self-emitting light at
adjustable frequencies
Pan-cancer analysis of whole genomes identifies driver rearrangements promoted by LINE-1 retrotransposition
About half of all cancers have somatic integrations of retrotransposons. Here, to characterize their role in oncogenesis, we analyzed the patterns and mechanisms of somatic retrotransposition in 2,954 cancer genomes from 38 histological cancer subtypes within the framework of the Pan-Cancer Analysis of Whole Genomes (PCAWG) project. We identified 19,166 somatically acquired retrotransposition events, which affected 35% of samples and spanned a range of event types. Long interspersed nuclear element (LINE-1; L1 hereafter) insertions emerged as the first most frequent type of somatic structural variation in esophageal adenocarcinoma, and the second most frequent in head-and-neck and colorectal cancers. Aberrant L1 integrations can delete megabase-scale regions of a chromosome, which sometimes leads to the removal of tumor-suppressor genes, and can induce complex translocations and large-scale duplications. Somatic retrotranspositions can also initiate breakage–fusion–bridge cycles, leading to high-level amplification of oncogenes. These observations illuminate a relevant role of L1 retrotransposition in remodeling the cancer genome, with potential implications for the development of human tumors
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