231 research outputs found
Direct photoluminescence probing of ferromagnetism in monolayer two-dimensional CrBr3
Atomically thin magnets are the key element to build up spintronics based on
two-dimensional materials. The surface nature of two-dimensional ferromagnet
opens up opportunities to improve the device performance efficiently. Here, we
report the intrinsic ferromagnetism in atomically thin monolayer CrBr3,
directly probed by polarization resolved magneto-photoluminescence. The
spontaneous magnetization persists in monolayer CrBr3 with a Curie temperature
of 34 K. The development of magnons by the thermal excitation is in line with
the spin-wave theory. We attribute the layer-number dependent hysteresis loops
in thick layers to the magnetic domain structures. As a stable monolayer
material in air, CrBr3 provides a convenient platform for fundamental physics
and pushes the potential applications of the two-dimensional ferromagnetism.Comment: 27 pages, 10 figure
Valley-Layer Coupling: A New Design Principle for Valleytronics
We introduce the concept of valley-layer coupling (VLC) in two-dimensional
materials, where the low-energy electronic states in the emergent valleys have
valley-contrasted layer polarization such that each state is spatially
localized on the top or bottom super-layer. The VLC enables a direct coupling
between valley and gate electric field, opening a new route towards
electrically controlled valleytronics. We analyze the symmetry requirements for
the system to host VLC, demonstrate our idea via first-principles calculations
and model analysis of a concrete 2D material example, and show that an
electric, continuous, wide-range, and switchable control of valley polarization
can be achieved by VLC. Furthermore, we find that systems with VLC can exhibit
other interesting physics, such as valley-contrasting linear dichroism and
optical selection of the electric polarization of interlayer excitons.Comment: 6 pages, 4 figure
Genome Structure Drives Patterns of Gene Family Evolution in Ciliates, a Case Study Using \u3ci\u3eChilodonella uncinata\u3c/i\u3e (Protista, Ciliophora, Phyllopharyngea)
In most lineages, diversity among gene family members results from gene duplication followed by sequence divergence. Because of the genome rearrangements during the development of somatic nuclei, gene family evolution in ciliates involves more complex processes. Previous work on the ciliate Chilodonella uncinata revealed that macronuclear β-tubulin gene family members are generated by alternative processing, in which germline regions are alternatively used in multiple macronuclear chromosomes. To further study genome evolution in this ciliate, we analyzed its transcriptome and found that (1) alternative processing is extensive among gene families; and (2) such gene families are likely to be C. uncinata specific. We characterized additional macronuclear and micronuclear copies of one candidate alternatively processed gene family-a protein kinase domain containing protein (PKc)-from two C. uncinata strains. Analysis of the PKc sequences reveals that (1) multiple PKc gene family members in the macronucleus share some identical regions flanked by divergent regions; and (2) the shared identical regions are processed from a single micronuclear chromosome. We discuss analogous processes in lineages across the eukaryotic tree of life to provide further insights on the impact of genome structure on gene family evolution in eukaryotes
Bright room temperature single photon source at telecom range in cubic silicon carbide
Single photon emitters (SPEs) play an important role in a number of quantum
information tasks such as quantum key distributions. In these protocols,
telecom wavelength photons are desired due to their low transmission loss in
optical fibers. In this paper, we present a study of bright single-photon
emitters in cubic silicon carbide (3C-SiC) emitting in the telecom range. We
find that these emitters are photostable and bright at room temperature with a
count rate of ~ MHz. Together with the fact that SiC is a growth and
fabrication-friendly material, our result may pave the way for its future
application in quantum communication technology applications.Comment: Accepted by Nature Communication
High-efficiency generation of nanoscale single silicon vacancy defect array in silicon carbide
Color centers in silicon carbide have increasingly attracted attention in
recent years owing to their excellent properties such as single photon
emission, good photostability, and long spin coherence time even at room
temperature. As compared to diamond which is widely used for holding
Nitrogen-vacancy centers, SiC has the advantage in terms of large-scale,
high-quality and low cost growth, as well as advanced fabrication technique in
optoelectronics, leading to the prospects for large scale quantum engineering.
In this paper, we report experimental demonstration of the generation of
nanoscale single defect array through ion implantation without the
need of annealing. defects are generated in pre-determined locations
with resolution of tens of nanometers. This can help in integrating
defects with the photonic structures which, in turn, can improve the emission
and collection efficiency of defects when it is used in spin photonic
quantum network. On the other hand, the defects are shallow and they are
generated below the surface which can serve as critical resources
in quantum sensing application
Genome Analyses of the New Model Protist \u3ci\u3eEuplotes vannus\u3c/i\u3e Focusing on Genome Rearrangement and Resistance to Environmental Stressors
As a model organism for studies of cell and environmental biology, the free-living and cosmopolitan ciliate Euplotes vannus shows intriguing features like dual genome architecture (i.e., separate germline and somatic nuclei in each cell/organism), “gene-sized” chromosomes, stop codon reassignment, programmed ribosomal frameshifting (PRF) and strong resistance to environmental stressors. However, the molecular mechanisms that account for these remarkable traits remain largely unknown. Here we report a combined analysis of de novo assembled high-quality macronuclear (MAC; i.e., somatic) and partial micronuclear (MIC; i.e., germline) genome sequences for E. vannus, and transcriptome profiling data under varying conditions. The results demonstrate that: (a) the MAC genome contains more than 25,000 complete “gene-sized” nanochromosomes (~85 Mb haploid genome size) with the N50 ~2.7 kb; (b) although there is a high frequency of frameshifting at stop codons UAA and UAG, we did not observe impaired transcript abundance as a result of PRF in this species as has been reported for other euplotids; (c) the sequence motif 5′-TA-3′ is conserved at nearly all internally-eliminated sequence (IES) boundaries in the MIC genome, and chromosome breakage sites (CBSs) are duplicated and retained in the MAC genome; (d) by profiling the weighted correlation network of genes in the MAC under different environmental stressors, including nutrient scarcity, extreme temperature, salinity and the presence of ammonia, we identified gene clusters that respond to these external physical or chemical stimulations, and (e) we observed a dramatic increase in HSP70 gene transcription under salinity and chemical stresses but surprisingly, not under temperature changes; we link this temperature-resistance to the evolved loss of temperature stress-sensitive elements in regulatory regions. Together with the genome resources generated in this study, which are available online at Euplotes vannus Genome Database (http://evan.ciliate.org), these data provide molecular evidence for understanding the unique biology of highly adaptable microorganisms
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