Twisting the stacking of layered materials leads to rich new physics. A three-dimensional topological insulator film hosts two-dimensional gapless Dirac electrons on top and bottom surfaces, which, when the film is be...Twisting the stacking of layered materials leads to rich new physics. A three-dimensional topological insulator film hosts two-dimensional gapless Dirac electrons on top and bottom surfaces, which, when the film is below some critical thickness, will hybridize and open a gap in the surface state structure. The hybridization gap can be tuned by various parameters such as film thickness and inversion symmetry, according to the literature. The three-dimensional strong topological insulator Bi(Sb)Se(Te) family has layered structures composed of quintuple layers(QLs) stacked together by van der Waals interaction. Here we successfully grow twistedly stacked Sb_2Te_3 QLs and investigate the effect of twist angels on the hybridization gaps below the thickness limit. It is found that the hybridization gap can be tuned for films of three QLs, which may lead to quantum spin Hall states.Signatures of gap-closing are found in 3-QL films. The successful in situ application of this approach opens a new route to search for exotic physics in topological insulators.展开更多
With high-resolution data of the Magnetospheric Multiscale(MMS) mission, we observe a magnetic flux rope(MFR) in the Earth's magnetosheath. This MFR, showing a clear bipolar variation of the magnetic field in the ...With high-resolution data of the Magnetospheric Multiscale(MMS) mission, we observe a magnetic flux rope(MFR) in the Earth's magnetosheath. This MFR, showing a clear bipolar variation of the magnetic field in the normal component to local current sheet, contains a strong core field. We use the FOTE method to reconstruct the topology of this MFR and find it is consistent with previous expectation. For the first time, the spiral field and core field of the MFR are both revealed from the FOTE method. Comparing topologies reconstructed at different times, we suggest that the axis of the MFR rotates about 88° at different spatial location. Shape and size of the normal projection to axis vary with the spatial location as well. Inside the MFR, a significant increase of plasma density from 40 to 80 cm^(-3), a sharp decrease of ion temperature from 200 to 50 eV, an enhancement of cold ions and a series of filamentary currents are found.展开更多
The linear genome of eukaryotes is partitioned into diverse chromatin states and packaged into a threedimensional(3D)structure,which has functional implications in DNA replication,DNA repair,and transcriptional regula...The linear genome of eukaryotes is partitioned into diverse chromatin states and packaged into a threedimensional(3D)structure,which has functional implications in DNA replication,DNA repair,and transcriptional regulation.Over the past decades,research on plant functional genomics and epigenomics has made great progress,with thousands of genes cloned and molecular mechanisms of diverse biological processes elucidated.Recently,3D genome research has gradually attracted great attention of many plant researchers.Herein,we briefly review the progress in genomic and epigenomic research in plants,with a focus on Arabidopsis and rice,and summarize the currently used technologies and advances in plant 3D genome organization studies.We also discuss the relationships between onedimensional linear genome sequences,epigenomic states,and the 3D chromatin architecture.This review provides basis for future research on plant 3D genomics.展开更多
基金Supported by the National Natural Science Foundation of China (Grant Nos.61804056 and 92065102)。
文摘Twisting the stacking of layered materials leads to rich new physics. A three-dimensional topological insulator film hosts two-dimensional gapless Dirac electrons on top and bottom surfaces, which, when the film is below some critical thickness, will hybridize and open a gap in the surface state structure. The hybridization gap can be tuned by various parameters such as film thickness and inversion symmetry, according to the literature. The three-dimensional strong topological insulator Bi(Sb)Se(Te) family has layered structures composed of quintuple layers(QLs) stacked together by van der Waals interaction. Here we successfully grow twistedly stacked Sb_2Te_3 QLs and investigate the effect of twist angels on the hybridization gaps below the thickness limit. It is found that the hybridization gap can be tuned for films of three QLs, which may lead to quantum spin Hall states.Signatures of gap-closing are found in 3-QL films. The successful in situ application of this approach opens a new route to search for exotic physics in topological insulators.
基金supported by the National Natural Science Foundation of China(Grant Nos.41574153,41431071,and 41404133)
文摘With high-resolution data of the Magnetospheric Multiscale(MMS) mission, we observe a magnetic flux rope(MFR) in the Earth's magnetosheath. This MFR, showing a clear bipolar variation of the magnetic field in the normal component to local current sheet, contains a strong core field. We use the FOTE method to reconstruct the topology of this MFR and find it is consistent with previous expectation. For the first time, the spiral field and core field of the MFR are both revealed from the FOTE method. Comparing topologies reconstructed at different times, we suggest that the axis of the MFR rotates about 88° at different spatial location. Shape and size of the normal projection to axis vary with the spatial location as well. Inside the MFR, a significant increase of plasma density from 40 to 80 cm^(-3), a sharp decrease of ion temperature from 200 to 50 eV, an enhancement of cold ions and a series of filamentary currents are found.
基金supported by the National Natural Science Foundation of China(31771422)the National Key Research and Development Program of China(2016YFD0100904)the open funds of the National Key Laboratory of Crop Genetic Improvement(ZK201906)
文摘The linear genome of eukaryotes is partitioned into diverse chromatin states and packaged into a threedimensional(3D)structure,which has functional implications in DNA replication,DNA repair,and transcriptional regulation.Over the past decades,research on plant functional genomics and epigenomics has made great progress,with thousands of genes cloned and molecular mechanisms of diverse biological processes elucidated.Recently,3D genome research has gradually attracted great attention of many plant researchers.Herein,we briefly review the progress in genomic and epigenomic research in plants,with a focus on Arabidopsis and rice,and summarize the currently used technologies and advances in plant 3D genome organization studies.We also discuss the relationships between onedimensional linear genome sequences,epigenomic states,and the 3D chromatin architecture.This review provides basis for future research on plant 3D genomics.
