157 research outputs found
Anomalous light cones and valley optical selection rules of interlayer excitons in twisted heterobilayers
We show that, because of the inevitable twist and lattice mismatch in
heterobilayers of transition metal dichalcogenides, interlayer excitons have
six-fold degenerate light cones anomalously located at finite velocities on the
parabolic energy dispersion. The photon emissions at each light cone are
elliptically polarized, with major axis locked to the direction of exciton
velocity, and helicity specified by the valley indices of the electron and the
hole. These finite-velocity light cones allow unprecedented possibilities to
optically inject valley polarization and valley current, and the observation of
both direct and inverse valley Hall effects, by exciting interlayer excitons.
Our findings suggest potential excitonic circuits with valley functionalities,
and unique opportunities to study exciton dynamics and condensation phenomena
in semiconducting 2D heterostructures.Comment: Including the Supplemental Material
Spin-valley qubit in nanostructures of monolayer semiconductors: Optical control and hyperfine interaction
We investigate the optical control possibilities of spin-valley qubit carried
by single electrons localized in nanostructures of monolayer TMDs, including
small quantum dots formed by lateral heterojunction and charged impurities. The
quantum controls are discussed when the confinement induces valley
hybridization and when the valley hybridization is absent. We show that the
bulk valley and spin optical selection rules can be inherited in different
forms in the two scenarios, both of which allow the definition of spin-valley
qubit with desired optical controllability. We also investigate nuclear spin
induced decoherence and quantum control of electron-nuclear spin entanglement
via intervalley terms of the hyperfine interaction. Optically controlled
two-qubit operations in a single quantum dot are discussed.Comment: 17pages, 10 figure
Correlation-induced symmetry-broken states in large-angle twisted bilayer graphene on MoS2
Strongly correlated states are commonly emerged in twisted bilayer graphene
(TBG) with magic-angle, where the electron-electron (e-e) interaction U becomes
prominent relative to the small bandwidth W of the nearly flat band. However,
the stringent requirement of this magic angle makes the sample preparation and
the further application facing great challenges. Here, using scanning tunneling
microscopy (STM) and spectroscopy (STS), we demonstrate that the
correlation-induced symmetry-broken states can also be achieved in a 3.45{\deg}
TBG, via engineering this non-magic-angle TBG into regimes of U/W > 1. We
enhance the e-e interaction through controlling the microscopic dielectric
environment by using a MoS2 substrate. Simultaneously, the bandwidth of the
low-energy van Hove singularity (VHS) peak is reduced by enhancing the
interlayer coupling via STM tip modulation. When partially filled, the VHS peak
exhibits a giant splitting into two states flanked the Fermi level and shows a
symmetry-broken LDOS distribution with a stripy charge order, which confirms
the existence of strong correlation effect in our 3.45{\deg} TBG. Our result
paves the way for the study and application of the correlation physics in TBGs
with a wider range of twist angle
In-Plane Anisotropies of Polarized Raman Response and Electrical Conductivity in Layered Tin Selenide
The group IV-VI compound SnSe, with an orthorhombic lattice structure, has
recently attracted particular interest due to its unexpectedly low thermal
conductivity and high power factor, showing great promise for thermoelectric
applications. SnSe displays intriguing anisotropic properties due to the
puckered low-symmetry in-plane lattice structure. Low-dimensional materials
have potential advantages in improving the efficiency of thermoelectric
conversion, due to the increased power factor and decreased thermal
conductivity. A complete study of the optical and electrical anisotropies of
SnSe nanostructures is a necessary prerequisite in taking advantage of the
material properties for high performance devices. Here, we synthesize the
single crystal SnSe nanoplates (NPs) by chemical vapor deposition. The angular
dependence of the polarized Raman spectra of SnSe NPs shows anomalous
anisotropic light-mater interaction. The angle-resolved charge transport of the
SnSe NPs expresses a strong anisotropic conductivity behavior. These studies
elucidate the anisotropic interactions which will be of use for future
ultrathin SnSe in electronic, thermoelectric and optoelectronic devices.Comment: 25 pages, 9 figures, 3 table
Complete chloroplast genome sequences of Dioscorea: Characterization, genomic resources, and phylogenetic analyses
Dioscorea L., the largest genus of the family Dioscoreaceae with over 600 species, is not only an important food but also a medicinal plant. The identification and classification of Dioscorea L. is a rather difficult task. In this study, we sequenced five Dioscorea chloroplast genomes, and analyzed with four other chloroplast genomes of Dioscorea species from GenBank. The Dioscorea chloroplast genomes displayed the typical quadripartite structure of angiosperms, which consisted of a pair of inverted repeats separated by a large single-copy region, and a small single-copy region. The location and distribution of repeat sequences and microsatellites were determined, and the rapidly evolving chloroplast genome regions (trnK-trnQ, trnS-trnG, trnC-petN, trnE-trnT, petG-trnW-trnP, ndhF, trnL-rpl32, and ycf1) were detected. Phylogenetic relationships of Dioscorea inferred from chloroplast genomes obtained high support even in shortest internodes. Thus, chloroplast genome sequences provide potential molecular markers and genomic resources for phylogeny and species identification
Production and decay of the neutral top-pion in high energy colliders
We study the production and decay of the neutral top-pion
predicted by topcolor-assisted technicolor(TC2) theory. Our results show that,
except the dominant decay modes , and , the
can also decay into and modes. It can
be significantly produced at high energy collider(LC) experiments
via the processes and . We further calculate the production cross sections of the
processes and . We find that the signatures of the neutral top-pion
can be detected via these processes.Comment: Latex file, 13 Pages, 6 eps figures. to be published in Phys.Rev.
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