9 research outputs found
Moir\'e excitons: from programmable quantum emitter arrays to spin-orbit coupled artificial lattices
Highly uniform and ordered nanodot arrays are crucial for high performance
quantum optoelectronics including new semiconductor lasers and single photon
emitters, and for synthesizing artificial lattices of interacting
quasiparticles towards quantum information processing and simulation of
many-body physics. Van der Waals heterostructures of 2D semiconductors are
naturally endowed with an ordered nanoscale landscape, i.e. the moir\'e pattern
that laterally modulates electronic and topographic structures. Here we find
these moir\'e effects realize superstructures of nanodot confinements for
long-lived interlayer excitons, which can be either electrically or strain
tuned from perfect arrays of quantum emitters to excitonic superlattices with
giant spin-orbit coupling (SOC). Besides the wide range tuning of emission
wavelength, the electric field can also invert the spin optical selection rule
of the emitter arrays. This unprecedented control arises from the gauge
structure imprinted on exciton wavefunctions by the moir\'e, which underlies
the SOC when hopping couples nanodots into superlattices. We show that the
moir\'e hosts complex-hopping honeycomb superlattices, where exciton bands
feature a Dirac node and two Weyl nodes, connected by spin-momentum locked
topological edge modes.Comment: To appear in Science Advance
Inheritance of the exciton geometric structure from Bloch electrons in two-dimensional layered semiconductors
We theoretically studied the exciton geometric structure in layered
semiconducting transition metal dichalcogenides. Using the well-developed
three-orbital tight-binding models for the electron and hole constituents, an
effective exciton Hamiltonian can be constructed and solved perturbatively. We
show that the electron-hole Coulomb interaction gives rise to a non-trivial
inheritance of the exciton geometric structure from Bloch electrons, which
manifests as a center-of-mass anomalous Hall velocity of the exciton when two
external fields are applied on the electron and hole constituents,
respectively. The form of the center-of-mass anomalous velocity is obtained,
which is found to exhibit a non-trivial dependence on the fields as well as the
exciton wave function
Melting of electronic and excitonic crystals in 2D semiconductor moir\'e patterns: a perspective from the Lindemann criterion
Using the Lindemann criterion, we analyzed the quantum and thermal melting of
electronic and excitonic crystals recently discovered in 2D semiconductor
moir\'e patterns. We show that the finite 2D screening of the atomically thin
material can suppress (enhance) the inter-site Coulomb (dipolar) interaction
strength, thus inhibits (facilitates) the formation of the electronic
(excitonic) crystal. Meanwhile, a strong enough moir\'e confinement is found to
be essential for realizing the crystal phase with a lattice constant near 10 nm
or shorter. From the calculated Lindemann ratio which quantifies the
fluctuation of the site displacement, we estimate that the crystal will melt
into a liquid above a temperature in the order of several tens Kelvin
Heterologous Expression and Enzymatic Properties of Nicotinamide Nucleoside Kinase from Saccharomyces cerevisiae
In this study, the nicotinamide riboside kinase 1 gene (ScNRK1) was cloned from Saccharomyces cerevisiae, and its soluble expression in Escherichia coli was achieved using pET28a plasmid. The enzyme activity in the fermentation broth was 14.75 IU/mL, and the specific activity the purified enzyme was 2 252.59 IU/mg. In addition, the kinetic parameters of ScNRK1 were significantly higher than those of other reported nicotinamide nucleoside kinases, so ScNRK1 could be more advantageous in the enzymatic synthesis of nicotinamide mononucleotide (NMN)
Behavior of solid matters and heavy metals during conductive drying process of sewage sludge
Behavior of solid matters and heavy metals during conductive drying process of sewage sludge was evaluated in a sewage sludge disposal center in Beijing, China. The results showed most of solid matters could be retained in the dried sludge after drying. Just about 3.1% of solid matters were evaporated with steam mainly by the form of volatile fatty acids. Zn was the dominant heavy metal in the sludge, followed by Cu, Cr, Pb, Ni, Hg, and Cd. The heavy metals in the condensate were all below the detection limit except Hg. Hg in the condensate accounted for less than 0.1% of the total Hg. It can be concluded that most of the heavy metals are also retained in the dried sludge during the drying process, but their bioavailability could be changed significantly. The results are useful for sewage sludge utilization and its condensate treatment