208 research outputs found
Correlated states in twisted double bilayer graphene
Electron-electron interactions play an important role in graphene and related
systems and can induce exotic quantum states, especially in a stacked bilayer
with a small twist angle. For bilayer graphene where the two layers are twisted
by a "magic angle", flat band and strong many-body effects lead to correlated
insulating states and superconductivity. In contrast to monolayer graphene, the
band structure of untwisted bilayer graphene can be further tuned by a
displacement field, providing an extra degree of freedom to control the flat
band that should appear when two bilayers are stacked on top of each other.
Here, we report the discovery and characterization of such displacement-field
tunable electronic phases in twisted double bilayer graphene. We observe
insulating states at a half-filled conduction band in an intermediate range of
displacement fields. Furthermore, the resistance gap in the correlated
insulator increases with respect to the in-plane magnetic fields and we find
that the g factor according to spin Zeeman effect is ~2, indicating spin
polarization at half filling. These results establish the twisted double
bilayer graphene as an easily tunable platform for exploring quantum many-body
states
On-Site Quantification and Infection Risk Assessment of Airborne SARS-CoV-2 Virus Via a Nanoplasmonic Bioaerosol Sensing System in Healthcare Settings
On-site quantification and early-stage infection risk assessment of airborne severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) with high spatiotemporal resolution is a promising approach for mitigating the spread of coronavirus disease 2019 (COVID-19) pandemic and informing life-saving decisions. Here, a condensation (hygroscopic growth)-assisted bioaerosol collection and plasmonic photothermal sensing (CAPS) system for on-site quantitative risk analysis of SARS-CoV-2 virus-laden aerosols is presented. The CAPS system provided rapid thermoplasmonic biosensing results after an aerosol-to-hydrosol sampling process in COVID-19-related environments including a hospital and a nursing home. The detection limit reached 0.25 copies/µL in the complex aerosol background without further purification. More importantly, the CAPS system enabled direct measurement of the SARS-CoV-2 virus exposures with high spatiotemporal resolution. Measurement and feedback of the results to healthcare workers and patients via a QR-code are completed within two hours. Based on a dose-responseµ model, it is used the plasmonic biosensing signal to calculate probabilities of SARS-CoV-2 infection risk and estimate maximum exposure durations to an acceptable risk threshold in different environmental settings
Factors affecting the early establishment of neonatal intestinal flora and its intervention measures
In recent years, it has become evident that early-life intestinal flora plays a pivotal role in determining human health. Consequently, it is imperative to explore the establishment of neonatal intestinal flora and its influencing factors. Early neonatal intestinal flora is influenced by a multitude of factors, including maternal and infant-related factors, as well as external environment. This review summarizes the colonization mechanism of intestinal flora in the early life of newborns and discussed their influence on the establishment of neonatal intestinal flora, taking into account factors such as delivery mode, gestational age and feeding mode. Additionally, this review delves into the natural or artificial reconstruction of intestinal flora colonization defects in infants born via cesarean section and premature infants, with the goal of establishing a theoretical foundation for preventing and treating issues related to neonatal intestinal flora colonization and associated diseases
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The NMDA receptor intracellular C-terminal domains reciprocally interact with allosteric modulators
N-methyl-d-aspartate receptors (NMDARs) have multiple prominent roles in CNS function but their excessive or insufficient activity contributes to neuropathological/psychiatric disorders. Consequently, a variety of positive and negative allosteric modulators (PAMs and NAMs, respectively) have recently been developed. Although these modulators bind to extracellular domains, in the present report we find that the NMDAR's intracellular C-terminal domains (CTDs) significantly influence PAM/NAM activity. GluN2 CTD deletion robustly affected NAM and PAM activity with both enhancing and inhibiting effects that were compound-specific and NMDAR subunit-specific. In three cases, individual PAMs became NAMs at specific GluN2-truncated receptors. In contrast to GluN2, GluN1 CTD removal only reduced PAM activity of UBP684 and CIQ, and did not affect NAM activity. Consistent with these findings, agents altering phosphorylation state or intracellular calcium levels displayed receptor-specific and compound-specific effects on PAM activity. It is possible that the GluN2's M4 domain transmits intracellular modulatory signals from the CTD to the M1/M4 channel gating machinery and that this site is a point of convergence in the direct or indirect actions of several PAMs/NAMs thus rendering them sensitive to CTD status. Thus, allosteric modulators are likely to have a marked and varied sensitivity to post-translational modifications, protein-protein associations, and intracellular ions. The interaction between PAM activity and NMDAR CTDs appears reciprocal. GluN1 CTD-deletion eliminated UBP684, but not pregnenolone sulfate (PS), PAM activity. And, in the absence of agonists, UBP684, but not PS, was able to promote movement of fluorescently-tagged GluN1-CTDs. Thus, it may be possible to pharmacologically target NMDAR metabotropic activity in the absence of channel activation
Layer-by-Layer Epitaxy of Multilayer MoS2 Wafers
Two-dimensional (2D) semiconductor of MoS2 has great potential for advanced
electronics technologies beyond silicon1-9. So far, high-quality monolayer MoS2
wafers10-12 are already available and various demonstrations from individual
transistors to integrated circuits have also been shown13-15. In addition to
the monolayer, multilayers have narrower band gaps but improved carrier
mobilities and current capacities over the monolayer5,16-18. However, achieving
high-quality multilayer MoS2 wafers remains a challenge. Here we report the
growth of high quality multilayer MoS2 4-inch wafers via the layer-by-layer
epitaxy process. The epitaxy leads to well-defined stacking orders between
adjacent epitaxial layers and offers a delicate control of layer numbers up to
6. Systematic evaluations on the atomic structures and electronic properties
were carried out for achieved wafers with different layer numbers. Significant
improvements on device performances were found in thicker-layer field effect
transistors (FETs), as expected. For example, the average field-effect mobility
({\mu}FE) at room temperature (RT) can increase from ~80 cm2V-1s-1 for
monolayer to ~110/145 cm2V-1s-1 for bilayer/trilayer devices. The highest RT
{\mu}FE=234.7 cm2V-1s-1 and a record-high on-current densities of 1.704
mA{\mu}m-1 at Vds=2 V were also achieved in trilayer MoS2 FETs with a high
on/off ratio exceeding 107. Our work hence moves a step closer to practical
applications of 2D MoS2 in electronics.Comment: 13 pages,4 Figure
Room-temperature correlated states in twisted bilayer MoS
Moir\'e superlattices have emerged as an exciting condensed-matter quantum
simulator for exploring the exotic physics of strong electronic correlations.
Notable progress has been witnessed, but such correlated states are achievable
usually at low temperatures. Here, we report the transport evidences of
room-temperature correlated electronic states and layer-hybridized SU(4)
Hubbard model simulator in AB-stacked MoS homo-bilayer moir\'e
superlattices. Correlated insulating states at moir\'e band filling factors v =
1, 2, 3 are unambiguously established in twisted bilayer MoS. Remarkably,
the correlated electronic states can persist up to a record-high critical
temperature of over 285 K. The realization of room-temperature correlated
states in twisted bilayer MoS can be understood as the cooperation effects
of the stacking-specific atomic reconstruction and the resonantly enhanced
interlayer hybridization, which largely amplify the moir\'e superlattice
effects on electronic correlations. Furthermore, extreme large non-linear Hall
responses up to room-temperature are uncovered near correlated insulating
states, demonstrating the quantum geometry of moir\'e flat conduction band.Comment: 13 pages, 3 figure
Current-driven magnetization switching in a van der Waals ferromagnet Fe3GeTe2
The recent discovery of ferromagnetism in two-dimensional (2D) van der Waals
(vdW) materials holds promises for novel spintronic devices with exceptional
performances. However, in order to utilize 2D vdW magnets for building
spintronic nanodevices such as magnetic memories, key challenges remain in
terms of effectively switching the magnetization from one state to the other
electrically. Here, we devise a bilayer structure of Fe3GeTe2/Pt, in which the
magnetization of few-layered Fe3GeTe2 can be effectively switched by the
spin-orbit torques (SOTs) originated from the current flowing in the Pt layer.
The effective magnetic fields corresponding to the SOTs are further
quantitatively characterized using harmonic measurements. Our demonstration of
the SOT-driven magnetization switching in a 2D vdW magnet could pave the way
for implementing low-dimensional materials in the next-generation spintronic
applications
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