Nonlinear Hall Effects in Strained Twisted Bilayer WSe2_2

Recently, it has been pointed out that the twisting of bilayer WSe$_2$ would generate topologically non-trivial flat bands near the Fermi energy. In this work, we show that twisted bilayer WSe$_2$ (tWSe$_2$) with uniaxial strain exhibits a large nonlinear Hall (NLH) response due to the non-trivial Berry curvatures of the flat bands. Moreover, the NLH effect is greatly enhanced near the topological phase transition point which can be tuned by a vertical displacement field. Importantly, the nonlinear Hall signal changes sign across the topological phase transition point and provides a way to identify the topological phase transition and probe the topological properties of the flat bands. The strong enhancement and high tunability of the NLH effect near the topological phase transition point renders tWSe$_2$ and related moire materials new platforms for rectification and second harmonic generations.Comment: 5 pages, 3 figures. Comments are welcom

Berry curvature, spin Hall effect and nonlinear optical response in moir\'e transition metal dichalcogenide heterobilayers

Recently, the topological flat bands and spin Hall effect have been experimentally observed in the AB-stacked MoTe$_2$/WSe$_2$ heterostructures. In this work, we systematically study the Berry curvature effects in moir\'{e} transition metal dichalcogenide (TMD) heterobilayers. We point out that the moir\'{e} potential of the remote conduction bands would induce a sizable periodic pseudo-magnetic field (PMF) on the valence band. This periodic PMF creates net Berry curvature flux in each valley of the moir\'{e} Brillouin zone. The combination of the effect of the Berry curvature and the spin-valley locking can induce the spin Hall effect being observed in the experiment. Interestingly, the valley-contrasting Berry curvature distribution generated by the PMF can be probed through shift currents, which are DC currents induced by linearly polarized lights through nonlinear responses. Our work shed lights on the novel quantum phenomena induced by Berry curvatures in moir\'e TMD heterobilayers.Comment: 10 pages, 7 figure

Dendrimer conjugates for light-activated delivery of antisense oligonucleotides

PAMAM dendrimer conjugates are used to co-deliver oligonucleotides and photosensitizers to cancer cells. After photo-irradiation, substantial reporter eGFP expression is produced by functional delivery of a model oligonucleotide

Crossover of h/eh/e and h/2eh/2e oscillations in chiral edge-channel Josephson junctions

Recently, several experiments reported that the magnetic field interference pattern of the quantum hall edge states mediated Josephson junctions can exhibit Fraunhofer oscillations with a periodicity of either $h/e$ or $h/2e$. However, a unified understanding of such a phenomenon is still absent. In this work, we show that the competition between local Andreev reflections and crossed Andreev reflections results in the crossover between $h/e$ and $h/2e$ quantum oscillations in chiral edge-channel Josephson junctions. Our theory explains why recent experiments observed either $h/e$ or $h/2e$ oscillations in different samples. Furthermore, we predict a thermal-driven $h/e$ to $h/2e$ Fraunhofer oscillations crossover.Comment: 6 pages, 4 figures, plus Supplementary Materia

Improving mobility of silicon metal-oxide-semiconductor devices for quantum dots by high vacuum activation annealing

To improve mobility of fabricated silicon metal-oxide-semiconductor (MOS) quantum devices, forming gas annealing is a common method used to mitigate the effects of disorder at the Si/SiO2 interface. However, the importance of activation annealing is usually ignored. Here, we show that a high vacuum environment for implantation activation is beneficial for improving mobility compared to nitrogen atmosphere. Low-temperature transport measurements of Hall bars show that peak mobility can be improved by a factor of two, reaching 1.5 m^2/(Vs) using high vacuum annealing during implantation activation. Moreover, the charge stability diagram of a single quantum dot is mapped, with no visible disturbance caused by disorder, suggesting possibility of fabricating high-quality quantum dots on commercial wafers. Our results may provide valuable insights into device optimization in silicon-based quantum computing.Comment: 13 pages, 4 figure

Numerical simulation analysis of four-step variable-diameter pipe by solid-liquid two-phase grinding

In order to investigate the effect of abrasive flow on the polishing effect of variable diameter pipe parts, taking the fourth-order variable-diameter pipe part as the research object, the solid-liquid two-phase abrasive grains are used as the processing method of the fourth-order variable-diameter pipe, the numerical simulation of the machining process of the four-order variable-diameter pipe parts were carried out. Analysis of different inlet speed conditions, the dynamic pressure and the distribution of turbulence intensity of the flow field of the fourth order variable diameter pipe. Through comparative analysis, the effects of the four-stage variable-diameter pipe flow field are studied, which can provide the theoretical basis for the continuous improvement of the abrasive flow precision and ultra precision machining technology, which can improve the efficiency of abrasive flow processing, so that the workpiece fatigue strength is improved, enhance the reliability of the workpiece, extend the service life of the workpiece