Tuning the Chern number in quantum anomalous Hall insulators.

A quantum anomalous Hall (QAH) state is a two-dimensional topological insulating state that has a quantized Hall resistance of h/(Ce2) and vanishing longitudinal resistance under zero magnetic field (where h is the Planck constant, e is the elementary charge, and the Chern number C is an integer)1,2. The QAH effect has been realized in magnetic topological insulators3-9 and magic-angle twisted bilayer graphene10,11. However, the QAH effect at zero magnetic field has so far been realized only for C = 1. Here we realize a well quantized QAH effect with tunable Chern number (up to C = 5) in multilayer structures consisting of alternating magnetic and undoped topological insulator layers, fabricated using molecular beam epitaxy. The Chern number of these QAH insulators is determined by the number of undoped topological insulator layers in the multilayer structure. Moreover, we demonstrate that the Chern number of a given multilayer structure can be tuned by varying either the magnetic doping concentration in the magnetic topological insulator layers or the thickness of the interior magnetic topological insulator layer. We develop a theoretical model to explain our experimental observations and establish phase diagrams for QAH insulators with high, tunable Chern number. The realization of such insulators facilitates the application of dissipationless chiral edge currents in energy-efficient electronic devices, and opens up opportunities for developing multi-channel quantum computing and higher-capacity chiral circuit interconnects.

Electrical switching of the edge current chirality in quantum anomalous Hall insulators.

A quantum anomalous Hall (QAH) insulator is a topological phase in which the interior is insulating but electrical current flows along the edges of the sample in either a clockwise or counterclockwise direction, as dictated by the spontaneous magnetization orientation. Such a chiral edge current eliminates any backscattering, giving rise to quantized Hall resistance and zero longitudinal resistance. Here we fabricate mesoscopic QAH sandwich Hall bar devices and succeed in switching the edge current chirality through thermally assisted spin-orbit torque (SOT). The well-quantized QAH states before and after SOT switching with opposite edge current chiralities are demonstrated through four- and three-terminal measurements. We show that the SOT responsible for magnetization switching can be generated by both surface and bulk carriers. Our results further our understanding of the interplay between magnetism and topological states and usher in an easy and instantaneous method to manipulate the QAH state.

Engineering Plateau Phase Transition in Quantum Anomalous Hall Multilayers.

The plateau phase transition in quantum anomalous Hall (QAH) insulators corresponds to a quantum state wherein a single magnetic domain gives way to multiple domains and then reconverges back to a single magnetic domain. The layer structure of the sample provides an external knob for adjusting the Chern number C of the QAH insulators. Here, we employ molecular beam epitaxy to grow magnetic topological insulator multilayers and realize the magnetic field-driven plateau phase transition between two QAH states with odd Chern number change ΔC. We find that critical exponents extracted for the plateau phase transitions with ΔC = 1 and ΔC = 3 in QAH insulators are nearly identical. We construct a four-layer Chalker-Coddington network model to understand the consistent critical exponents for the plateau phase transitions with ΔC = 1 and ΔC = 3. This work will motivate further investigations into the critical behaviors of plateau phase transitions with different ΔC in QAH insulators.

Coexistence of Superconductivity and Antiferromagnetism in Topological Magnet MnBi2Te4 Films.

The interface of two materials can harbor unexpected emergent phenomena. One example is interface-induced superconductivity. In this work, we employ molecular beam epitaxy to grow a series of heterostructures formed by stacking together two nonsuperconducting antiferromagnetic materials, an intrinsic antiferromagnetic topological insulator MnBi2Te4 and an antiferromagnetic iron chalcogenide FeTe. Our electrical transport measurements reveal interface-induced superconductivity in these heterostructures. By performing scanning tunneling microscopy and spectroscopy measurements, we observe a proximity-induced superconducting gap on the top surface of the MnBi2Te4 layer, confirming the coexistence of superconductivity and antiferromagnetism in the MnBi2Te4 layer. Our findings will advance the fundamental inquiries into the topological superconducting phase in hybrid devices and provide a promising platform for the exploration of chiral Majorana physics in MnBi2Te4-based heterostructures.

Micropterus salmoides rhabdovirus enters cells via clathrin-mediated endocytosis pathway in a pH-, dynamin-, microtubule-, rab5-, and rab7-dependent manner.

IMPORTANCE: Although Micropterus salmoides rhabdovirus (MSRV) causes serious fish epidemics worldwide, the detailed mechanism of MSRV entry into host cells remains unknown. Here, we comprehensively investigated the mechanism of MSRV entry into epithelioma papulosum cyprinid (EPC) cells. This study demonstrated that MSRV enters EPC cells via a low pH, dynamin-dependent, microtubule-dependent, and clathrin-mediated endocytosis. Subsequently, MSRV transports from early endosomes to late endosomes and further into lysosomes in a microtubule-dependent manner. The characterization of MSRV entry will further advance the understanding of rhabdovirus cellular entry pathways and provide novel targets for antiviral drug against MSRV infection.

Proximity-induced superconductivity in epitaxial topological insulator/graphene/gallium heterostructures.

The introduction of superconductivity to the Dirac surface states of a topological insulator leads to a topological superconductor, which may support topological quantum computing through Majorana zero modes1,2. The development of a scalable material platform is key to the realization of topological quantum computing3,4. Here we report on the growth and properties of high-quality (Bi,Sb)2Te3/graphene/gallium heterostructures. Our synthetic approach enables atomically sharp layers at both hetero-interfaces, which in turn promotes proximity-induced superconductivity that originates in the gallium film. A lithography-free, van der Waals tunnel junction is developed to perform transport tunnelling spectroscopy. We find a robust, proximity-induced superconducting gap formed in the Dirac surface states in 5-10 quintuple-layer (Bi,Sb)2Te3/graphene/gallium heterostructures. The presence of a single Abrikosov vortex, where the Majorana zero modes are expected to reside, manifests in discrete conductance changes. The present material platform opens up opportunities for understanding and harnessing the application potential of topological superconductivity.

Electrically Controlled Anomalous Hall Effect and Orbital Magnetization in Topological Magnet MnBi_{2}Te_{4}.

We propose an intrinsic mechanism to understand the even-odd effect, namely, opposite signs of anomalous Hall resistance and different shapes of hysteresis loops for even and odd septuple layers (SLs), of MBE-grown MnBi_{2}Te_{4} thin films with electron doping. The nonzero hysteresis loops in the anomalous Hall effect and magnetic circular dichroism for even-SLs MnBi_{2}Te_{4} films originate from two different antiferromagnetic (AFM) configurations with different zeroth Landau level energies of surface states. The complex form of the anomalous Hall hysteresis loop can be understood from two magnetic transitions, a transition between two AFM states followed by a second transition to the ferromagnetic state. Our model also clarifies the relationship and distinction between axion parameter and magnetoelectric coefficient, and shows an even-odd oscillation behavior of magnetoelectric coefficients in MnBi_{2}Te_{4} films.

Silkworm pupae protein co-degradation by magnetic nanoparticles immobilized proteinase K and Mucor circinelloides aspartic protease for further utilization of sericulture by-products.

Silkworm pupae, by-product of sericulture industry, is massively discarded. The degradation rate of silkworm pupae protein is critical to further employment, which reduces the impact of waste on the environment. Herein, magnetic Janus mesoporous silica nanoparticles immobilized proteinase K mutant T206M and Mucor circinelloides aspartic protease were employed in the co-degradation. The thermostability of T206M improved by enhancing structural rigidity (t1/2 by 30 min and T50 by 5 °C), prompting the degradation efficiency. At 65 °C and pH 7, degradation rate reached the highest of 61.7%, which improved by 26% compared with single free protease degradation. Besides, the immobilized protease is easy to separate and reuse, which maintains 50% activity after 10 recycles. Therefore, immobilized protease co-degradation was first applied to the development and utilization of silkworm pupae resulting in the release of promising antioxidant properties and reduces the environmental impact by utilizing a natural and renewable resource.

Evolution of Dopant-Concentration-Induced Magnetic Exchange Interaction in Topological Insulator Thin Films.

To date, the quantum anomalous Hall effect has been realized in chromium (Cr)- and/or vanadium(V)-doped topological insulator (Bi,Sb)2Te3 thin films. In this work, we use molecular beam epitaxy to synthesize both V- and Cr-doped Bi2Te3 thin films with controlled dopant concentration. By performing magneto-transport measurements, we find that both systems show an unusual yet similar ferromagnetic response with respect to magnetic dopant concentration; specifically the Curie temperature does not increase monotonically but shows a local maximum at a critical dopant concentration. We attribute this unusual ferromagnetic response observed in Cr/V-doped Bi2Te3 thin films to the dopant-concentration-induced magnetic exchange interaction, which displays evolution from van Vleck-type ferromagnetism in a nontrivial magnetic topological insulator to Ruderman-Kittel-Kasuya-Yosida (RKKY)-type ferromagnetism in a trivial diluted magnetic semiconductor. Our work provides insights into the ferromagnetic properties of magnetically doped topological insulator thin films and facilitates the pursuit of high-temperature quantum anomalous Hall effect.

Environmental Doping-Induced Degradation of the Quantum Anomalous Hall Insulators.

The quantum anomalous Hall (QAH) insulator carries dissipation-free chiral edge current and thus provides a unique opportunity to develop energy-efficient transformative information technology. Despite promising advances, the QAH insulator has thus far eluded any practical applications. In addition to its low working temperature, the QAH state in magnetically doped topological insulators usually deteriorates with time in ambient conditions. In this work, we store three QAH devices with similar initial properties in different environments. The QAH device without a protection layer in air shows clear degradation and becomes hole-doped. The QAH device kept in an argon glovebox without a protection layer shows no measurable degradation after 560 h, and the device protected by a 3 nm AlOx protection layer in air shows minimal degradation with stable QAH properties. Our work shows a route to preserve the dissipation-free chiral edge state in QAH devices for potential applications in quantum information technology.

Crossover from Ising- to Rashba-type superconductivity in epitaxial Bi2Se3/monolayer NbSe2 heterostructures.

A topological insulator (TI) interfaced with an s-wave superconductor has been predicted to host topological superconductivity. Although the growth of epitaxial TI films on s-wave superconductors has been achieved by molecular-beam epitaxy, it remains an outstanding challenge for synthesizing atomically thin TI/superconductor heterostructures, which are critical for engineering the topological superconducting phase. Here we used molecular-beam epitaxy to grow Bi2Se3 films with a controlled thickness on monolayer NbSe2 and performed in situ angle-resolved photoemission spectroscopy and ex situ magnetotransport measurements on these heterostructures. We found that the emergence of Rashba-type bulk quantum-well bands and spin-non-degenerate surface states coincides with a marked suppression of the in-plane upper critical magnetic field of the superconductivity in Bi2Se3/monolayer NbSe2 heterostructures. This is a signature of a crossover from Ising- to Rashba-type superconducting pairings, induced by altering the Bi2Se3 film thickness. Our work opens a route for exploring a robust topological superconducting phase in TI/Ising superconductor heterostructures.

Confinement-Induced Chiral Edge Channel Interaction in Quantum Anomalous Hall Insulators.

In quantum anomalous Hall (QAH) insulators, the interior is insulating but electrons can travel with zero resistance along one-dimensional (1D) conducting paths known as chiral edge channels (CECs). These CECs have been predicted to be confined to the 1D edges and exponentially decay in the two-dimensional (2D) bulk. In this Letter, we present the results of a systematic study of QAH devices fashioned in a Hall bar geometry of different widths under gate voltages. At the charge neutral point, the QAH effect persists in a Hall bar device with a width of only ∼72 nm, implying the intrinsic decaying length of CECs is less than ∼36 nm. In the electron-doped regime, we find that the Hall resistance deviates quickly from the quantized value when the sample width is less than 1 µm. Our theoretical calculations suggest that the wave function of CEC first decays exponentially and then shows a long tail due to disorder-induced bulk states. Therefore, the deviation from the quantized Hall resistance in narrow QAH samples originates from the interaction between two opposite CECs mediated by disorder-induced bulk states in QAH insulators, consistent with our experimental observations.

Fluoroscopically guided repositioning of peripherally inserted central catheter in patients failing ultrasound-guided-only placement: a retrospective five-year study.

BACKGROUND: Ultrasound (US)-guided-only insertion at the bedside is safe and improves the success rates of peripherally inserted central catheter (PICC). However, PICC insertion procedures remain challenging for special cases. PURPOSE: To show that fluoroscopically guided tip repositioning, for failed US-guided PICC placement, safely led to satisfactory positioning in difficult cases and, importantly, improved success rates of PICC placements. MATERIAL AND METHODS: A retrospective study of 1560 patients who underwent US-guided PICC placement were performed. Patients who failed US-guided PICC placement were transferred to the interventional radiology department for fluoroscopically guided tip repositioning. Baseline characteristics as well as insertion-related factors were collected. All data were analyzed using SPSS software. RESULTS: In total, 37 (2.4%) patients who failed US-guided PICC placement accepted fluoroscopically guided adjustment or re-insertion. Of these 37 patients, 32 were enrolled. We observed no significant differences between right and left arm PICC access (P > 0.05), even though a higher percentage of PICCs were inserted into left arms (56.3%). The basilic vein (65.6%) was the most common insertion site. Only four patients experienced slight angiospasm (3.1%) and venous thrombosis (9.4%). US-guided PICC insertion failures were primarily due to line tip malposition (84.4%). All patients successfully underwent fluoroscopically guided tip repositioning, which resulted in optimal catheter tip positioning. PICC lines were adjusted in most patients (n=28, 87.5%). CONCLUSION: Malposition was the primary issue causing US-guided PICC insertion failure. Fluoroscopically guided tip repositioning safely and efficaciously led to satisfactory positioning in difficult cases; thus, we recommend this method for patients failing US-guided PICC placement.

[Microbial transformation of artemisinin and its derivatives].

Microbial transformation is an efficient enzymatic approach for the structural modification of exogenous compounds to obtain derivatives. Compared with traditional chemical synthesis, the microbial transformation has in fact the undoubtable advantages of strong region-and stereo-selectivity, and a low environmental and economic impact on the production process, which can achieve the reactions challenging to chemical synthesis. Because microbes are equipped with a broad-spectrum of enzymes and therefore can metabolize various substrates, they are not only a significant route for obtaining novel active derivatives, but also an effective tool for mimicking mammal metabolism in vitro. Artemisinin, a sesquiterpene with a peroxy-bridged structure serving as the main active functional group, is a famous antimalarial agent discovered from Artemisia annua L. Some sesquiterpenoids, such as dihydroartemisinin, artemether, and arteether, have been developed on the basis of artemisinin, which have been successfully marketed and become the first-line antimalarial drugs recommended by WHO. As revealed by pharmacological studies, artemisinin and its derivatives have exhibited extensive biological activities, including antimalarial, antitumor, antiviral, anti-inflammatory, and immunomodulatory. As an efficient approach for structural modification, microbial transformation of artemisinin and its derivatives is an increasingly popular strategy that attracts considerable attention recently, and numerous novel derivatives have been discovered. Herein, this paper reviewed the microbial transformation of artemisinin and its artemisinin, including microbial strains, culture conditions, product isolation and yield, and biological activities, and summarized the advances in microbial transformation in obtaining active derivatives of artemisinin and the simulation of in vivo metabolism of drugs.

Zero Magnetic Field Plateau Phase Transition in Higher Chern Number Quantum Anomalous Hall Insulators.

The plateau-to-plateau transition in quantum Hall effect under high magnetic fields is a celebrated quantum phase transition between two topological states. It can be achieved by either sweeping the magnetic field or tuning the carrier density. The recent realization of the quantum anomalous Hall (QAH) insulators with tunable Chern numbers introduces the channel degree of freedom to the dissipation-free chiral edge transport and makes the study of the quantum phase transition between two topological states under zero magnetic field possible. Here, we synthesized the magnetic topological insulator (TI)/TI pentalayer heterostructures with different Cr doping concentrations in the middle magnetic TI layers using molecular beam epitaxy. By performing transport measurements, we found a potential plateau phase transition between C=1 and C=2 QAH states under zero magnetic field. In tuning the transition, the Hall resistance monotonically decreases from h/e^{2} to h/2e^{2}, concurrently, the longitudinal resistance exhibits a maximum at the critical point. Our results show that the ratio between the Hall resistance and the longitudinal resistance is greater than 1 at the critical point, which indicates that the original chiral edge channel from the C=1 QAH state coexists with the dissipative bulk conduction channels. Subsequently, these bulk conduction channels appear to self-organize and form the second chiral edge channel in completing the plateau phase transition. Our study will motivate further investigations of this novel Chern number change-induced quantum phase transition and advance the development of the QAH chiral edge current-based electronic and spintronic devices.

Chiral-Bubble-Induced Topological Hall Effect in Ferromagnetic Topological Insulator Heterostructures.

We report compelling evidence of an emergent topological Hall effect (THE) from chiral bubbles in a two-dimensional uniaxial ferromagnet, V-doped Sb2Te3 heterostructure. The sign of THE signal is determined by the net curvature of domain walls in different domain configurations, and the strength of THE signal is correlated with the density of nucleation or pinned bubble domains. The experimental results are in good agreement with the integrated linear transport and Monte Carlo simulations, corroborating the emergent gauge field at chiral magnetic bubbles. Our findings not only reveal a general mechanism of THE in two-dimensional ferromagnets but also pave the way for the creation and manipulation of topological spin textures for spintronic applications.

Even-Odd Layer-Dependent Anomalous Hall Effect in Topological Magnet MnBi2Te4 Thin Films.

Recently, MnBi2Te4 has been demonstrated to be an intrinsic magnetic topological insulator and the quantum anomalous Hall (QAH) effect was observed in exfoliated MnBi2Te4 flakes. Here, we used molecular beam epitaxy (MBE) to grow MnBi2Te4 films with thickness down to 1 septuple layer (SL) and performed thickness-dependent transport measurements. We observed a nonsquare hysteresis loop in the antiferromagnetic state for films with thickness greater than 2 SL. The hysteresis loop can be separated into two AH components. We demonstrated that one AH component with the larger coercive field is from the dominant MnBi2Te4 phase, whereas the other AH component with the smaller coercive field is from the minor Mn-doped Bi2Te3 phase. The extracted AH component of the MnBi2Te4 phase shows a clear even-odd layer-dependent behavior. Our studies reveal insights on how to optimize the MBE growth conditions to improve the quality of MnBi2Te4 films.

P300 Participates in Ionizing Radiation-Mediated Activation of Cathepsin L by Mutant p53.

Our previous studies have shown that cathepsin L (CTSL) is involved in the ability of tumors to resist ionizing radiation (IR), but the specific mechanisms responsible for this remain unknown. We report here that mutant p53 (mut-p53) is involved in IR-induced transcription of CTSL. We found that irradiation caused activation of CTSL in mut-p53 cell lines, whereas there was almost no activation in p53 wild-type cell lines. Additionally, luciferase reporter gene assay results demonstrated that IR induced the p53 binding region on the CTSL promoter. We further demonstrated that the expression of p300 and early growth response factor-1 (Egr-1) was upregulated in mut-p53 cell lines after IR treatment. Accordingly, the expression of Ac-H3, Ac-H4, AcH3K9 was upregulated after IR treatment in mut-p53 cell lines, whereas histone deacetylase (HDAC) 4 and HDAC6 were reciprocally decreased. Moreover, knockdown of either Egr-1 or p300 abolished the binding of mut-p53 to the promoter of CTSL. Chromatin immunoprecipitation assay results showed that the IR-activated transcription of CTSL was dependent on p300. To further delineate the clinical relevance of interactions between Egr-1/p300, mut-p53, and CTSL, we accessed primary tumor samples to evaluate the relationships between mut-p53, CTSL, and Egr-1/p300 ex vivo. The results support the notion that mut-p53 is correlated with CTSL transcription involving the Egr-1/p300 pathway. Taken together, the results of our study revealed that p300 is an important target in the process of IR-induced transcription of CTSL, which confirms that CTSL participates in mut-p53 gain-of-function. SIGNIFICANCE STATEMENT: Transcriptional activation of cathepsin L by ionizing radiation required the involvement of mutated p53 and Egr-1/p300. Interference with Egr-1 or p300 could inhibit the expression of cathepsin L induced by ionizing radiation. The transcriptional activation of cathepsin L by p300 may be mediated by p53 binding sites on the cathepsin L promoter.

Concurrence of quantum anomalous Hall and topological Hall effects in magnetic topological insulator sandwich heterostructures.

The quantum anomalous Hall (QAH) effect is a consequence of non-zero Berry curvature in momentum space. The QAH insulator harbours dissipation-free chiral edge states in the absence of an external magnetic field. However, the topological Hall (TH) effect, a hallmark of chiral spin textures, is a consequence of real-space Berry curvature. Here, by inserting a topological insulator (TI) layer between two magnetic TI layers, we realized the concurrence of the TH effect and the QAH effect through electric-field gating. The TH effect is probed by bulk carriers, whereas the QAH effect is characterized by chiral edge states. The appearance of the TH effect in the QAH insulating regime is a consequence of chiral magnetic domain walls that result from the gate-induced Dzyaloshinskii-Moriya interaction and occurs during the magnetization reversal process in the magnetic TI sandwich samples. The coexistence of chiral edge states and chiral spin textures provides a platform for proof-of-concept dissipationless spin-textured spintronic applications.

[A novel flavanone from Thymus przewalskii].

This study was to investigate the chemical constituents from the aerial parts of Thymus przewalskii. The chemical consti-tuents were separated and purified by column chromatography on silica gel, ODS, Sephadex LH-20 and semi-prepared HPLC, and their structures were determined by physicochemical properties and spectroscopic data. Four flavanones were isolated from the ethanol extract of the aerial parts of T. przewalskii, and identified as(2S)-5,6-dihydroxy-7,8,4'-trimethoxyflavanone(1), 5,4'-dihydroxy-6,7-dimethoxyflavanone(2),(2S)-5,4'-dihydroxy-7,8-dimethoxyflavanone(3), sakuranetin(4), respectively. Compound 1 was a new compound and its configuration was determined by CD spectrum, compound 3 was natural product which was isolated for the first time and their configurations were determined by CD spectra. Compound 2 was isolated from the genus Thymus for the first time and compound 4 was isolated from T. przewalskii for the first time. Furthermore, cytotoxicity test was assayed for the four flavanones. They exhibited weak cytotoxicity against human lung cancer cells(A549), with the IC_(50) from 74.5 to 135.6 µmol·L~(-1).