Gold-Template-Assisted Mechanical Exfoliation of Large-Area 2D Layers Enables Efficient and Precise Construction of Moiré Superlattices.

Moiré superlattices, consisting of rotationally aligned 2D atomically thin layers, provide a highly novel platform for the study of correlated quantum phenomena. However, reliable and efficient construction of moiré superlattices is challenging because of difficulties to accurately angle-align small exfoliated 2D layers and the need to shun wet-transfer processes. Here, efficient and precise construction of various moiré superlattices is demonstrated by picking up and stacking large-area 2D mono- or few-layer crystals with predetermined crystal axes, made possible by a gold-template-assisted mechanical exfoliation method. The exfoliated 2D layers are semiconductors, superconductors, or magnets and their high quality is confirmed by photoluminescence and Raman spectra and by electrical transport measurements of fabricated field-effect transistors and Hall devices. Twisted homobilayers with angle-twisting accuracy of ≈0.3°, twisted heterobilayers with sub-degree angle-alignment accuracy, and multilayer superlattices are precisely constructed and characterized by their moiré patterns, interlayer excitons, and second harmonic generation. The present study paves the way for exploring emergent phenomena in moiré superlattices.

[Effects of Cytokines on Early Death in Patients with Newly Diagnosed Acute Promyelocytic Leukemia].

OBJECTIVE: To explore the effect of cytokine levels on early death and coagulation function of patients with newly diagnosed acute promyelocytic leukemia (APL). METHODS: Routine examination was performed on 69 newly diagnosed APL patients at admission. Meanwhile, 4 ml fasting venous blood was extracted from the patients. And then the supernatant was taken after centrifugation. The concentrations of cytokines, lactate dehydrogenase (LDH) and ferritin were detected by using the corresponding kits. RESULTS: It was confirmed that cerebral hemorrhage was a major cause of early death in APL patients. Elevated LDH, decreased platelets (PLT) count and prolonged prothrombin time (PT) were high risk factors for early death (P <0.05). The increases of IL-5, IL-6, IL-10, IL-12p70 and IL-17A were closely related to the early death of newly diagnosed APL patients, and the increases of IL-5 and IL-17A also induced coagulation disorder in APL patients by prolonging PT (P <0.05). In newly diagnosed APL patients, ferritin and LDH showed a positive effect on the expression of IL-5, IL-10 and IL-17A, especially ferritin had a highly positive correlation with IL-5 (r =0.867) and IL-17A (r =0.841). Moreover, there was a certain correlation between these five high-risk cytokines, among which IL-5 and IL-17A (r =0.827), IL-6 and IL-10 (r =0.823) were highly positively correlated. CONCLUSION: Elevated cytokine levels in newly diagnosed APL patients increase the risk of early bleeding and death. In addition to the interaction between cytokines themselves, ferritin and LDH positively affect the expression of cytokines, thus affecting the prognosis of APL patients.

Nanoscale Manipulation of Wrinkle-Pinned Vortices in Iron-Based Superconductors.

The controlled manipulation of Abrikosov vortices is essential for both fundamental science and logical applications. However, achieving nanoscale manipulation of vortices while simultaneously measuring the local density of states within them remains challenging. Here, we demonstrate the manipulation of Abrikosov vortices by moving the pinning center, namely one-dimensional wrinkles, on the terminal layers of Fe(Te,Se) and LiFeAs, by utilizing low-temperature scanning tunneling microscopy/spectroscopy (STM/S). The wrinkles trap the Abrikosov vortices induced by the external magnetic field. In some of the wrinkle-pinned vortices, robust zero-bias conductance peaks are observed. We tailor the wrinkle into short pieces and manipulate the wrinkles by using an STM tip. Strikingly, we demonstrate that the pinned vortices move together with these wrinkles even at high magnetic field up to 6 T. Our results provide a universal and effective routine for manipulating wrinkle-pinned vortices and simultaneously measuring the local density of states on the iron-based superconductor surfaces.

Tuning Multiple Landau Quantization in Transition-Metal Dichalcogenide with Strain.

Landau quantization associated with the quantized cyclotron motion of electrons under magnetic field provides the effective way to investigate topologically protected quantum states with entangled degrees of freedom and multiple quantum numbers. Here we report the cascade of Landau quantization in a strained type-II Dirac semimetal NiTe2 with spectroscopic-imaging scanning tunneling microscopy. The uniform-height surfaces exhibit single-sequence Landau levels (LLs) at a magnetic field originating from the quantization of topological surface state (TSS) across the Fermi level. Strikingly, we reveal the multiple sequence of LLs in the strained surface regions where the rotation symmetry is broken. First-principles calculations demonstrate that the multiple LLs attest to the remarkable lifting of the valley degeneracy of TSS by the in-plane uniaxial or shear strains. Our findings pave a pathway to tune multiple degrees of freedom and quantum numbers of TMDs via strain engineering for practical applications such as high-frequency rectifiers, Josephson diode and valleytronics.

Reconstruction of Thiospinel to Active Sites and Spin Channels for Water Oxidation.

Water electrolysis is a promising technique for carbon neutral hydrogen production. A great challenge remains at developing robust and low-cost anode catalysts. Many pre-catalysts are found to undergo surface reconstruction to give high intrinsic activity in the oxygen evolution reaction (OER). The reconstructed oxyhydroxides on the surface are active species and most of them outperform directly synthesized oxyhydroxides. The reason for the high intrinsic activity remains to be explored. Here, a study is reported to showcase the unique reconstruction behaviors of a pre-catalyst, thiospinel CoFe2 S4 , and its reconstruction chemistry for a high OER activity. The reconstruction of CoFe2 S4 gives a mixture with both Fe-S component and active oxyhydroxide (Co(Fe)Ox Hy ) because Co is more inclined to reconstruct as oxyhydroxide, while the Fe is more stable in Fe-S component in a major form of Fe3 S4 . The interface spin channel is demonstrated in the reconstructed CoFe2 S4 , which optimizes the energetics of OER steps on Co(Fe)Ox Hy species and facilitates the spin sensitive electron transfer to reduce the kinetic barrier of O-O coupling. The advantage is also demonstrated in a membrane electrode assembly (MEA) electrolyzer. This work introduces the feasibility of engineering the reconstruction chemistry of the precatalyst for high performance and durable MEA electrolyzers.

Titanium doped kagome superconductor CsV3-xTixSb5 and two distinct phases.

The vanadium-based kagome superconductor CsV3Sb5 has attracted tremendous attention due to its unexcepted anomalous Hall effect (AHE), charge density waves (CDWs), nematicity, and a pseudogap pair density wave (PDW) coexisting with unconventional strong-coupling superconductivity. The origins of CDWs, unconventional superconductivity, and their correlation with different electronic states in this kagome system are of great significance, but so far, are still under debate. Chemical doping in the kagome layer provides one of the most direct ways to reveal the intrinsic physics, but remains unexplored. Here, we report, for the first time, the synthesis of Ti-substituted CsV3Sb5 single crystals and its rich phase diagram mapping the evolution of intertwining electronic states. The Ti atoms directly substitute for V in the kagome layers. CsV3-xTixSb5 shows two distinct superconductivity phases upon substitution. The Ti slightly-substituted phase displays an unconventional V-shaped superconductivity gap, coexisting with weakening CDW, PDW, AHE, and nematicity. The Ti highly-substituted phase has a U-shaped superconductivity gap concomitant with a short-range rotation symmetry breaking CDW, while long-range CDW, twofold symmetry of in-plane resistivity, AHE, and PDW are absent. Furthermore, we also demonstrate the chemical substitution of V atoms with other elements such as Cr and Nb, showing a different modulation on the superconductivity phases and CDWs. These findings open up a way to synthesise a new family of doped CsV3Sb5 materials, and further represent a new platform for tuning the different correlated electronic states and superconducting pairing in kagome superconductors.

Chirality locking charge density waves in a chiral crystal.

In Weyl semimetals, charge density wave (CDW) order can spontaneously break the chiral symmetry, gap out the Weyl nodes, and drive the material into the axion insulating phase. Investigations have however been limited since CDWs are rarely seen in Weyl semimetals. Here, using scanning tunneling microscopy/spectroscopy (STM/S), we report the discovery of a novel unidirectional CDW order on the (001) surface of chiral crystal CoSi - a unique Weyl semimetal with unconventional chiral fermions. The CDW is incommensurate with both lattice momentum and crystalline symmetry directions, and exhibits an intra unit cell π phase shift in the layer stacking direction. The tunneling spectrum shows a particle-hole asymmetric V-shaped energy gap around the Fermi level that modulates spatially with the CDW wave vector. Combined with first-principle calculations, we identify that the CDW is locked to the crystal chirality and is related by a mirror reflection between the two enantiomers of the chiral crystal. Our findings reveal a novel correlated topological quantum state in chiral CoSi crystals and raise the potential for exploring the unprecedented physical behaviors of unconventional chiral fermions.

Observation of an Incommensurate Charge Density Wave in Monolayer TiSe_{2}/CuSe/Cu(111) Heterostructure.

TiSe_{2} is a layered material exhibiting a commensurate (2×2×2) charge density wave (CDW) with a transition temperature of ∼200 K. Recently, incommensurate CDW in bulk TiSe_{2} draws great interest due to its close relationship with the emergence of superconductivity. Here, we report an incommensurate superstructure in monolayer TiSe_{2}/CuSe/Cu(111) heterostructure. Characterizations by low-energy electron diffraction and scanning tunneling microscopy show that the main wave vector of the superstructure is ∼0.41a^{*} or ∼0.59a^{*} (here a^{*} is in-plane reciprocal lattice constant of TiSe_{2}). After ruling out the possibility of moiré superlattices, according to the correlation of the wave vectors of the superstructure and the large indirect band gap below the Fermi level, we propose that the incommensurate superstructure is associated with an incommensurate charge density wave (I-CDW). It is noteworthy that the I-CDW is robust with a transition temperature over 600 K, much higher than that of commensurate CDW in pristine TiSe_{2}. Based on our data and analysis, we present that interface effect may play a key role in the formation of the I-CDW state.

Roton pair density wave in a strong-coupling kagome superconductor.

The transition metal kagome lattice materials host frustrated, correlated and topological quantum states of matter1-9. Recently, a new family of vanadium-based kagome metals, AV3Sb5 (A = K, Rb or Cs), with topological band structures has been discovered10,11. These layered compounds are nonmagnetic and undergo charge density wave transitions before developing superconductivity at low temperatures11-19. Here we report the observation of unconventional superconductivity and a pair density wave (PDW) in CsV3Sb5 using scanning tunnelling microscope/spectroscopy and Josephson scanning tunnelling spectroscopy. We find that CsV3Sb5 exhibits a V-shaped pairing gap Δ ~ 0.5 meV and is a strong-coupling superconductor (2Δ/kBTc ~ 5) that coexists with 4a0 unidirectional and 2a0 × 2a0 charge order. Remarkably, we discover a 3Q PDW accompanied by bidirectional 4a0/3 spatial modulations of the superconducting gap, coherence peak and gap depth in the tunnelling conductance. We term this novel quantum state a roton PDW associated with an underlying vortex-antivortex lattice that can account for the observed conductance modulations. Probing the electronic states in the vortex halo in an applied magnetic field, in strong field that suppresses superconductivity and in zero field above Tc, reveals that the PDW is a primary state responsible for an emergent pseudogap and intertwined electronic order. Our findings show striking analogies and distinctions to the phenomenology of high-Tc cuprate superconductors, and provide groundwork for understanding the microscopic origin of correlated electronic states and superconductivity in vanadium-based kagome metals.

Spin pinning effect to reconstructed oxyhydroxide layer on ferromagnetic oxides for enhanced water oxidation.

Producing hydrogen by water electrolysis suffers from the kinetic barriers in the oxygen evolution reaction (OER) that limits the overall efficiency. With spin-dependent kinetics in OER, to manipulate the spin ordering of ferromagnetic OER catalysts (e.g., by magnetization) can reduce the kinetic barrier. However, most active OER catalysts are not ferromagnetic, which makes the spin manipulation challenging. In this work, we report a strategy with spin pinning effect to make the spins in paramagnetic oxyhydroxides more aligned for higher intrinsic OER activity. The spin pinning effect is established in oxideFM/oxyhydroxide interface which is realized by a controlled surface reconstruction of ferromagnetic oxides. Under spin pinning, simple magnetization further increases the spin alignment and thus the OER activity, which validates the spin effect in rate-limiting OER step. The spin polarization in OER highly relies on oxyl radicals (O∙) created by 1st dehydrogenation to reduce the barrier for subsequent O-O coupling.

Spin-polarized oxygen evolution reaction under magnetic field.

The oxygen evolution reaction (OER) is the bottleneck that limits the energy efficiency of water-splitting. The process involves four electrons' transfer and the generation of triplet state O2 from singlet state species (OH- or H2O). Recently, explicit spin selection was described as a possible way to promote OER in alkaline conditions, but the specific spin-polarized kinetics remains unclear. Here, we report that by using ferromagnetic ordered catalysts as the spin polarizer for spin selection under a constant magnetic field, the OER can be enhanced. However, it does not applicable to non-ferromagnetic catalysts. We found that the spin polarization occurs at the first electron transfer step in OER, where coherent spin exchange happens between the ferromagnetic catalyst and the adsorbed oxygen species with fast kinetics, under the principle of spin angular momentum conservation. In the next three electron transfer steps, as the adsorbed O species adopt fixed spin direction, the OER electrons need to follow the Hund rule and Pauling exclusion principle, thus to carry out spin polarization spontaneously and finally lead to the generation of triplet state O2. Here, we showcase spin-polarized kinetics of oxygen evolution reaction, which gives references in the understanding and design of spin-dependent catalysts.

Observation of magnetic adatom-induced Majorana vortex and its hybridization with field-induced Majorana vortex in an iron-based superconductor.

Braiding Majorana zero modes is essential for fault-tolerant topological quantum computing. Iron-based superconductors with nontrivial band topology have recently emerged as a surprisingly promising platform for creating distinct Majorana zero modes in magnetic vortices in a single material and at relatively high temperatures. The magnetic field-induced Abrikosov vortex lattice makes it difficult to braid a set of Majorana zero modes or to study the coupling of a Majorana doublet due to overlapping wave functions. Here we report the observation of the proposed quantum anomalous vortex with integer quantized vortex core states and the Majorana zero mode induced by magnetic Fe adatoms deposited on the surface. We observe its hybridization with a nearby field-induced Majorana vortex in iron-based superconductor FeTe0.55Se0.45. We also observe vortex-free Yu-Shiba-Rusinov bound states at the Fe adatoms with a weaker coupling to the substrate, and discover a reversible transition between Yu-Shiba-Rusinov states and Majorana zero mode by manipulating the exchange coupling strength. The dual origin of the Majorana zero modes, from magnetic adatoms and external magnetic field, provides a new single-material platform for studying their interactions and braiding in superconductors bearing topological band structures.

One-dimensional weak antilocalization effect in 1T'-MoTe2nanowires grown by chemical vapor deposition.

We present a chemical vapor deposition method for the synthesizing of single-crystal 1T'-MoTe2nanowires and the observation of one-dimensional weak antilocalization effect in 1T'-MoTe2nanowires for the first time. The diameters of the 1T'-MoTe2nanowires can be controlled by changing the flux of H2/Ar carrier gas. Spherical-aberration-corrected transmission electron microscopy, selected area electron diffraction and energy dispersive x-ray spectroscopy (EDS) reveal the 1T' phase and the atomic ratio of Te/Mo closing to 2:1. The resistivity of 1T'-MoTe2nanowires shows metallic behavior and agrees well with the Fermi liquid theory (<20 K). The coherence length extracted from 1D Hikami-Larkin-Nagaoka model with the presence of strong spin-orbit coupling is proportional toT-0.36, indicating a Nyquist electron-electron interaction dephasing mechanism at one dimension. These results provide a feasible way to prepare one-dimensional topological materials and is promising for fundamental study of the transport properties.

Insulating SiO2 under Centimeter-Scale, Single-Crystal Graphene Enables Electronic-Device Fabrication.

Graphene on SiO2 enables fabrication of Si-technology-compatible devices, but a transfer of these devices from other substrates and direct growth have severe limitations due to a relatively small grain size or device-contamination. Here, we show an efficient, transfer-free way to integrate centimeter-scale, single-crystal graphene, of a quality suitable for electronic devices, on an insulating SiO2 film. Starting with single-crystal graphene grown epitaxially on Ru(0001), a SiO2 film is grown under the graphene by stepwise intercalation of silicon and oxygen. Thin (∼1 nm) crystalline or thicker (∼2 nm) amorphous SiO2 has been produced. The insulating nature of the thick amorphous SiO2 is verified by transport measurements. The device-quality of the corresponding graphene was confirmed by the observation of Shubnikov-de Haas oscillations, an integer quantum Hall effect, and a weak antilocalization effect within in situ fabricated Hall bar devices. This work provides a reliable platform for applications of large-scale, high-quality graphene in electronics.

Localized spin-orbit polaron in magnetic Weyl semimetal Co3Sn2S2.

The kagome lattice Co3Sn2S2 exhibits the quintessential topological phenomena of a magnetic Weyl semimetal such as the chiral anomaly and Fermi-arc surface states. Probing its magnetic properties is crucial for understanding this correlated topological state. Here, using spin-polarized scanning tunneling microscopy/spectroscopy (STM/S) and non-contact atomic force microscopy (nc-AFM) combined with first-principle calculations, we report the discovery of localized spin-orbit polarons (SOPs) with three-fold rotation symmetry nucleated around single S-vacancies in Co3Sn2S2. The SOPs carry a magnetic moment and a large diamagnetic orbital magnetization of a possible topological origin associated relating to the diamagnetic circulating current around the S-vacancy. Appreciable magneto-elastic coupling of the SOP is detected by nc-AFM and STM. Our findings suggest that the SOPs can enhance magnetism and more robust time-reversal-symmetry-breaking topological phenomena. Controlled engineering of the SOPs may pave the way toward practical applications in functional quantum devices.

Ferroelectric-Gated InSe Photodetectors with High On/Off Ratios and Photoresponsivity.

Indium selenide (InSe) has a high electron mobility and tunable direct band gap, enabling its potential applications to electronic and optoelectronic devices. Here, we report the fabrication of InSe photodetectors with high on/off ratios and ultrahigh photoresponsivity, using ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer films as the top-gate dielectric. Benefiting from the successful suppression of the dark current down to ∼10-14A in the InSe channel by tuning the three different polarization states in ferroelectric P(VDF-TrFE) and improved interface properties using h-BN as a substrate, the ferroelectric-gated InSe photodetectors show a high on/off ratio of over 108, a high photoresponsivity up to 14 250 AW-1, a high detectivity up to 1.63 × 1013 Jones, and a fast response time of 600 µs even at zero-gate voltage. The present results highlight the role of ferroelectric P(VDF-TrFE) in tuning the carrier transport of InSe and may provide an avenue for the development of InSe-based photodetectors.

Nearly quantized conductance plateau of vortex zero mode in an iron-based superconductor.

Majorana zero modes (MZMs) are spatially localized, zero-energy fractional quasiparticles with non-Abelian braiding statistics that hold promise for topological quantum computing. Owing to the particle-antiparticle equivalence, MZMs exhibit quantized conductance at low temperature. By using variable-tunnel-coupled scanning tunneling spectroscopy, we studied tunneling conductance of vortex bound states on FeTe0.55Se0.45 superconductors. We report observations of conductance plateaus as a function of tunnel coupling for zero-energy vortex bound states with values close to or even reaching the 2e 2/h quantum conductance (where e is the electron charge and h is Planck's constant). By contrast, no plateaus were observed on either finite energy vortex bound states or in the continuum of electronic states outside the superconducting gap. This behavior of the zero-mode conductance supports the existence of MZMs in FeTe0.55Se0.45.

Observation of the Kondo Effect in Multilayer Single-Crystalline VTe2 Nanoplates.

We report the chemical vapor deposition (CVD) growth, characterization, and low-temperature magnetotransport of 1T phase multilayer single-crystalline VTe2 nanoplates. The transport studies reveal that no sign of intrinsic long-range ferromagnetism but localized magnetic moments exist in the individual multilayer metallic VTe2 nanoplates. The localized moments give rise to the Kondo effect, evidenced by logarithmical increment of resistivity with decreasing temperature and negative magnetoresistance (NMR) regardless of the direction of magnetic field at temperatures below the resistivity minimum. The low-temperature resistivity upturn is well described by the Hamann equation, and the NMR at different temperatures, a manifestation of the magnetization of the localized spins, is well fitted to a Brillouin function for S = 1/2. Density functional theory calculations reveal that the localized magnetic moments mainly come from the interstitial vanadium ions in the VTe2 nanoplates. Our results will shed light on the study of magnetic properties, strong correlation, and many-body physics in two-dimensional metallic transition metal dichalcogenides.

Quasi-2D Transport and Weak Antilocalization Effect in Few-layered VSe2.

With strong spin-orbit coupling (SOC), ultrathin two-dimensional (2D) transitional metal chalcogenides (TMDs) are predicted to exhibit weak antilocalization (WAL) effect at low temperatures. The observation of WAL effect in VSe2 is challenging due to the relative weak SOC and three-dimensional (3D) transport nature in thick VSe2. Here, we report on the observation of quasi-2D transport and WAL effect in sublimed-salt-assisted low-temperature chemical vapor deposition (CVD) grown few-layered high-quality VSe2 nanosheets. The WAL magnitudes in magnetoconductance can be perfectly fitted by the 2D Hikami-Larkin-Nagaoka (HLN) equation in the presence of strong SOC, by which the spin-orbit scattering length lSO and phase coherence length lϕ have been extracted. The phase coherence length lϕ shows a power law dependence with temperature, lϕ∼ T-1/2, revealing an electron-electron interaction-dominated dephasing mechanism. Such sublimed-salt-assisted growth of high-quality few-layered VSe2 and the observation of WAL pave the way for future spintronic and valleytronic applications.

Plasmon-induced hot electron transfer in Au-ZnO heterogeneous nanorods for enhanced SERS.

Colloid-synthesized matchstick-shaped Au-ZnO heterogeneous nanorods are found to have the Zn ion terminated plane in the ZnO-Au interface without the formation of Au-O bonds based on the atomic-resolution observation of their interfacial structure and electronic states, which is greatly different from the other reported results. The Au-ZnO heterogeneous nanorods with a good expitaxial interface have shown a stronger surface-enhanced Raman scattering (SERS) signal of the dopamine molecules than Au nanoscale seeds alone, which is attributed to the enhanced charge transfer (CT) effect of ZnO which is greatly improved by the plasmon-induced hot electron from Au nanostructures. The enhanced CT effect has also been proved by a higher photocatalysis efficiency. Furthermore, the plasmon-induced hot electron transfer mechanism in Au-ZnO heterogeneous nanorods has been confirmed by a slow rise time of electrons in the transient absorption measurements. These findings suggest the dependency of the plasmon-induced hot electron transfer mechanism on the different mixing of the metal and semiconductor band levels.