Fourfold Symmetric Superconductivity in Spinel Oxide LiTi2O4(001) Thin Films.

The charge frustration with the mixed-valence state inherent to LiTi2O4, which is found to be the only oxide superconductor with spinel structure, is the impetus for paying special attention to unveil the underlying intriguing superconducting properties. Here, we report a pronounced fourfold rotational symmetry of the superconductivity in high-quality single-crystalline LiTi2O4(001) thin films. Both the magnetoresistivity and upper critical field under an applied magnetic field manifest striking fourfold oscillations deep inside the superconducting state, whereas the anisotropy vanishes in the normal state, demonstrating that it is an intrinsic property of the superconducting phase. We attribute this behavior to the unconventional d-wave superconducting Cooper pairs with the irreducible representation of Eg protected by the Oh point group in cubic LiTi2O4. Our findings show the nontrivial character of the pairing interaction in a three-dimensional spinel oxide superconductor.

Breakfast Consumption and Academic Achievement Among Chinese Adolescents: A Moderated Mediation Model.

The studies have shown that a healthy lifestyle has a significant impact on the academic achievement of adolescents. Behavior of breakfast eating is considered a hallmark of dietary patterns and an important component of a healthy lifestyle. The prior study explained that students had a lower level of achievement motivation at school because they were exposed to some militating factors in their families such as absenteeism, ill health, malnutrition, and hunger. This study examined the mediating role of achievement motivation and moderating role of socioeconomic status (SES) in the association between breakfast consumption and academic achievement. This study used a sample of 15-year-old Chinese students who participated in Program for International Student Assessment (PISA) 2015. In terms of gender, female students accounted for 47.2% and male students accounted for 52.8%. The results showed that (1) breakfast consumption had a positive predictive effect on academic achievement; (2) achievement motivation played a partial mediating role in the relationship between breakfast consumption and academic achievement; and (3) the direct and indirect effects were moderated by the SES of students, which meant that the effect of breakfast consumption on achievement motivation can differ depending on the SES of students. Besides, both the effects were stronger for individuals with higher SES. The conclusion of this study has an important theoretical value and reference value to guide the Chinese parents and Chinese adolescents to pay more attention to breakfast consumption and healthy lifestyles.

Coexistence of Topological Edge State and Superconductivity in Bismuth Ultrathin Film.

Ultrathin freestanding bismuth film is theoretically predicted to be one kind of two-dimensional topological insulators. Experimentally, the topological nature of bismuth strongly depends on the situations of the Bi films. Film thickness and interaction with the substrate often change the topological properties of Bi films. Using angle-resolved photoemission spectroscopy, scanning tunneling microscopy or spectroscopy and first-principle calculation, the properties of Bi(111) ultrathin film grown on the NbSe2 superconducting substrate have been studied. We find the band structures of the ultrathin film is quasi-freestanding, and one-dimensional edge state exists on Bi(111) film as thin as three bilayers. Superconductivity is also detected on different layers of the film and the pairing potential exhibits an exponential decay with the layer thicknesses. Thus, the topological edge state can coexist with superconductivity, which makes the system a promising platform for exploring Majorana Fermions.

Majorana Zero Mode Detected with Spin Selective Andreev Reflection in the Vortex of a Topological Superconductor.

Recently, theory has predicted a Majorana zero mode (MZM) to induce spin selective Andreev reflection (SSAR), a novel magnetic property which can be used to detect the MZM. Here, spin-polarized scanning tunneling microscopy or spectroscopy has been applied to probe SSAR of MZMs in a topological superconductor of the Bi_{2}Te_{3}/NbSe_{2} heterostructure. The zero-bias peak of the tunneling differential conductance at the vortex center is observed substantially higher when the tip polarization and the external magnetic field are parallel rather than antiparallel to each other. This spin dependent tunneling effect provides direct evidence of MZM and reveals its magnetic property in addition to the zero energy modes. Our work will stimulate MZM research on these novel physical properties and, hence, is a step towards experimental study of their statistics and application in quantum computing.

Identifying the Assembly Configuration and Fluorescence Spectra of Nanoscale Zinc-Tetraphenylporphyrin Aggregates with Scanning Tunneling Microscopy.

ZnTPP (Zinc-Tetraphenylporphyrin) is one of the most common nanostructured materials, having high stability and excellent optoelectronic properties. In this paper, the fluorescence features of self-assembled ZnTPP monomers and aggregates on Au(111) surface are investigated in detail on the nanometer scale with scanning tunneling microscopy (STM). The formation of ZnTPP dimers is found in thick layers of a layer-by-layer molecular assembly on Au substrate with its specific molecular arrangement well characterized. Tip-induced luminescence shows a red shift from tilted dimers comparing with the behavior from monomers, which can be attributed to the change of vibrational states due to the intermolecular interaction and the increasing dielectric effect. The nanoscale configuration dependence of electroluminescence is demonstrated to provide a powerful tool aiding the design of functional molecular photoelectric devices.

Epitaxial growth of two-dimensional stanene.

Following the first experimental realization of graphene, other ultrathin materials with unprecedented electronic properties have been explored, with particular attention given to the heavy group-IV elements Si, Ge and Sn. Two-dimensional buckled Si-based silicene has been recently realized by molecular beam epitaxy growth, whereas Ge-based germanene was obtained by molecular beam epitaxy and mechanical exfoliation. However, the synthesis of Sn-based stanene has proved challenging so far. Here, we report the successful fabrication of 2D stanene by molecular beam epitaxy, confirmed by atomic and electronic characterization using scanning tunnelling microscopy and angle-resolved photoemission spectroscopy, in combination with first-principles calculations. The synthesis of stanene and its derivatives will stimulate further experimental investigation of their theoretically predicted properties, such as a 2D topological insulating behaviour with a very large bandgap, and the capability to support enhanced thermoelectric performance, topological superconductivity and the near-room-temperature quantum anomalous Hall effect.

Development of micro-four-point probe in a scanning tunneling microscope for in situ electrical transport measurement.

Electrons at surface may behave differently from those in bulk of a material. Multi-functional tools are essential in comprehensive studies on a crystal surface. Here, we developed an in situ microscopic four-point probe (4PP) transport measurement system on the basis of a scanning tunneling microscope (STM). In particular, convenient replacement between STM tips and micro-4PPs enables systematic investigations of surface morphology, electronic structure, and electrical transport property of a same sample surface. Performances of the instrument are demonstrated with high-quality STM images, tunneling spectra, and low-noise electrical I-V characteristic curves of a single-layer FeSe film grown on a conductive SrTiO3 surface.

Experimental detection of a Majorana mode in the core of a magnetic vortex inside a topological insulator-superconductor Bi(2)Te(3)/NbSe(2) heterostructure.

Majorana fermions have been intensively studied in recent years for their importance to both fundamental science and potential applications in topological quantum computing. They are predicted to exist in a vortex core of superconducting topological insulators. However, it is extremely difficult to distinguish them experimentally from other quasiparticle states for the tiny energy difference between Majorana fermions and these states, which is beyond the energy resolution of most available techniques. Here, we circumvent the problem by systematically investigating the spatial profile of the Majorana mode and the bound quasiparticle states within a vortex in Bi(2)Te(3) films grown on a superconductor NbSe(2). While the zero bias peak in local conductance splits right off the vortex center in conventional superconductors, it splits off at a finite distance ∼20 nm away from the vortex center in Bi(2)Te(3). This unusual splitting behavior has never been observed before and could be possibly due to the Majorana fermion zero mode. While the Majorana mode is destroyed by the interaction between vortices, the zero bias peak splits as a conventional superconductor again. This work provides self-consistent evidences of Majorana fermions and also suggests a possible route to manipulating them.

Superconductivity above 100 K in single-layer FeSe films on doped SrTiO3.

Recent experiments on FeSe films grown on SrTiO3 (STO) suggest that interface effects can be used as a means to reach superconducting critical temperatures (Tc) of up to 80 K (ref. ). This is nearly ten times the Tc of bulk FeSe and higher than the record value of 56 K for known bulk Fe-based superconductors. Together with recent studies of superconductivity at oxide heterostructure interfaces, these results rekindle the long-standing idea that electron pairing at interfaces between two different materials can be tailored to achieve high-temperature superconductivity. Subsequent angle-resolved photoemission spectroscopy measurements of the FeSe/STO system revealed an electronic structure distinct from bulk FeSe (refs , ), with an energy gap vanishing at around 65 K. However, ex situ electrical transport measurements have so far detected zero resistance-the key experimental signature of superconductivity-only below 30 K. Here, we report the observation of superconductivity with Tc above 100 K in the FeSe/STO system by means of in situ four-point probe electrical transport measurements. This finding confirms FeSe/STO as an ideal material for studying high-Tc superconductivity.

Effect of yessotoxin on cytosolic calcium levels in human hepatocellular carcinoma cells in vitro.

Yessotoxin (YTX) and its analogs are a type of marine toxins found in marine environments in numerous coastal countries. These toxins tend to accumulate in filter-feeding molluscs and may threaten the shellfish industry and public health. Several previous studies indicated that YTX may induce apoptosis in different types of cell lines, although the exact underlying mechanisms have not yet been elucidated. The aim of this study was to mainly focus on the effect of YTX on cytosolic Ca2+ levels in human hepatocellular carcinoma cells. In order to investigate the exact mechanism of YTX-evoked Ca2+ increase, laser scanning confocal microscopy was used, with the addition of the chelator ethylene glycol tetraacetic acid (EGTA) and nifedipine, an L-type Ca2+ channel blocker, to the reaction system. The results demonstrated that YTX caused cytosolic Ca2+ level increase in Bel7402 cells and the YTX-evoked Ca2+ increase was successfully blocked by EGTA and nifedipine. Therefore, our results indicated that YTX may cause apoptosis via inducing Ca2+ entry in Bel7402 cells.

Yessotoxin induces apoptosis in HL7702 human liver cells.

The marine toxin yessotoxin (YTX) is found in numerous aquatic environments and poses a potential threat to the shellfish industry and to public health. We analyzed the toxicity of YTX on HL7702 human liver cells using optical microscopy, Hoechst 33342 chromatin staining, DNA gel electrophoresis, rhodamine 123 staining and calcium-sensitive laser scanning confocal microscopy. The results demonstrated that YTX induced the usual hallmarks of apoptosis, including chromatin condensation, DNA laddering, activity of caspase-3 deregulation and loss of mitochondrial membrane potential. Furthermore, YTX caused cytosolic calcium levels to increase in HL7702 cells. YTX may cause liver damage through hepatocyte apoptosis.

Characterization of apoptotic changes induced by yessotoxin in the Bel7402 human hepatoma cell line.

The apoptotic effects of yessotoxin (YTX) on Bel7402 human hepatoma cells have been evaluated by the combination of several methods, including optical microscopy, Hoechst 33342 staining and DNA gel electrophoresis. Rhodamine 123 staining has also been used to investigate changes in mitochondrial transmembrane potential. The results indicated that YTX has negative effects on human liver cells and induces apoptosis. Furthermore, changes in calcium concentrations were analyzed using the fluorescence probe Fluo-3 AM. The results showed that intracellular calcium concentrations increased after treatment with YTX.

Apoptosis induced by yessotoxins in Hela human cervical cancer cells in vitro.

To investigate the apoptotic effects of an extract of red-tide algae, Protoceratium reticulatum, on HeLa cells, we used liquid chromatography-tandem mass spectrometry, optical microscopy, Hoechst 33342/propidine iodide staining, and DNA gel electrophoresis to analyze its constituents and toxicity, as well as rhodamine 123 staining to investigate changes in mitochondrial membrane potential. Analysis showed that the P. reticulatum extract contained the yessotoxins (YTXs) homo-YTX, 45-OH-YTX and 45-OH-homo-YTX. The results indicated that P. reticulatum extract negatively influences HeLa cells and induces their apoptosis.