Suppression of Superconductivity by Twin Boundaries in FeSe

Low-temperature scanning tunneling microscopy and spectroscopy are employed to investigate twin boundaries in stoichiometric FeSe films grown by molecular beam epitaxy. Twin boundaries can be unambiguously identified by imaging the 90{\deg} change in the orientation of local electronic dimers from Fe site impurities on either side. Twin boundaries run at approximately 45{\deg} to the Fe-Fe bond directions, and noticeably suppress the superconducting gap, in contrast with the recent experimental and theoretical findings in other iron pnictides. Furthermore, vortices appear to accumulate on twin boundaries, consistent with the degraded superconductivity there. The variation in superconductivity is likely caused by the increased Se height in the vicinity of twin boundaries, providing the first local evidence for the importance of this height to the mechanism of superconductivity.Comment: 6 pages, 7 figure

Power-Law Decay of Standing Waves on the Surface of Topological Insulators

We propose a general theory on the standing waves (quasiparticle interference pattern) caused by the scattering of surface states off step edges in topological insulators, in which the extremal points on the constant energy contour of surface band play the dominant role. Experimentally we image the interference patterns on both Bi$_2$Te$_3$ and Bi$_2$Se$_3$ films by measuring the local density of states using a scanning tunneling microscope. The observed decay indices of the standing waves agree excellently with the theoretical prediction: In Bi$_2$Se$_3$, only a single decay index of -3/2 exists; while in Bi$_2$Te$_3$ with strongly warped surface band, it varies from -3/2 to -1/2 and finally to -1 as the energy increases. The -1/2 decay indicates that the suppression of backscattering due to time-reversal symmetry does not necessarily lead to a spatial decay rate faster than that in the conventional two-dimensional electron system. Our formalism can also explain the characteristic scattering wave vectors of the standing wave caused by non-magnetic impurities on Bi$_2$Te$_3$.Comment: 4 pages, 3 figure

A new lithophilous species of Gesneriaceae, Petrocodon rubrostriatus, from the karst area of South Yunnan, China

A new lithophytic species of Gesneriaceae, Petrocodon rubrostriatus K.Tan, X.Q.Song & M.X.Ren, sp. nov. from Lvchun County, South Yunnan, China, is described and illustrated here. It closest resembles P. mollifolius (W.T.Wang) A.Weber & Mich.Möller, but the new species is differentiated from it by red to brownish-red stripes in the yellow corolla throat and 4.5 mm long bract lobes, a ca. 10 mm long style, and staminodes inserted at 2.5–3 mm from the corolla base. The species is preliminarily assessed as ‘Critically Endangered’ (CR) according to IUCN criteria, since currently only one single locality is known with a few subpopulations on a fragmented limestone cliff, with fewer than 300 individuals

Visualizing the elongated vortices in γ\gamma-Ga nanostrips

We study the magnetic response of superconducting $\gamma$-Ga via low temperature scanning tunneling microscopy and spectroscopy. The magnetic vortex cores rely substantially on the Ga geometry, and exhibit an unexpectedly-large axial elongation with aspect ratio up to 40 in rectangular Ga nano-strips (width $l$ $<$ 100 nm). This is in stark contrast with the isotropic circular vortex core in a larger round-shaped Ga island. We suggest that the unusual elongated vortices in Ga nanostrips originate from geometric confinement effect probably via the strong repulsive interaction between the vortices and Meissner screening currents at the sample edge. Our finding provides novel conceptual insights into the geometrical confinement effect on magnetic vortices and forms the basis for the technological applications of superconductors.Comment: published in Phys. Rev. B as a Rapid Communicatio

Shelf Life Prediction of UHT Milk Packaging Based on BP Neural Network

To investigate the effects of initial protein, fat content, and storage temperature on the shelf life of UHT pure milk packaging, three types of UHT pure milk were used as research objects to experimentally measure sample browning index and protein hydrolysis index during storage at 23, 30, and 37 ℃. Integrate the dataset and determine specific input parameters based on its performance on the prediction set, and carry out UHT pure milk packaging shelf life prediction based on BP neural network. The results showed that the fitting degrees of the BP neural network model for the browning index and protein hydrolysis index of UHT milk were 0.9412 and 0.9527, respectively, and compared with traditional multiple linear regression model’s number of 0.8799 and 0.9211, the BP neural network model with optimized hidden layer neuron numbers had higher prediction accuracy for the changes in characteristic indicators during the storage period of UHT pure milk, providing technical support for rapid and accurate prediction of the shelf life of UHT pure milk with different formulas

Evaluation of Changes in the Characteristic Flavor of Ultra-high Temperature Sterilized Milk under the Effects of Temperature and Light

In order to study changes in the characteristic flavor of ultra-high temperature sterilized (UHT) milk under the influence of storage temperature and light, headspace solid phase microextraction (SPME) combined with gas chromatography-mass spectrometry (GC-MS) was used to detect the volatile flavor components of the product. Descriptive sensory evaluation, orthogonal partial least squares-discriminant analysis (OPLS-DA) and entropy weight method were used to determine the relationship between major characteristic flavors and characteristic substances. The effects of temperature and light flux on the flavor changes of different formulations of UHT milk were analyzed, and a model for comprehensive analysis of the characteristic flavors of UHT milk was developed based on the effects of initial unsaturated fatty acid content, temperature and light flux. The results of this research provide support for the quality control of different formulations of UHT milk

Interface induced high temperature superconductivity in single unit-cell FeSe films on SrTiO3

Searching for superconducting materials with high transition temperature (TC) is one of the most exciting and challenging fields in physics and materials science. Although superconductivity has been discovered for more than 100 years, the copper oxides are so far the only materials with TC above 77 K, the liquid nitrogen boiling point. Here we report an interface engineering method for dramatically raising the TC of superconducting films. We find that one unit-cell (UC) thick films of FeSe grown on SrTiO3 (STO) substrates by molecular beam epitaxy (MBE) show signatures of superconducting transition above 50 K by transport measurement. A superconducting gap as large as 20 meV of the 1 UC films observed by scanning tunneling microcopy (STM) suggests that the superconductivity could occur above 77 K. The occurrence of superconductivity is further supported by the presence of superconducting vortices under magnetic field. Our work not only demonstrates a powerful way for finding new superconductors and for raising TC, but also provides a well-defined platform for systematic study of the mechanism of unconventional superconductivity by using different superconducting materials and substrates