Highly Tunable Charge-Spin Conversion in Topological Insulator Cr0.08-(Bi0.37Sb0.63)1.92Te3 via Ferroelectric Polarization.

Topological insulators possess strong spin-orbit coupling, which potentially presents efficient charge-spin interconversion. The effective manipulation of this conversion plays a central role in spin-based device applications and is attracting increasing attention nowadays. In this study, by constructing a multifunctional hybrid device Cr-BST/Py/PMN-PT and applying spin-torque ferromagnetic resonance measurement, continuously controllable charge-spin conversion efficiency and even the enhancement of its value up to about 450% are realized via regulation of the ferroelectric polarization in the topological insulator Cr-BST. The band structure of Cr-BST characterized by angle-resolved photoelectron spectroscopy measurement presents an apparent Dirac-like state located at the large band gap of the bulk state near the Fermi level, which indicates a surface state-dominated contribution to the charge-spin conversion. Further investigation via density functional theory on the electronic structure of BST verifies that the controllable conversion efficiency dominantly originates from the evolution of the band structure under strain modulation. These findings demonstrate TIs as one of the promising materials for the charge-spin interconversion and its regulation, which are instructive for low-dissipation spintronics devices.

Application of machine learning in the diagnosis of gastric cancer based on noninvasive characteristics.

BACKGROUND: The diagnosis of gastric cancer mainly relies on endoscopy, which is invasive and costly. The aim of this study is to develop a predictive model for the diagnosis of gastric cancer based on noninvasive characteristics. AIMS: To construct a predictive model for the diagnosis of gastric cancer with high accuracy based on noninvasive characteristics. METHODS: A retrospective study of 709 patients at Zhejiang Provincial People's Hospital was conducted. Variables of age, gender, blood cell count, liver function, kidney function, blood lipids, tumor markers and pathological results were analyzed. We used gradient boosting decision tree (GBDT), a type of machine learning method, to construct a predictive model for the diagnosis of gastric cancer and evaluate the accuracy of the model. RESULTS: Of the 709 patients, 398 were diagnosed with gastric cancer; 311 were health people or diagnosed with benign gastric disease. Multivariate analysis showed that gender, age, neutrophil lymphocyte ratio, hemoglobin, albumin, carcinoembryonic antigen (CEA), carbohydrate antigen 125 (CA125) and carbohydrate antigen 199 (CA199) were independent characteristics associated with gastric cancer. We constructed a predictive model using GBDT, and the area under the receiver operating characteristic curve (AUC) of the model was 91%. For the test dataset, sensitivity was 87.0% and specificity 84.1% at the optimal threshold value of 0.56. The overall accuracy was 83.0%. Positive and negative predictive values were 83.0% and 87.8%, respectively. CONCLUSION: We construct a predictive model to diagnose gastric cancer with high sensitivity and specificity. The model is noninvasive and may reduce the medical cost.

Chiral fermion reversal in chiral crystals.

In materials chiral fermions such as Weyl fermions are characterized by nonzero chiral charges, which are singular points of Berry curvature in momentum space. Recently, new types of chiral fermions beyond Weyl fermions have been discovered in structurally chiral crystals CoSi, RhSi and PtAl. Here, we have synthesized RhSn single crystals, which have opposite structural chirality to the CoSi crystals we previously studied. Using angle-resolved photoemission spectroscopy, we show that the bulk electronic structures of RhSn are consistent with the band calculations and observe evident surface Fermi arcs and helical surface bands, confirming the existence of chiral fermions in RhSn. It is noteworthy that the helical surface bands of the RhSn and CoSi crystals have opposite handedness, meaning that the chiral fermions are reversed in the crystals of opposite structural chirality. Our discovery establishes a direct connection between chiral fermions in momentum space and chiral lattices in real space.

Experimental evidence of anomalously large superconducting gap on topological surface state of ß-Bi2Pd film.

Connate topological superconductor (TSC) combines topological surface states with nodeless superconductivity in a single material, achieving effective p-wave pairing without interface complication. By combining angle-resolved photoemission spectroscopy and in-situ molecular beam epitaxy, we studied the momentum-resolved superconductivity in ß-Bi2Pd film. We found that the superconducting gap of topological surface state (ΔTSS ∼ 3.8 meV) is anomalously enhanced from its bulk value (Δb ∼ 0.8 meV). The ratio of 2ΔTSS/kBTc ∼ 16.3, is substantially larger than the BCS value. By measuring ß-Bi2Pd bulk single crystal as a comparison, we clearly observed the upward-shift of chemical potential in the film. In addition, a concomitant increasing of surface weight on the topological surface state was revealed by our first principle calculation, suggesting that the Dirac-fermion-mediated parity mixing may cause this anomalous superconducting enhancement. Our results establish ß-Bi2Pd film as a unique case of connate TSCs with a highly enhanced topological superconducting gap, which may stabilize Majorana zero modes at a higher temperature.

A Mott insulator continuously connected to iron pnictide superconductors.

Iron-based superconductivity develops near an antiferromagnetic order and out of a bad-metal normal state, which has been interpreted as originating from a proximate Mott transition. Whether an actual Mott insulator can be realized in the phase diagram of the iron pnictides remains an open question. Here we use transport, transmission electron microscopy, X-ray absorption spectroscopy, resonant inelastic X-ray scattering and neutron scattering to demonstrate that NaFe1-xCuxAs near x≈0.5 exhibits real space Fe and Cu ordering, and are antiferromagnetic insulators with the insulating behaviour persisting above the Néel temperature, indicative of a Mott insulator. On decreasing x from 0.5, the antiferromagnetic-ordered moment continuously decreases, yielding to superconductivity ∼x=0.05. Our discovery of a Mott-insulating state in NaFe1-xCuxAs thus makes it the only known Fe-based material, in which superconductivity can be smoothly connected to the Mott-insulating state, highlighting the important role of electron correlations in the high-Tc superconductivity.

Persistent high-energy spin excitations in iron-pnictide superconductors.

Motivated by the premise that superconductivity in iron-based superconductors is unconventional and mediated by spin fluctuations, an intense research effort has been focused on characterizing the spin-excitation spectrum in the magnetically ordered parent phases of the Fe pnictides and chalcogenides. For these undoped materials, it is well established that the spin-excitation spectrum consists of sharp, highly dispersive magnons. The fate of these high-energy magnetic modes upon sizable doping with holes is hitherto unresolved. Here we demonstrate, using resonant inelastic X-ray scattering, that optimally hole-doped superconducting Ba(0.6)K(0.4)Fe(2)As(2) retains well-defined, dispersive high-energy modes of magnetic origin. These paramagnon modes are softer than, though as intense as, the magnons of undoped antiferromagnetic BaFe(2)As(2). The persistence of spin excitations well into the superconducting phase suggests that the spin fluctuations in Fe-pnictide superconductors originate from a distinctly correlated spin state. This connects Fe pnictides to cuprates, for which, in spite of fundamental electronic structure differences, similar paramagnons are present.