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Exotic chiral fermions beyond Weyl fermions have recently been discovered in a series of chiral crystals such as CoSi. Here, the authors report the evidences of chiral fermions in RhSn with opposite handedness compared to those observed in CoSi, where the structural chirality is also opposite.

BackgroundThe 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.AimsTo construct a predictive model for the diagnosis of gastric cancer with high accuracy based on noninvasive characteristics.MethodsA 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.ResultsOf 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.ConclusionWe construct a predictive model to diagnose gastric cancer with high sensitivity and specificity. The model is noninvasive and may reduce the medical cost.

Whether an actual Mott insulator phase exists in iron pnictides remains elusive. Here, Songet al. demonstrate an antiferromagnetic insulator phase persisting above the Néel temperature in NaFe1−xCuxAs, indicative of a Mott insulator, highlighting the role of electron correlations in high-Tcsuperconductivity.

The interplay between time-reversal symmetry (TRS) and band topology plays a crucial role in topological states of quantum matter. In time-reversal-invariant (TRI) systems, the inversion of spin-degenerate bands with opposite parity leads to nontrivial topological states, such as topological insulators and Dirac semimetals. When the TRS is broken, the exchange field induces spin splitting of the bands. The inversion of a pair of spin-splitting subbands can generate more exotic topological states, such as quantum anomalous Hall insulators and magnetic Weyl semimetals. So far, such topological phase transitions driven by the TRS breaking have not been visualized. In this work, using angle-resolved photoemission spectroscopy, we have demonstrated that the TRS breaking induces a band inversion of a pair of spin-splitting subbands at the TRI points of Brillouin zone in EuB_{6}, when a long-range ferromagnetic order is developed. The dramatic changes in the electronic structure result in a topological phase transition from a TRI ordinary insulator state to a TRS-broken topological semimetal (TSM) state. Remarkably, the magnetic TSM state has an ideal electronic structure, in which the band crossings are located at the Fermi level without any interference from other bands. Our findings not only reveal the topological phase transition driven by the TRS breaking, but also provide an excellent platform to explore novel physical behavior in the magnetic topological states of quantum matter.

In magnetic topological insulators (TIs), the interplay between magnetic order and nontrivial topology can induce fascinating topological quantum phenomena, such as the quantum anomalous Hall effect, chiral Majorana fermions, and axion electrodynamics. Recently, a great deal of attention has been focused on the intrinsic magnetic TIs, where disorder effects can be eliminated to a large extent, which is expected to facilitate the emergence of topological quantum phenomena. Despite intensive efforts, experimental evidence of the topological surface states (SSs) remains elusive. Here, by combining first-principles calculations and angle-resolved photoemission spectroscopy (ARPES) experiments, we reveal that EuSn_{2}As_{2} is an antiferromagnetic TI with the observation of Dirac SSs consistent with our prediction. We also observe nearly gapless Dirac SSs in antiferromagnetic TIs MnBi_{2n}Te_{3n+1} (n=1 and 2), which are absent in previous ARPES results. These results provide clear evidence for nontrivial topology of these intrinsic magnetic TIs. Furthermore, we find that the topological SSs show no observable changes across the magnetic transition within the experimental resolution, indicating that the magnetic order has a quite small effect on the topological SSs, which can be attributed to weak hybridization between the localized magnetic moments, from either 4f or 3d orbitals, and the topological electronic states. This finding provides insights for further research that the correlations between magnetism and topological states need to be strengthened to induce larger gaps in the topological SSs, which will facilitate the realization of topological quantum phenomena at higher temperatures.

Topological Dirac semimetals (DSMs) present a kind of topologically nontrivial quantum state of matter, which has massless Dirac fermions in the bulk and topologically protected states on certain surfaces. In superconducting DSMs, the effects of their nontrivial topology on superconducting pairing could realize topological superconductivity in the bulk or on the surface. As superconducting pairing takes place at the Fermi level EF, to make the effects possible, the Dirac points should lie in the vicinity of EF so that the topological electronic states can participate in the superconducting paring. Here, we show using angle-resolved photoelectron spectroscopy that in a series of (Ir1−xPtx)Te2 compounds, the type-II Dirac points reside around EF in the superconducting region, in which the bulk superconductivity has a maximum Tc of ∼ 3 K. The realization of the coexistence of bulk superconductivity and low-energy Dirac fermions in (Ir1−xPtx)Te2 paves the way for studying the effects of the nontrivial topology in DSMs on the superconducting state. [ABSTRACT FROM AUTHOR]

The electronic structure of iron-pnictide compound superconductor Ba2Ti2Fe2As4O, which has metallic intermediate Ti2O layers, is studied using angle-resolved photoemission spectroscopy. The Ti-related bands show a ‘peak-dip-hump’ line shape with two branches of dispersion associated with the polaronic states at temperatures below around 120 K. This change in the spectra occurs along with the resistivity anomaly that was not clearly understood in a previous study. Moreover, an energy gap induced by the superconducting proximity effect opens in the polaronic bands at temperatures below T c (∼21 K). Our study provides the spectroscopic evidence that superconductivity coexists with polarons in the same bands near the Fermi level, which provides a suitable platform to study interactions between charge, lattice and spin freedoms in a correlated system. [ABSTRACT FROM AUTHOR]

We report an angle-resolved photoemission investigation of optimally doped Ca0.33Na0.67Fe2As2. The Fermi surface topology of this compound is similar to that of the well-studied Ba0.6K0.4Fe2As2 material, except for larger hole pockets resulting from a higher hole concentration per Fe atoms. We find that the quasi-nesting conditions are weakened in this compound compared to Ba0.6K0.4Fe2As2. Similar to Ba0.6K0.4Fe2As2, we observe nearly isotropic superconducting gaps with Fermi surface-dependent magnitudes for Ca0.33Na0.67Fe2As2. A small variation in the gap size along the momentum direction perpendicular to the surface is found for one of the Fermi surfaces. Our superconducting gap results on all Fermi surface sheets fit simultaneously very well to a global gap function derived from a strong coupling approach, which contains only 2 global parameters. [ABSTRACT FROM AUTHOR]

Electronic spin and orbital (dd) excitation spectra of (CaxLa1-x)(Ba1.75-xLa0.25+x)Cu3Oy samples are measured by resonant inelastic x-ray scattering (RIXS). In this compound, Tc of samples with identical hole dopings is strongly affected by the Ca/Ba substitution x due to subtle variations in the lattice constants, while crystal symmetry and disorder as measured by linewidths are x independent. We examine two extreme values of x and two extreme values of hole-doping content y corresponding to antiferromagnetic and superconducting states. The x dependence of the spin-mode energies is approximately the same for both the antiferromagnetic and superconducting samples. This clearly demonstrates that RIXS is sensitive to the superexchange J even in doped samples. A positive correlation between J and the maximum of Tc at optimal doping (Tcmax) is observed. We also measured the x dependence of the dxy → dx2-y2 and dxz/yz → dx2-y2 orbital splittings. We infer that the effect of the unresolved d3z2-r2 → dx2→y2 excitation on Tcmax is much smaller than the effect of J . There appears to be dispersion in the dxy → dx2-y2 peak of up to 0.05 eV. Our fitting furthermore indicates an asymmetric dispersion for the dxz/yz → dx2-y2 excitation. A peak at ~0.8 eV is also observed and attributed to a dd excitation in the chain layer. [ABSTRACT FROM AUTHOR]