Superconducting Properties and Absence of Time Reversal Symmetry Breaking in the Noncentrosymmetric Superconducting Compounds Ta_(x)Re_(1-x)(0.1≤x≤0.25)

Unconventional superconductivity,in particular,in noncentrosymmetric systems,has been a long-sought topic in condensed matter physics.Recently,Re-based superconductors have attracted great attention owing to the potential time-reversal symmetry breaking in their superconducting states.We report the superconducting properties of noncentrosymmetric compounds Ta_(x)Re_(1-x) with 0.1 ≤x≤0.25,and find that the superconducting transition temperature reaches a maximum of ~8 K at the optimal level x=0.15.Nevertheless,muon-spin rotation and relaxation measurements reveal no time-reversal symmetry breaking existing in its superconducting state,which is in sharp contrast to both centrosymmetric Re metal and many other noncentrosymmetric Re-based superconductors.

Negative Magnetoresistance in Antiferromagnetic Topological Insulator EuSn2As2

The measurements of magnetization,longitudinal and Hall resistivities are carried out on the intrinsic antiferromagnetic(AFM) topological insulator ElSn2 As2.It is confirmed that our ElSn2 As2 crystal is a heavily hole doping A-type AFM metal with the Neel temperature TN=24 K,with a metamagnetic transition from an AFM to a ferromagnetic(FIM) phase occurring at a certain critical magnetic Held for the different Held orientations.Meanwhile,we also find that the carrier concentration does not change with the evolution of magnetic order,indicating that the weak interaction between the localized magnetic moments from Eu2+4f7 orbits and the electronic states near the Fermi level.Although the quantum anomalous Hall effect(AHE) is not observed in our crystals,it is found that a relatively large negative magnetoresistance (-13%) emerges in the AFM phase,and exhibits an exponential dependence upon magnetic Held,whose microscopic origin is waiting to be clarified in future research.

Ab initio molecular dynamics and materials design for embedded phase-change memory

The Ge_(2)Sb_(2)Te_(5)alloy has served as the core material in phase-change memories with high switching speed and persistent storage capability at room temperature.However widely used,this composition is not suitable for embedded memories—for example,for automotive applications,which require very high working temperatures above 300℃.Ge–Sb–Te alloys with higher Ge content,most prominently Ge2Sb1Te2(‘212’),have been studied as suitable alternatives,but their atomic structures and structure–property relationships have remained widely unexplored.Here,we report comprehensive first-principles simulations that give insight into those emerging materials,located on the compositional tie-line between Ge_(2)Sb_(1)Te_(2) and elemental Ge,allowing for a direct comparison with the established Ge_(2)Sb_(2)Te_(5)material.Electronic-structure computations and smooth overlap of atomic positions(SOAP)similarity analyses explain the role of excess Ge content in the amorphous phases.Together with energetic analyses,a compositional threshold is identified for the viability of a homogeneous amorphous phase(‘zero bit’),which is required for memory applications.Based on the acquired knowledge at the atomic scale,we provide a materials design strategy for high-performance embedded phase-change memories with balanced speed and stability,as well as potentially good cycling capability.