Observation of a Ubiquitous(π,π)-Type Nematic Superconducting Order in the Whole Superconducting Dome of Ultra-Thin BaFe_(2-x)Ni_(x)As_(2) Single Crystals

In iron-based superconductors,the(0,π) or(π,0) nematicity,which describes an electronic anisotropy with a fourfold symmetry breaking,is well established and believed to be important for understanding the superconducting mechanism.However,how exactly such a nematic order observed in the normal state can be related to the superconducting pairing is still elusive.Here,by performing angular-dependent in-plane magnetoresistivity using ultra-thin flakes in the steep superconducting transition region,we unveil a nematic superconducting order along the(π,π) direction in electron-doped BaFe_(2-x)Ni_(x)As_(2) from under-doped to heavily overdoped regimes with x=0.065- 0.18.It shows superconducting gap maxima along the(π,π) direction rotated by 45° from the nematicity along(0, π) or(π,0) direction observed in the normal state.A similar(π,π)-type nematicity is also observed in the under-doped and optimally doped hole-type Ba1-yKyFe2 As_(2),with y=0.2-0.5.These results suggest that the(π,π) nematic superconducting order is a universal feature that needs to be taken into account in the superconducting pairing mechanism in iron-based superconductors.

The study of magnetic topological semimetals by first principles calculations

Magnetic topological semimetals(TSMs)are topological quantum materials with broken time-reversal symmetry(TRS)and isolated nodal points or lines near the Fermi level.Their topological properties would typically reveal from the bulk-edge correspondence principle as nontrivial surface states such as Fermi arcs or drumhead states,etc.Depending on the degeneracies and distribution of the nodes in the crystal momentum space,TSMs are usually classified into Weyl semimetals(WSMs),Dirac semimetals(DSMs),nodal-line semimetals(NLSMs),triple-point semimetals(TPSMs),etc.In this review article,we present the recent advances of magnetic TSMs from a computational perspective.We first review the early predicted magnetic WSMs such as pyrochlore iridates and HgCr_(2)Se_(4),as well as the recently proposed Heusler,Kagome layers,and honeycomb lattice WSMs.Then we discuss the recent developments of magnetic DSMs,especially CuMnAs in Type-III and EuCd_(2)As_(2) in Type-IV magnetic space groups(MSGs).Then we introduce some magnetic NLSMs that are robust against spin–orbit coupling(SOC),namely Fe_(3)GeTe_(2) and LaCl(LaBr).Finally,we discuss the prospects of magnetic TSMs and the interesting directions for future research.

Three factors make bulk high-entropy alloys as effective electrocatalysts for oxygen evolution

Even in their bulk forms,complex alloys like high-entropy alloys(HEAs)exhibit favorable activity and stability as electrocatalysts for the oxygen evolution reaction(OER).However,the underlying reasons are not yet fully understood.In a family of Mo-doped CrFeCoNi-based HEAs,we have identified three crucial factors that govern their performance:(i)homogeneous solid solution phase of HEAs helps to maintain high-valence states of metals;(ii)surface reconstruction results in a hybrid material comprising amorphous domains and percolated crystalline structures;(iii)diversity of active intermediate species(M–O,M–OOH,and,notably,the abundance of superoxideμ–OO),which display stronger adsorption capacity on the reconstructed surface.These results are revealing due to their resemblance to findings in other families of electrocatalysts for OER,as well as their unique features specific to HEAs.In line with these factors,a CrFeCoNiMo0.2 bulk integrated electrode displays a low overpotential of 215 mV,rapid kinetics,and long-term stability of over 90 d.Bulk HEAs hold great potential for industrial applications.

Fragile topological band in the checkerboard antiferromagnetic monolayer FeSe

By means of the first-principles calculations and magnetic topological quantum chemistry,we demonstrate that the low-energy physics in the checkerboard antiferromagnetic(AFM)monolayer FeSe,very close to an AFM topological insulator that hosts robust edge states,can be well captured by a double-degenerate nearly flat band with fragile topology just below the Fermi level.The Wilson loop calculations identify that such fragile topology is protected by the S_(4z) symmetry,which gives rise to a 2D second-order topological insulator that supports the bound state with fractional charge e/2 at the sample corner.This work provides a platform to study the intriguing properties of magnetic fragile topological electronic states.Previous observations of the edge states and bound states in checkerboard AFM monolayer FeSe can also be well understood in our work.

Manipulation of Molecular Qubits by Isotope Effect on Spin Dynamics

Controlling spin behavior via external stimuli is a key route to develop molecular spintronics devices.Photons,temperature,pressure,chemicals,and electric field are the possible stimuli.Herein,we report a new method,the isotope effect,to control spin behavior in molecule magnet systems.It can not only control the relaxation of magnetization,but also regulate the spin lifetime of quantum coherence.

Topological superconductor candidates PdBi_(2)Te_(4) and PdBi_(2)Te_(5) from a generic ab initio strategy

Superconducting topological metals(SCTMs)have recently emerged as a promising platform of topological superconductivity(TSC)and Majorana zero modes for quantum computation.Despite their importance in both fundamental research and applications,SCTMs are very rare in nature.Here,we propose a strategy to design SCTMs by intercalating the superconducting units into the topological insulators.A program that characterizes the superconducting BdG Chern number of 2D BdG Hamiltonian from ab initio calculations is also developed.Following this strategy,PdBi_(2)Te_(5) and PdBi_(2)Te_(4) are found to be experimentally synthesizable and ideal SCTMs.Chiral TSC could be realized in such SCTMs by incorporating topological surface states with Zeeman effect,which can be realized by an external magnetic field or in proximity to ferromagnetic insulator.Our strategy provides a new method for identifying the SCTMs and TSC candidates,and the program makes it possible to design and modulate the TSC candidates from ab initio calculations.