查看更多>>摘要：Uniaxial strain is a powerful tuning parameter that can control symmetry and anisotropic electronic properties in iron-based superconductors.However,accurately characterizing anisotropic strain can be challenging and complex.Here,we utilize a cryogenic optical system equipped with a high-spatial-resolution microscope to characterize surface strains in iron-based superconductors using the digital image correlation method.Compared with other methods such as high-resolution x-ray diffraction,strain gauge,and capacitive sensor,digital image correlation offers a non-contact full-field measurement approach,acting as an optical virtual strain gauge that provides high spatial resolution.The results measured on detwinned BaFe2As2 are quantitatively consistent with the distortion measured by x-ray diffraction and neutron Larmor diffraction.These findings highlight the potential of cryogenic digital image correlation as an effective and accessible tool for probing the isotropic and anisotropic strains,facilitating applications of uniaxial strain tuning in research of quantum materials.
查看更多>>摘要：SrIrO3,a Dirac material with a strong spin-orbit coupling(SOC),is a platform for studying topological properties in strongly correlated systems,where its band structure can be modulated by multiple factors,such as crystal symmetry,elements doping,oxygen vacancies,magnetic field,and temperature.Here,we find that the engineered carrier density plays a critical role on the magnetoelectric transport properties of the topological semimetal SrIrO3.The decrease of carrier density subdues the weak localization and the associated negative magnetoresistance,while enhancing the SOC-induced weak anti-localization.Notably,the sample with the lowest carrier density exhibits high-field positive magnetoresistance,suggesting the presence of a Dirac cone.In addition,the anisotropic magnetoresistance indicates the anisotropy of the electronic structure near the Fermi level.The engineering of carrier density provides a general strategy to control the Fermi surface and electronic structure in topological materials.
查看更多>>摘要：Topological phonon is a new frontier in the field of topological materials.Different from electronic struc-tures,phonons are bosons and most topological phonons are metallic form.Previous studies about topological phonon states were focused on three-dimensional(3D)materials.Owing to the lack of material candidates,two-dimensional(2D)and van der Waals f-electron-related topological phonons were rarely reported.Based on first-principles calculations,we investigate the topological phononic state in the heavy fermion material CeSiI with a layered structure.Both 3D bulk and 2D monolayers have topological nontrivial states in the rarely seen f electron dominated van der Waals metal.Owing to the PT and C3z symmetries,Weyl nodal lines with nonzero Chern numbers exist on the hinge of the Brillouin zone.Protected by C3z rotation symmetry,three pairs of Weyl points with±π Berry phase exist at point K near the frequency of 8 and 10 THz.In addition to the bulk topological charges,corresponding surface/edge states are also systematically analyzed,which gives a consistent understanding.Our results propose another interesting point in the newly discovered rear earth heavy fermion material CeSiI and are helpful for future experimental research of CeSil topological phonons.
查看更多>>摘要：Chemical doping is a critical factor in the development of new superconductors or optimizing the supercon-ducting transition temperature(Tc)of the parent superconducting materials.Here,a new simple urea approach is developed to synthesize the N-doped α-Mo2C.Benefiting from the simple urea method,a broad superconducting dome is found in the Mo2C1-xNx(0 ≤ x ≤ 0.49)compositions.X-ray diffraction results show that the structure of α-Mo2C remains unchanged and there is a variation of lattice parameters with nitrogen doping.Resistiv-ity,magnetic susceptibility,and heat capacity measurement results confirm that Tc was strongly increased from 2.68K(x=0)to 7.05K(x=0.49).First-principles calculations and our analysis indicate that increasing nitro-gen doping leads to a rise in the density of states at the Fermi level and doping-induced phonon softening,which enhances electron-phonon coupling.This results in an increase in Tc and a sharp rise in the upper critical field.Our findings provide a promising strategy for fabricating transition metal carbonitrides and provide a material platform for further study of the superconductivity of transition metal carbides.
查看更多>>摘要：The two-dimensional magnetic van der Waals heterojunctions have opened unprecedented opportunities to explore new physics due to their potential for spintronic applications.Here,combing density functional the-ory with non-equilibrium Green's function technique,we systematically investigate the spin-polarized trans-port properties of Cu/FeX2/h-BN/FeX2/Cu(X=Cl,Br,I)magnetic tunnel junctions(MTJs).It is found that the maximum tunneling magnetoresistance of Cu/FeCl2/h-BN/FeCl2/Cu,Cu/FeBr2/h-BN/FeBr2/Cu,and Cu/FeI2/h-BN/FeI2/Cu MTJs can reach 3443％,3069％,and 1676％,respectively.In the parallel state,the re-sistance area products at zero bias for Cu/FeCl2/h-BN/FeCl2/Cu,Cu/FeBr2/h-BN/FeBr2/Cu,and Cu/FeI2/h-BN/FeI2/Cu MTJs are 0.92,0.47,and 0.32Ω·μm2,respectively.More interestingly,our results indicate that Cu/FeX2/h-BN/FeX2/Cu(X=Cl,Br,I)MTJs can realize spin filtering effect,while Cu/FeCl2/h-BN/FeCl2/Cu and Cu/FeI2/h-BN/FeI2/Cu MTJs exhibit negative differential resistance.Our results demonstrate that large tunneling magnetoresistance,negative differential resistance effect,low resistance area product as well as excellent spin filtering effect coexist in Cu/FeCl2/h-BN/FeCl2/Cu and Cu/FeI2/h-BN/FeI2/Cu MTJs,and that the feasi-ble tunability of such a kind of van der Waals magnetic tunnel junctions is beneficial to designing next-generation logic devices.
查看更多>>摘要：Fe3GaTe2,as a layered ferromagnetic material,has a Curie temperature(Tc)higher than room temperature,making it the key material in next-generation spintronic devices.To be used in practical devices,large-sized high-quality Fe3GaTe2 thin films need to be prepared.Here,the centimeter-scale thin film samples with high crystal quality and above-room-temperature ferromagnetism with strong perpendicular magnetic anisotropy were prepared by molecular beam epitaxy technology.Furthermore,the Tc of the samples raises as the film thickness increases,and reaches 367 K when the film thickness is 60 nm.This study provides material foundations for the new generation of van der Waals spintronic devices and paves the way for the commercial application of Fe3GaTe2.
查看更多>>摘要：Recent experimental and theoretical work has focused on two-dimensional van der Waals(2D vdW)mag-nets due to their potential applications in sensing and spintronics devises.In measurements of these emerging materials,conventional magnetometry often encounters challenges in characterizing the magnetic properties of small-sized vdW materials,especially for antiferromagnets with nearly compensated magnetic moments.Here,we investigate the magnetism of 2D antiferromagnet CrPS4 with a thickness of 8 nm by using dynamic cantilever magnetometry(DCM).Through a combination of DCM experiment and the calculation based on a Stoner-Wohlfarth-type model,we unravel the magnetization states in 2D CrPS4 antiferromagnet.In the case of H||c,a two-stage phase transition is observed.For H 上 c,a hump in the effective magnetic restoring force is noted,which implies the presence of spin reorientation as temperature increases.These results demonstrate the benefits of DCM for studying magnetism of 2D magnets.
查看更多>>摘要：We explore the structural evolutions of stoichiometric LiMO2 using the first-principles calculations combined with the cluster expansion method.We automatically obtain the ground state structures of the stoichiometric LiMO2 by just considering the cation orderings in the quasi rock-salt structures and the following structural relaxations due to both the atomic size mismatches and the Jahn-Teller distortions.We point out that,on the one hand,the cation orderings are mainly determined by the nearest,the second nearest,and the third nearest cation interactions and can be obtained from the'phase diagram'we have built using the relative strengths of effective cluster interaction(ECI).On the other hand,the structural relaxations are dominated by the crystal field splitting(CFS)energies,i.e.,structures with larger CFS energies are more stable.By calculating the ECIs and CFS energies for various structures of LiMO2,we clearly show how ECI and CFS play roles in determining the structural evolution mechanism of these systems.
查看更多>>摘要：Self-assembly of bacteria in electric fields is a promising route to fabricate biomaterials with reversible and specific structures.However,due to relatively less studies,our understanding of the self-assembly of bacteria in electric fields is still incomplete.Particularly,how different bacterial species behave differently in their field-mediated self-assembly behavior remains to bo disclosed.In this study,we choose four bacterial species,including Shewanella oneidensis,Pseudomonas aeruginosa,Bacillus subtilis and Lactococcus lactis as model systems,and investigate their self-assembly behavior in alternating-current(AC)electric fields for both diluted and concen-trated suspensions.The phase diagrams in the plane of applied field strength vs frequency are obtained.The results show that in diluted suspensions,a transition sequence of isotropic-paranematic-string-columnar phases is observed in all strains as the field strength increases.Details of the assembled structures are quantitatively differentiated among different strains.In concentrated suspensions,besides the isotropic and paranematic phases,a higher ordered phase with interdigitating rectangular crystal domains(OIR)and an ordered phase with smectic A liquid crystal domains are observed for S.oneidensis and P.aeruginosa,respectively.Our findings shed new light on fabricating potential biomaterials by assembling cells of appropriately chosen bacterial species that have desired surface properties under AC electric fields.
查看更多>>摘要：Fast radio bursts(FRBs)are short-duration radio transients with mysterious origins.Since their uncertainty,there are very few FRBs observed by different instruments simultaneously.This study presents a detailed analysis of a burst from FRB 20190520B observed by FAST and Parkes at the same time.The spectrum of this individual burst ended at the upper limit of the FAST frequency band and was simultaneously detected by the Parkes telescope in the 1.5-1.8 GHz range.By employing spectral energy distribution(SED)and spectral sharpness methods,we confirmed the presence of narrow-band radiation in FRB 20190520B,which is crucial for under-standing its radiation mechanisms.Our findings support the narrow-band characteristics that most repeaters exhibit.This work also highlights the necessity of continued multiband observations to explore its periodicity and frequency-dependent properties,contributing to an in-depth understanding of FRB phenomena.
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