Pressure-Tuned Intrinsic Anomalous Hall Conductivity in Kagome Magnets RV_(6)Sn_(6)(R=Gd,Tb)

Exploration of exotic phenomena in magnetic topological systems is at the frontier of condensed matter physics,holding a significant promise for applications in topological spintronics.However,complex magnetic structures carrying nontrivial topological properties hinder its progresses.Here,we investigate the pressure effect on the novel topological kagome magnets GdV_(6)Sn_(6) and TbV_(6)Sn_(6) to dig out the interplay between magnetic Gd/Tb layers and nonmagnetic V-based kagome sublattice.The pressure-tuned magnetic transition temperature Tm in both the compounds exhibit a turning point at the critical pressure P_(c),accompanied with a sign reversal in anomalous Hall effect(AHE).The separation of intrinsic and extrinsic contributions using the Tian-Ye-Jin scaling model suggests that the intrinsic mechanism originating from the electronic Berry curvature holds the priority in the competition with extrinsic mechanism in AHE.The above-mentioned findings can be attributed to the combined effect of pressure-tuned band topology and magnetic interaction in segregated layers.Our results provide a practical route to design and manipulate the intrinsic AHE in magnetic topological materials.

Manipulating charge density wave state in kagome compound RbV_(3)Sb_(5)

Owing to the unique electronic structure,kagome materials AV_(3)Sb_(5)(A=K,Rb,Cs)provide a fertile platform of quantum phenomena such as the strongly correlated state and topological Dirac band.It is well known that RbV_(3)Sb_(5)exhibits a 2×2 unconventional charge density wave(CDW)state at low temperature,and the mechanism is controversial.Here,by using scanning tunneling microscopy/spectroscopy(STM/STS),we successfully manipulated the CDW state in the Sb plane of RbV_(3)Sb_(5),and realized a new3(1/2)×3(1/2)modulation together with the ubiquitous 2×2 period in the CDW state of RbV_(3)Sb_(5).This work provides a new understanding of the collective quantum ground states in the kagome materials.

Comparison Studies on Dynamic Packaging Properties of Corrugated Paperboard Pads

Corrugated paperboard is a kind of inexpensive and environmental-friendly packaging material, and may be made into pads of package cushioning to protect products from shock and vibration damage by isolation during distribution. This article deals with the characterization of dynamic packaging properties of corru-gated paperboard pads, such as dynamic cushioning curves, vibration transmissibility and frequency curves. The main feature of article is the evaluation on the dynamic shock cushioning property and vibration trans-missibility of corrugated paperboard pads by a series of experimental studies on the drop shock tester and vibration tester, the establishment of experimental formulas of dynamic cushioning curves, and the analysis of resonance frequencies and vibration transmissibility. By using the fitting polynomial of curve and method of the least mean square, the experimental formulas with third order polynomial function of dynamic cush-ioning curves for corrugated paperboard pads are obtained. By using linear vibration theory with single de-gree of freedom, the resonance frequencies, vibration transmissibility and damping ratios of corrugated pa-perboard pads at different static loads are acquired. All results show the dynamic properties relevant to de-sign applications of corrugated paperboard pads for protective packaging.

Determination of the surface states from the ultrafast electronic states in a thermoelectric material

We reveal the electronic structure in Yb Cd_(2)Sb_(2),a thermoelectric material,by angle-resolved photoemission spectroscopy(ARPES)and time-resolved ARPES(tr ARPES).Specifically,three bulk bands at the vicinity of the Fermi level are evidenced near the Brillouin zone center,consistent with the density functional theory(DFT)calculation.It is interesting that the spin-unpolarized bulk bands respond unexpectedly to right-and left-handed circularly polarized probe.In addition,a hole band of surface states,which is not sensitive to the polarization of the probe beam and is not expected from the DFT calculation,is identified.We find that the non-equilibrium quasiparticle recovery rate is much smaller in the surface states than that of the bulk states.Our results demonstrate that the surface states can be distinguished from the bulk ones from a view of time scale in the nonequilibrium physics.

High-pressure study of topological semimetals XCd_(2)Sb_(2)(X=Eu and Yb)

Topological materials have aroused great interest in recent years,especially when magnetism is involved.Pressure can effectively tune the topological states and possibly induce superconductivity.Here we report the high-pressure study of topological semimetals XCd_(2)Sb_(2)(X=Eu and Yb),which have the same crystal structure.In antiferromagnetic(AFM)Weyl semimetal EuCd_(2)Sb_(2),the Néel temperature(TN)increases from 7.4 K at ambient pressure to 50.9 K at 14.9 GPa.When pressure is above 14.9 GPa,the AFM peak of resistance disappears,indicating a non-magnetic state.In paramagnetic Dirac semimetal candidate YbCd_(2)Sb_(2),pressure-induced superconductivity appears at 1.94 GPa,then Tc reaches to a maximum of 1.67 K at 5.22 GPa and drops to zero at about 30 GPa,displaying a dome-shaped temperature–pressure phase diagram.High-pressure x-ray diffraction measurement demonstrates that a crystalline-to-amorphous phase transition occurs at about 16 GPa in YbCd_(2)Sb_(2),revealing the robustness of pressure-induced superconductivity against structural instability.Similar structural phase transition may also occur in EuCd_(2)Sb_(2),causing the disappearance of magnetism.Our results show that XCd_(2)Sb_(2)(X=Eu and Yb)is a novel platform for exploring the interplay among magnetism,topology,and superconductivity.

Observation of large in-plane anisotropic transport in van der Waals semiconductor Nb_(2)SiTe_(4)

Two-dimensional(2D)van der Waals material is a focus of research for its widespread application in optoelectronics,memories,and spintronics.The ternary compound Nb_(2)SiTe_(4) is a van der Waals semiconductor with excellent air stability and small cleavage energy,which is suitable for preparing a few layers counterpart to explore novel properties.Here,properties of bulk Nb_(2)SiTe_(4) with large in-plane electrical anisotropy are demonstrated.It is found that hole carriers dominate at a temperature above 45 K with a carrier active energy of 31.3 meV.The carrier mobility measured at 100 K is about 213 cm^(2)·V^(-1)·s^(-1) in bulk Nb_(2)SiTe_(4),higher than the reported results.In a thin flake Nb_(2)SiTe_(4),the resistivity ratio between the crystalline axes of a and b is reaching about 47.3 at 2.5 K,indicating that there exists a large anisotropic transport behavior in their basal plane.These novel transport properties provide accurate information for modulating or utilizing Nb_(2)SiTe_(4) for electronic device applications.

Measurement of electronic structure in van der Waals ferromagnet Fe_(5-x)GeTe_(2)

As a van der Waals ferromagnet with high Curie temperature,Fe_(5-x)GeTe_(2) has attracted tremendous interests recently.Here,using high-resolution angle-resolved photoemission spectroscopy(ARPES),we systematically investigated the electronic structure of Fe_(5-x)GeTe_(2) crystals and its temperature evolution.Our ARPES measurement reveals two types of band structures from two different terminations with slight kz evolution.Interestingly,across the ferromagnetic transition,we observed the merging of two split bands above the Curie temperature,suggesting the band splitting due to the exchange interaction within the itinerant Stoner model.Our results provide important insights into the electronic and magnetic properties of Fe_(5-x)GeTe_(2) and the understanding of magnetism in a two-dimensional ferromagnetic system.

Photoemission Spectroscopic Evidence of Multiple Dirac Cones in Superconducting BaSn_(3)

Signatures of topological superconductivity(TSC)in superconducting materials with topological nontrivial states prompt intensive researches recently.Utilizing high-resolution angle-resolved photoemission spectroscopy and first-principles calculations,we demonstrate multiple Dirac fermions and surface states in superconductor BaSn_(3) with a critical transition temperature of about 4.4 K.We predict and then unveil the existence of two pairs of type-Ⅰtopological Dirac fermions residing on the rotational axis.Type-ⅡDirac fermions protected by screw axis are confirmed in the same compound.Further calculation for the spin helical texture of the observed surface states originating from the Dirac fermions gives an opportunity for realization of TSC in one single material.Hosting multiple Dirac fermions and topological surface states,the intrinsic superconductor BaSn_(3) is expected to be a new platform for further investigation of topological quantum materials as well as TSC.

Pullback Random Attractors for Non-Autonomous Stochastic Fractional FitzHugh-Nagumo System

This paper is concerned with the asymptotic behavior of solutions for a class of non-autonomous fractional FitzHugh-Nagumo equations deriven by additive white noise. We first provide some sufficient conditions for the existence and uniqueness of solutions, and then prove the existence and uniqueness of tempered pullback random attractors for the random dynamical system generated by the solutions of considered equations in an appropriate Hilbert space. The proof is based on the uniform estimates and the decomposition of dynamical system.

Absence of metallicity and bias-dependent resistivity in low-carrier-density EuCd_(2)As_(2)

EuCd_(2)As_(2)was theoretically predicted to be a minimal model of Weyl semimetals with a single pair of Weyl points in the ferromagnet state.However,the heavily p-doped Eu Cd_(2)As_(2)crystals in previous experiments prevent direct identification of the semimetal hypothesis.Here,we present a comprehensive magneto-transport study of high-quality Eu Cd_(2)As_(2)crystals with ultralow bulk carrier density(10^(13)cm^(-3)).In contrast to the general expectation of a Weyl semimetal phase,Eu Cd_(2)As_(2)shows insulating behavior in both antiferromagnetic and ferromagnetic states as well as surface-dominated conduction from band bending.Moreover,the application of a dc bias current can dramatically modulate the resistance by over one order of magnitude,and induce a periodic resistance oscillation due to the geometric resonance.Such nonlinear transport results from the high nonequilibrium state induced by an electrical field near the band edge.Our results suggest an insulating phase in Eu Cd_(2)As_(2)and put a strong constraint on the underlying mechanism of anomalous transport properties in this system.

Experimental observation of multiple topological nodal structure in LaSb_(2)

Unconventional fermions in the immensely studied topological semimetals are the source for rich exotic topological properties.Here,using symmetry analysis and first-principles calculations,we propose the coexistence of multiple topological nodal structure in LaSb_(2),including topological nodal surfaces,nodal lines and in particular eightfold degenerate nodal points,which have been scarcely observed in a single material.Further,utilizing angle-resolved photoemission spectroscopy,we confirm the existence of nodal surfaces and eightfold degenerate nodal points in LaSb_(2).The intriguing multiple topological nodal structure might play a crucial role in giving rise to the large linear magnetoresistance.Our work renews the insights into the exotic topological phenomena in LaSb_(2).

Kagome晶格补偿型半金属Ni_(3)In_(2)S_(2)创纪录的高迁移率和极大磁电阻现象

具有Kagome晶格的晶体有很多有趣的性质,包括受挫磁阻、电荷有序、拓扑态、超导和关联现象.为了在电子学和自旋电子学应用中实现高性能Kagome晶格化合物,需要对能带结构仔细调整.本文采用输运测量、角分辨光电子能谱和从头计算等方法研究了Kagome晶格晶体Ni_(3)In_(2)S_(2)的电子结构.输运测量表明,Ni_(3)In_(2)S_(2)是一种在Kagome晶格材料中具有创纪录的高载流子迁移率(空穴和电子迁移率分别约为8683和7356 cm^(2)V^(-1)S^(-1))和极大磁电阻(在2 K和13 T时为15,518%)的补偿半金属.Ni在Kagome晶格中的3d电子导致的非直接带隙、小的电子/空穴口袋和大的带宽的能带结构特征很好地解释了这些特殊的性质.这项工作表明,晶体场和掺杂是优化Kagome晶格晶体输运特性的关键因素.我们的工作为Kagome晶格半金属在电子学和自旋电子学方面的应用提供了材料基础和优化路径.

反铁磁拓扑绝缘体MnBi_(2)Te_(4)/Bi_(2)Te_(3)超晶格具有不变近零能隙的表面态研究

磁性拓扑材料蕴含拓扑磁电效应等丰富拓扑物理现象,成为近年来拓扑量子材料研究热点.最近,在本征反铁磁拓扑绝缘体MnBi_(2)Te_(4)中发现了量子反常霍尔效应及轴子绝缘体态,使得此体系引发了广泛的关注.由MnBi_(2)Te_(4)及Bi_(2)Te_(3)插层得到的超晶格结构材料(MnBi_(2)Te_(4))m(Bi_(2)Te_(3))n,同样具有本征反磁序及非平庸拓扑相,为研究磁性与拓扑电子结构相互关系提供了重要的可调控材料平台.本文利用具有空间分辨能力的激光和同步辐射角分辨光电子能谱系统(ARPES),全面且系统地测量了此材料体系中Mn Bi4Te7的电子结构,发现在MnBi2Te4及Bi2Te3解理面均存在近零能隙的拓扑表面态;文章通过变温测量,发现其体态电子受到反铁磁序的强烈影响,但其拓扑表面态在反铁磁相变时保持近零能隙不变.这些结果印证了MnBi2Te4体系的不变近零能隙的普遍性,为理解中磁性与拓扑物态之间相互作用以及其调控提供了重要的谱学信息.

Cu2Se相变过程中热电效率增强的电子起源

热电材料可实现热能向电能的转换,是解决能源危机的潜在方式.目前热电材料的发展受限于较低的热电转换效率(可由热电优值zT评估),探索新型高zT热电材料或提升现有热电材料的z T值是亟待解决的重要课题.Cu2Se作为一种传统的超离子高z T热电材料一直备受关注.研究表明在其400 K附近的相变过程中,z T迅速提升了3倍.目前对这一变化的研究多限于晶体结构方面,而电子性质研究仅限于理论计算.本文利用高分辨角分辨光电子能谱技术,详细测量了相变过程其能带结构随温度的演变,揭示了相变过程中Cu2Se的电子结构的剧烈重组.作者利用光电子强度近似的模拟Cu2Se费米能级附近的电子态随温度的演化,并采用Mott模型来估算在相变过程中Seebeck系数的演化,再现了输运实验中Seebeck系数的提升.本研究表明电子结构在体系的热电性质中起了非常重要的作用,为理解和优化材料的热电性能提供了一种可能的方法.

Lump solutions and interaction solutions for(2+1)-dimensional KPI equation

The lump solutions and interaction solutions are mainly investigated for the(2+1)-dimensional KPI equation.According to relations of the undetermined parameters of the test functions,the N-soliton solutions are showed by computations of the Maple using the Hirota bilinear form for(2+1)-dimensional KPI equation.One type of the lump solutions for(2+1)-dimensional KPI equation has been deduced by the limit method of the N-soliton solutions.In addition,the interaction solutions between the lump and N-soliton solutions of it are studied by the undetermined interaction functions.The sufficient conditions for the existence of the interaction solutions are obtained.Furthermore,the new breather solutions for the(2+1)-dimensional KPI equation are considered by the homoclinic test method via new test functions including more parameters than common test functions.

Ferroelectricity in hBN intercalated double-layer graphene

Van der Waals(vdW)assembly of two-dimensional materials has long been recognized as a powerful tool for creating unique systems with properties that cannot be found in natural compounds[Nature 499,419(2013)].However,among the variety of vdW heterostructures and their various properties,only a few have revealed metallic and ferroelectric behaviour signatures[Sci.Adv.5,eaax5080(2019);Nature 560,336(2018)].Here we show ferroelectric semimetal made of double-gated double-layer graphene separated by an atomically thin crystal of hexagonal boron nitride.The structure demonstrates high room temperature mobility of the order of 10 m2·V^(−1)·s^(−1) and exhibits ambipolar switching in response to the external electric field.The observed hysteresis is reversible and persists above room temperature.Our fabrication method expands the family of ferroelectric vdW compounds and offers a promising route for developing novel phase-changing devices.A possible microscopic model of ferroelectricity is discussed.