查看更多>>摘要：A numerical study of the diamagnetic drift effect on the nonlinear interaction between multi-helicity neoclassical tearing modes(NTMs)is carried out using a set of four-field equations including two-fluid effects.The results show that,in contrast to the single-fluid case,5/3 NTM cannot be completely suppressed by 3/2 NTM with diamagnetic drift flow.Both modes exhibit oscillation and coexist in the saturated phase.To better understand the effect of the diamagnetic drift flow on multiple-helicity NTMs,the influence of typical relevant parameters is investigated.It is found that the average saturated magnetic island width increases with increasing bootstrap current fraction fb but decreases with the ion skin depth δ.In addition,as the ratio of parallel to perpendicular transport coefficients x||/x⊥ increases,the average saturated magnetic island widths of the 3/2 and 5/3 NTMs increase.The underlying mechanisms behind these observations are discussed in detail.
查看更多>>摘要：In the double-cone ignition schemes(DCIS),the deuterium-tritium target shell is ablated and compressed by a high-power nanosecond laser in Au-cones to generate plasmas.Under the actions of spherically symmetric compression and acceleration along the Au cone,they will be ejected out of the cone mouth and collide with each other.The plasmas experience conversion from kinetic energy to internal energy at the vertex of the geometric center of two Au cones that are symmetric to each other,because of which high-density fusion plasmas are preheated.This key physical process has undergone experimental verification on the Shenguang-Ⅱ upgraded facility in China.Apparently,the improvement and optimization of the velocity of plasmas in hypersonic jet flow at the cone mouth are crucial for the success of the DCIS.In the DCIR7 experiment of the Shenguang-Ⅱ upgraded facility,a velocity yield of approximately 130-260 km/s was achieved for the plasmas at the cone mouth,with a result of nearly 300 km/s based on numerical simulation.In this paper,theoretical analysis is performed as regards the process,in which target shells are ablated and compressed by laser to generate high-velocity plasmas ejected through jet flow.Based on this analysis,the formula for the velocity of plasmas in supersonic jet flow at the cone mouth is proposed.This study also provides measures that are more effective for improving the kinetic energy of plasmas and optimizing energy conversion efficiency,which can serve as theoretical references for the adjustment and optimization of processes in subsequent experiments.
查看更多>>摘要：Twisted bilayer graphene(TBG)has been extensively studied because of its novel physical properties and poten-tial application in electronic devices.Here we report the synthesis and characterization of 30° TBG naturally grown on Cu0.75Ni0.25(111)film and investigate the electronic structure by angle-resolved photoemission spectroscopy.Compared with other substrates,our TBG with a wafer scale is acquired with a shorter growth time.The Fermi velocity and energy gap of Dirac cones of TBG are comparable with those of a monolayer on Cu0.85Ni0.15(111).The signature of moiré lattices has not been observed in either the low-energy electron diffraction patterns or the Fermi surface map within experimental resolution,possibly due to different Cu and Ni contents in the substrates enhancing the different couplings between the substrate and the first/second layers and hindering the formation of a quasiperiodic structure.
查看更多>>摘要：Motivated by the recent discovery of unconventional superconductivity around a magnetic quantum critical point in pressurized CeSb2,here we present a high-pressure study of an isostructural antiferromagnetic(AFM)SmSb2 through electrical transport and synchrotron x-ray diffraction measurements.At PC～2.5 GPa,we found a pressure-induced mag-netic phase transition accompanied by a Cmca→ P4/nmm structural phase transition.In the pristine AFM phase below PC,the AFM transition temperature of SmSb2 is insensitive to pressure;in the emergent magnetic phase above PC,however,the magnetic critical temperature increases rapidly with increasing pressure.In addition,at ambient pressure,the magne-toresistivity(MR)of SmSb2 increases suddenly upon cooling below the AFM transition temperature and presents linear nonsaturating behavior under high field at 2 K.With increasing pressure above PC,the MR behavior remains similar to that observed at ambient pressure,both in terms of temperature-and field-dependent MR.This leads us to argue an AFM-like state for SmSb2 above PC.Within the investigated pressure of up to 45.3 GPa and the temperature of down to 1.8 K,we found no signature of superconductivity in SmSb2.
查看更多>>摘要：Saturation magnetization,magneto-crystalline anisotropy field,and dielectric properties are closely related to mi-crowave devices applied at different frequencies.For regulating the magnetic and dielectric properties of W-type bar-ium ferrites,single-phase BaMe2Fe16O27(Me=Fe,Mn,Zn,Ni,Co)with different Me ions were synthesized by the high-temperature solid-state method.The saturation magnetization(Ms)range from 47.77 emu/g to 95.34 emu/g and the magnetic anisotropy field(Ha)range from 10700.60 Oe(1 Oe=79.5775 A·m-1)to 13739.57 Oe,depending on the type of cation substitution in the hexagonal lattice.The dielectric permittivity and dielectric loss decrease with increasing frequency of the AC electric field in the low-frequency region,while they almost remain constant in the high-frequency region.The characteristics of easy regulation and preparation make it a potential candidate for use in microwave device applications.
查看更多>>摘要：In the phase diagram of the nickel-based superconductor Ba1-xSrvNi2As2,Tc has been found to be enhanced sixfold near the quantum critical point(QCP)x=0.71 compared with the parent compound.However,the mechanism is still under debate.Here,we report a detailed investigation of the superconducting properties near the QCP(x ≈ 0.7)by utilizing scanning tunneling microscopy and spectroscopy.The temperature-dependent superconducting gap and magnetic vortex state were obtained and analyzed in the framework of the Bardeen-Cooper-Schrieffer model.The ideal isotropic s-wave superconducting gap excludes the long-speculated nematic fluctuations while preferring strong electron-phonon coupling as the mechanism for Tc enhancement near the QCP.The lower than expected gap ratio of Δ/(kBTc)is rooted in the fact that Ba1-xSrxNi2As2 falls into the dirty limit with a serious pair breaking effect similar to the parent compound.
查看更多>>摘要：We synthesize high-quality single crystal of CeGaSi by a Ga self-flux method and investigate its physical properties through magnetic susceptibility,specific heat and electrical resistivity measurements as well as high pressure effect.Mag-netic measurements reveal that an antiferromagnetic order develops below Tm～10.4 K with magnetic moments orientated in the ab plane.The enhanced electronic specific heat coefficient and the negative logarithmic slope in the resistivity of CeGaSi indicate that the title compound belongs to the family of Kondo system with heavy fermion ground states.The max magnetic entropy change-ΔSmaxM(μ0H⊥c,μ0H=7 T)around Tm is found to reach up to 11.85 J·kg-1·K-1.Remark-ably,both the antiferromagnetic transition temperature and-ln T behavior increase monotonically with pressure applied to 20 kbar(1 bar=105 Pa),indicating that much higher pressure will be needed to reach its quantum critical point.
查看更多>>摘要：Quantum anomalous Hall(QAH)insulators have excellent properties driven by fancy topological physics,but their practical application is greatly hindered by the observed temperature of liquid nitrogen,and the QAH insulator with high Chem number is conducive to spintronic devices with lower energy consumption.Here,we find that monolayer FeSIn is a good candidate for realizing the QAH phase;it exhibits a high magnetic transition temperature of 221 K and tunable C=±2 with respect to magnetization orientation in the y-z plane.After the application of biaxial strain,the magnetic axis shifts from the x-y plane to the z direction,and the effect of the high C and ferromagnetic ground state on the stress is robust.Also,the effect of correlation U on C has been examined.These properties are rooted in the large size of the Fe atom that contributes to ferromagnetic kinetic exchange with neighboring Fe atoms.These findings demonstrate monolayer FeSIn to be a major template for probing novel QAH devices at higher temperatures.
查看更多>>摘要：Investigations on domain wall(DW)and spin wave(SW)modes in a series of nanostrips with different widths and thicknesses have been carried out using micromagnetic simulation.The simulation results show that the frequencies of SW modes and the corresponding DW modes are consistent with each other if they have the same node number along the width direction.This consistency is more pronounced in wide and thin nanostrips,favoring the DW motion driven by SWs.Further analysis of the moving behavior of a DW driven by SWs is also carried out.The average DW speed can reach a larger value of～140 m/s under two different SW sources.We argue that this study is very meaningful for the potential application of DW motion driven by SWs.
查看更多>>摘要：We perform 23Na nuclear magnetic resonance(NMR)and magnetization measurements on an S=1,quasi-2D honey-comb lattice antiferromagnet Na3Ni2BiO6.A large positive Curie-Weiss constant of 22.9 K is observed.The NMR spectra at low fields are consistent with a zigzag magnetic order,indicating a large easy-axis anisotropy.With the field applied along the c* axis,the NMR spectra confirm the existence of a 1/3-magnetization plateau phase between 5.1 T and 7.1 T.The transition from the zigzag order to the 1/3-magnetization plateau phase is also found to be a first-order type.A mono-tonic decrease of the spin gap is revealed in the 1/3-magnetization plateau phase,which reaches zero at a quantum critical field HC ≈ 8.35 T before entering the fully polarized phase.These data suggest the existence of exchange frustration in the system along with strong ferromagnetic interactions,hosting the possibility for Kitaev physics.Besides,well below the ordered phase,the 1/T1 at high fields shows either a level off or an enhancement upon cooling below 3 K,which suggests the existence of low-energy fluctuations.
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