Electronic Evolution from the Parent Mott Insulator to a Superconductor in Lightly Hole-Doped Bi2Sr2CaCu2O8+σ

High temperature superconductivity in cuprates is realized by doping the Mott insulator with charge carriers. A central issue is how such an insulating state can evolve into a conducting or superconducting state when charge carriers are introduced. Here, by in situ vacuum annealing and Rb deposition on the Bi₂Sr₂Ca_0.6Dy_0.4Cu₂O_8+σ(Bi2212) sample surface to push its doping level continuously from deeply underdoped(T_c = 25...     

Tuning of Magnetic Properties of α-RuCl3 Single Crystal by Cr Doping

We study the influence of Cr doping on magnetic properties of α-RuCl₃ single crystals in detail.With increasing Cr content,the c-axial lattice parameter increases gradually,implying that the Cr doping may weaken the interlayer interactions.The magnetism of Ru_1-xCr_xCl₃ single crystals evolves from a long-range AFM order to a possible spin-glass state with Cr doping.The appearance of a possible spin-glass state can be explained by the introduction of FM ...     

Enhanced photogalvanic effect in the two-dimensional MgCl2/ZnBr2 vertical heterojunction by inhomogenous tensile stress

The photogalvanic effect (PGE) occurring in noncentrosymmetric materials enables the generation of a dc photocurrent at zero bias with a high polarization sensitivity, which makes it very attractive in photodetection. However, the magnitude of the PGE photocurrent is usually small, leading to a low photoresponsivity, and therefore hampers its practical application in photodetection. Here, we propose an approach to largely enhancing the PGE photocurrent by applying an inhomogenous mechanical stretch, based on quantum transport simulations. We model a two-dimensional photodetector consisting of the wide-bandgap MgCl₂/ZnBr₂ vertical van der Waals heterojunction with the noncentrosymmetric C_3v symmetry. Polarization-sensitive PGE photocurrent is generated under the vertical illumination of linearly polarized light. By applying inhomogenous mechanical stretch on the lattice, the photocurrent can be largely increased by up to 3 orders of magnitude due to the significantly increased device asymmetry. Our results propose an effective way to enhance the PGE by inhomogenous mechanical strain, showing the potential of the MgCl₂/ZnBr₂ vertical heterojunction in the low-power UV photodetection.     

Growth and Characterization of a New Superconductor GaBa2Ca3Cu4O11+δ

We successfully grow a new superconductor GaBa₂Ca₃Cu₄O_11+δ(Ga-1234) with a transition temperature of 113 K, using the Walker-type high-pressure synthesis apparatus. X-ray diffraction measurements on the powderized samples show a mixture of the Ga-1234 phase and the Ca_0.85CuO₂ phase, and the former is dominant. Under the scanning electron microscope, plate-like crystals of the Ga-based 1234 phase with shiny surfaces can be seen.The...     

A Reproducible Approach of Preparing High-Quality Overdoped Bi_2Sr_2CaCu_2O_(8+δ) Single Crystals by Oxygen Annealing and Quenching Method

We report a reproducible approach in preparing high-quality overdoped Bi_2Sr_2CaCu_2O_(8+δ)(Bi2212) single crystals by annealing Bi2212 crystals in high oxygen pressure followed by a fast quenching.In this way,high-quality overdoped and heavily overdoped Bi2212 single crystals are obtained by controlling the annealing oxygen pressure.We find that,beyond a limit of oxygen pressure that can achieve most heavily overdoped Bi2212 with a T_c ~63K,the annealed Bi2212 begins to decompose.This accounts for the existence of the hole-doping limit and thus the T_c limit in the heavily overdoped region of Bi2212 by the oxygen annealing process.These results provide a reliable way in preparing high-quality overdoped and heavily overdoped Bi2212 crystals that are important for studies of the physical properties,electronic structure and superconductivity mechanism of the cuprate superconductors.     

Prediction of Superhard BN2 with High Energy Density

Considering that pressure-induced formation of short,strong covalent bonds in light-element compounds can produce superhard materials,we employ structure searching and first-principles calculations to predict a new class of boron nitrides with a stoichiometry of BN₂,which are stable relative to alpha-B and alpha-N₂ at ambient pressure.At ambient pressure,the most stable phase has a layered structure(h-BN₂) containing hexagonal BN layers between which there are intercalated N₂ molecules.At 25 GPa,a three-dimensional P4₂/mmc structure with single N-N bonds becomes the most stable.Dynamical,thermal,and mechanical stability calculations reveal that this structure can be recovered under ambient conditions.Its calculated stress-strain relations demonstrate an intrinsic superhard nature with an estimated Vickers hardness of ~43 GPa.This structure has a potentially high energy density of ~4.19 kJ/g.     

CVD法单层MoS2在209Bi离子辐照下的损伤效应研究

通过光学显微镜、拉曼光谱确定了CVD（化学气相沉积法）制备的不同厚度MoS₂的层数,采用拉曼分析结合原子力显微镜观测分析了由HIRFL提供的高能209Bi离子辐照CVD制备的单层MoS₂样品随辐照注量的损伤规律。随辐照注量增加,E_2g1和A_1g两种声子振动模式对应的拉曼峰逐渐蓝移,且拉曼特征峰强度减弱,这是由于带正电荷的209Bi辐照产生潜径迹型晶格缺陷吸附空气中氧分子而引入p型掺杂引起的。同时,在辐照注量为5×1010 ions/cm2的单层MoS₂的AFM图像中观察到潜径迹主要以凹坑形式出现,与机械剥离法观测到的凸起径迹明显不同,分析了不同制备工艺对径迹形貌的影响。比较了机械剥离法制备MoS₂样品的拉曼光谱和AFM成像的实验数据和结果,认为不同制备方法会影响单层或少层MoS₂的电子密度。The layer number of MoS₂ with different thickness was determined by the optical microscope and Raman spectra. And the damage effect of the CVD (chemical vapor deposition) prepared single-layer MoS₂ sample irradiated by 209Bi ions was analyzed by the combination of Raman analysis and AFM observations. With the increase of irradiation fluence, the Raman characteristic peaks of E_2g1 and A_1g corresponding to both phonon vibration modes gradually bluely shift, and the intensity of the peaks obviously decreased. This is due to the fact that the 209Bi ion irradiation results in the latent track type lattice defects and they adsorb the oxygen molecules in the air ended with the p-type doping. Meanwhile, from the AFM image of the mono-layer of irradiated MoS₂ under the 5×1010 ions/cm2, it can been seen that latent tracks mainly occur in the form of pits, which different from the hillock tracks observed by mechanical stripping method. The influence of different preparation technology to the track morphology is analyzed. Compared with the Raman and AFM results of MoS₂ prepared by mechanical stripping, it is considered that different preparation methods will affect the electron density in single or few layers of MoS₂.     

Flat Band and Z2 Topology of Kagome Metal CsTi3Bi5

The simple kagome-lattice band structure possesses Dirac cones, flat band, and saddle point with van Hove singularities in the electronic density of states, facilitating the emergence of various electronic orders. Here we report a titanium-based kagome metal CsTi₃Bi₅ where titanium atoms form a kagome network, resembling its isostructural compound CsV₃Sb₅. Thermodynamic properties including the magnetization, resistance, and heat capacity reveal the co...     

THE STRUCTURE AND MAGNETIC PROPERTIES OF La2-2xSr1Ca2xMn2O7 (x=0.25－1.00)

In this paper, the effect of divalent cation substitution on the structure and magnetic properties in La_2-2xSr₁Ca_2xMn₂O₇ have been investigated systematically using bulk samples with a wide doping concentration range 0.25≤x≤1.00. Replacing trivalent La ions by divalent Ca ions results in the weakening and then disappearance of the long-range ferromagnetic (FM) ordering, the formation of spin canting, antiferromagnetic (AFM) ordering and low-temperature spin-glass. These results show that increasing the hole-doping concentration significantly suppresses the FM state. We suggest that this variation of magnetic properties is related to the competition of the FM and AFM interactions resulting from the change of Mn³⁺/Mn⁴⁺ ratio and Jahn-Teller-type lattice distortion of MnO₆ octahedra due to the introduction of Ca²⁺ ions.     

Zcs(4000)+ and Zcs(4220)+ in a Multiquark Color Flux-Tube Model

We systematically investigate the mass spectrum, spatial configuration and magnetic moment of the ground and p-wave states ■ with various color-spin configurations in a multiquark color flux-tube model. Numerical results indicate that the state Z_cs(4000)⁺ can be described as the compact state ■ with 1³S₁. Its main colorspin configuration is ■ and its magnetic moment is 0.73μN. The state Z_cs(4220)⁺can be depicted as the compact sta...     

Electronic structures and optical properties of Zn-doped β-Ga2O3 with different doping sites

<正>The electronic structures and optical properties of intrinsicβ-Ga₂O₃ and Zn-dopedβ-Ga₂O₃ are investigated by first-principles calculations.The analysis about the thermal stability shows that Zn-dopedβ-Ga₂O₃ remains stable. The Zn doping does not change the basic electronic structure ofβ-Ga₂O₃,but only generates an empty energy level above the maximum of the valence band,which is shallow enough to make the Zn-dopedβ-Ga₂O₃ a typical p-type semiconductor.Because of Zn doping,absorption and reflectivity are enhanced in the near infrared region.The higher absorption and reflectivity of Zn_Ca（2） than those of Zn_Ca（1）are due to more empty energy states of Zn_Ca（2）than those of Zn_Ca（1） near E_f in the near infrared region.     

Theoretical investigation of CoTa206/graphene heterojunctions for oxygen evolution reaction

Water electrolysis is to split water into hydrogen and oxygen using electricity as the driving force.To obtain low-cost hydrogen in a large scale,it is critical to develop electrocatalysts based on earth abundant elements with a high efficiency.This computational work started with Cobalt on CoTh₂C)₆surface as the active site,CoTa₂O₆/Graphene heterojunctions have been explored as potential oxygen evolution reaction(OER)catalysts through density functional theory(DFT).We demonstrated that the electron transfer(₆)from CoTa₂C)₆to graphene substrate can be utilized to boost the reactivity of Co-site,leading to an OER overpotential as low as 0.30 V when N-doped graphene is employed.Our findings offer novel design of heterojunctions as high performance OER catalysts.     

Femtosecond Fiber Laser Based on BiSbTeSe2 Quaternary Material Saturable Absorber

Topological insulator materials, including Bi₂Te₃, Sb₂Te₃, Sb₂Te₃, and Bi₂Se₃, have attracted some attention due to their narrow band gaps, high carrier mobility, wide spectral absorption ranges and other characteristics.We report a new multi-compound topological insulator material BiSbTeSe₂ that, compared with the traditional topological insulator composed of two elements, can integrate the physic...     

不同氧含量Bi2Sr2CaCu2O８+δ单晶电阻率的各向异性

精确测量了在不同氧压下退火的单晶Bi₂Sr₂CaCu₂O_8+δ(Bi2212)样品的Cu-O面内和Cu-O面外的电阻率ρ_c(T)和ρ_ab(T).发现ρ_c(T)和各向异性比(ρ_c(T)/ρ_ab(T))随着载流子浓度增加而迅速下降.在过掺杂样品中,高于120K时,ρ_c随温度线性下降,而各向异性 关键词：     

Neutron Spectroscopy Evidence for a Possible Magnetic-Field-Induced Gapless Quantum-Spin-Liquid Phase in a Kitaev Material α-RuCl3

As one of the most promising Kitaev quantum-spin-liquid（QSL） candidates,α-RuCl₃ has received a great deal of attention.However,its ground state exhibits a long-range zigzag magnetic order,which defies the QSL phase.Nevertheless,the magnetic order is fragile and can be completely suppressed by applying an external magnetic field.Here,we explore the evolution of magnetic excitations of α-RuCl₃ under an in-plane magnetic field,by carrying out inelastic neutron scattering measu...     

First-principles study on with nitrogen and anatase TiO2 codoped praseodymium

<正>The crystal structures,electronic structures and optical properties of nitrogen or/and praseodymium doped anatase TiO₂ were calculated by first principles with the plane-wave ultrasoft pseudopotential method based on density functional theory.Highly efficient visible-light-induced nitrogen or/and praseodymium doped anatase TiO₂ nanocrystal photocatalyst were synthesized by a microwave chemical method.The calculated results show that the photocatalytic activity of TiO₂ can be enhanced by N doping or Pr doping,and can be further enhanced by N+Pr codoping.The band gap change of the codoping TiO₂ is more obvious than that of the single ion doping,which results in the red shift of the optical absorption edges.The results are of great significance for the understanding and further development of visible-light response high activity modified TiO₂ photocatalyst.The photocatalytic activity of the samples for methyl blue degradation was investigated under the irradiation of fluorescent light.The experimental results show that the codoping TiO₂ photocatalytic activity is obviously higher than that of the single ion doping.The experimental results accord with the calculated results.     

Fermi surface gapping in the hidden order state of PrFe4P12;by point-contact spectroscopy

We have applied point-contact spectroscopy(PCS) to investigate the nonmagnetic hidden order(HO) state of the skutterudite compound PrFe₄P₁₂ with its transition temperature THO~6.5 K. Its point-contact conductance curves exhibit a reproducible gap structure in the HO state below THOand its temperature dependent gap magnitude follows a BCS-like mean-field behavior.A Fano-like conductance shape is observed to emerge below the coherence temperature of PrFe₄P₁₂. In a magnetic field, the gap feature is gradually suppressed and evolves into a pronounced Fano peak, signaling the heavy fermion state and vividly demonstrating the competition between HO and the formation of heavy fermion states. Our results strongly suggest the itinerant characteristic of f electrons in PrFe₄P₁₂, which constrains theoretical models to explain the HO mechanism.     

PHASE TRANSITIONS IN Bi2Sr2(Cu1-zFez)O6+δ

We have investigated, by X-ray diffraction, a series of single crystals of Bi-based oxides with the nominal composition Bi₂Sr₂(Cu_1-zFe_z)O_6+δ(0≤z≤0.55). In this system we observed two structural phase transitions with the increase of the doping content. The first transition, from an incommensurate monoclinic phase to an incommensurate orthorhombic phase, occurs at a doping content of iron z_Fe=0.027. The second one corresponds to a phase transition from an incommensurate orthorhombic phase to a commensurate orthorhombic phase at z_Fe=0.34. The comparison of these results with those for more limited substitutions of Zn and Ni indicates the significant role of the insertion of the extra oxygen in the (Bi-O)_∞ double layers.     

Single crystal growth and characterizations of iron arsenide superconductor BaFe2-xNixAs2（0.0≤x≤0.12）

A series of big single crystals of BaFeFe_2-xNi_xAs₂ have been prepared by the FeAs self-flux method, with nominal nickel doping x = 0--0.12. The dimensions of the cleaved crystals are over 10~mm along ab plane and ～ 2~mm in maximum along the c direction. The measurements of x-ray diffraction, electrical resistance and magnetic property are carried out on the crystals. For the undoped parent compound BaFe₂As₂, both resistance and magnetization data display an anomaly associated with spin density wave and/or structural phase transition, with the transition temperatures at ～ 138~K. For Ni-doped BaFe_2-xNi_xAs₂ crystals, the superconducting critical temperature T_c ranges from 4.3~K for x=0.06 sample to 20~K for the optimally doped x=0.10 crystal.     

Effects of dipolar interactions on the magnetic hyperthermia of Zn0.3Fe2.7O4 nanoparticles with different sizes

Tumor-targeted magnetic hyperthermia has recently attracted much attention.Magnetic nanoparticles(NPs) are heat mediator nanoprobes in magnetic hyperthermia for cancer treatment.In this paper,single cubic spinel structural Zn_0.3Fe_2.7O₄ magnetic NPs with sizes of 14 nm-20 nm were synthesized,followed by coating with SiO₂ shell.The SLP value of Zn_0.3Fe_2.7O₄/SiO₂ NPs below 20 nm changes non-monotonically with the concentration of solution under the alternating current(AC) magnetic field of 430 kHz and 27 kA/m.SLP values of all Zn_0.3Fe_2.7O₄/SiO₂ NPs appear a peak value with change of solution concentration.The solution concentrations with optimal SLP value decrease with increasing magnetic core size.This work can give guidance to the better prediction and control of the magnetic hyperthermia performance of materials in clinical applications.