Mechanisms of the pancake vortex and vortex line movement in the high Tc superconductors Bi2Sr2CaCu2O8 δand La1.93Sr0.07CuO4 δ

In the strict sense, it is not very clear why with magnetic field increasing, the normal-superconductive (NS) transition becomes broad for Bi2Sr2CaCu2O8 δ(Bi2212) while the NS transitions are almost parallel for La1.93Sr0.07CuO4 δ(La214). In this paper, R-T relations are measured by the six-probe method. We propose a moving mechanism of the pancake vortex and vortex line for Bi2212. The theoretical curves fit the experiment data well.     

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.     

Temperature Evolution of Energy Gap and Band Structure in the Superconducting and Pseudogap States of Bi_2Sr_2CaCu_2O_(8+δ) Superconductor Revealed by Laser-Based Angle-Resolved Photoemission Spectroscopy

We carry out detailed momentum-dependent and temperature-dependent measurements on Bi_2Sr_2CaCu_2O_(8+δ)(Bi2212) superconductor in the superconducting and pseudogap states by super-high resolution laser-based angleresolved photoemission spectroscopy. The precise determination of the superconducting gap for the nearly optimally doped Bi2212(T_c= 91 K) at low temperature indicates that the momentum-dependence of the superconducting gap deviates from the standard d-wave form(cos(2Φ)). It can be alternatively fitted by including a high-order term(cos(6Φ)) in which the next nearest-neighbor interaction is considered. We find that the band structure near the antinodal region smoothly evolves across the pseudogap temperature without a signature of band reorganization which is distinct from that found in Bi_2Sr_2CuO_(6+δ) superconductors. This indicates that the band reorganization across the pseudogap temperature is not a universal behavior in cuprate superconductors.These results provide new insights in understanding the nature of the superconducting gap and pseudogap in high-temperature cuprate superconductors.     

Evolution of incommensurate superstructure and electronic structure with Pb substitution in(Bi_(2-x)Pb_x)Sr_2CaCu_2O_(8+δ) superconductors

High-quality Bi_(2-x)Pb_xSr_2 CaCu_2O_(8+δ)(Bi2212) single crystals have been successfully grown by the traveling solvent floating zone technique with a wide range of Pb substitution(x = 0–0.8).The samples are characterized by transmission electron microscope(TEM) and measured by high resolution laser-based angle-resolved photoemission spectroscopy(ARPES) with different photon energies.A systematic evolution of the electronic structure and superstructure with Pb substitution has been revealed for the first time.The superstructure shows a significant change with Pb substitution and the incommensurate modulation vector(Q) decreases with increasing Pb substitution.In the meantime, the superstructure intensity from ARPES measurements also decreases dramatically with increasing Pb concentration.The superstructure in Bi2212 can be effectively suppressed by Pb substitution and it nearly disappears with a Pb substitution of x = 0.8.We also find that the superstructure bands in ARPES measurements depend sensitively on the photon energy of lasers used;they can become even stronger than the main band when using a laser photon energy of 10.897 eV.These results provide important information on the origin of the incommensurate superstructure and its control and suppression in bismuth-based high temperature superconductors.     

Continuously Doping Bi2Sr2CaCu2O8+δ into Electron-Doped Superconductor by CaH2 Annealing Method

As a typical hole-doped cuprate superconductor, Bi₂Sr₂CaCu₂O_8+δ(Bi2212) carrier doping is mostly determined by its oxygen content. Traditional doping methods can regulate its doping level within the range of hole doping.Here we report the first application of CaH₂ annealing method in regulating the doping level of Bi2212. By continuously controlling the anneal time, a series of differently doped samples can be obtained. The combined experime...     

Microwave Response of Bi2Sr2CaCu2O8+δ Surface Intrinsic Josephson Junctions with Bending Pancake Vortices

We study the microwave response of surface intrinsic Josephson junctions on Bi2Sr2 CaCu2O8＋δ, in which bending pancake vortex lines are introduced in a controllable way. It is found that the bending vortices can greatly influence the response. In some cases, typical Shapiro steps that lie far above the quasiparticle branch are observed, with the step interval satisfying the Josephson relation and their amplitude versus the square root of microwave power following the Bessel function behaviour. In the other cases, current steps that lie on the quasiparticle branch are observed, but only one or two steps appear at the same time under the variation of the microwave power.     

Magneto-resistance and vortex phase diagram of BaNi_（0.1）Fe_（1.9）As_2 single crystal

The transition from vortex glass to a liquid phase is studied in Ba Ni0.1Fe1.9As2 single crystal with Tc = 19.4 K by magneto-resistance measurements. The resistivity curves are measured in magnetic fields in a range of 0 T–13 T for H‖c and H⊥c. Good scalings for all values of resistivity ρ（H, T） and the effective pinning potential U0（H, T） are obtained with the modified vortex glass theory by using the critical exponents s and H0. Phase diagrams for H‖c and H⊥c are determined based on the obtained vortex glass temperature Tg, the vortex dimensionality crossover temperature T＊, and the upper critical magnetic field Hc2. Our results suggest that both below and above 5 T, single vortex pinning co-exists with collective creep, and collective creep is dominant. There is a narrower vortex liquid region for H⊥c than for H‖c in the vortex phase diagram, which may originate from a stronger pinning force.     

Possible Nodeless Superconducting Gaps in Bi_2Sr_2CaCu_2O_(8+δ) and YBa_2Cu_3O_(7-x) Revealed by Cross-Sectional Scanning Tunneling Spectroscopy

Pairing in the cuprate high-temperature superconductors and its origin remain among the most enduring mysteries in condensed matter physics.With cross-sectional scanning tunneling microscopy/spectroscopy we clearly reveal the spatial-dependence or inhomogeneity of the superconducting gap structure of Bi_2Sr_2CaCu_2O_(8+δ)(Bi2212) and YBa_2Cu_3O_(7-x)(YBCO) along their c-axes on a scale shorter than the interlayer spacing.By tunneling into the(100) plane of a Bi2212 single crystal and a YBCO film,we observe both U-shaped tunneling spectra with extended flat zero-conductance bottoms,and V-shaped gap structures,in different regions of each sample.On the YBCO film,tunneling into a(110) surface only reveals a U-shaped gap without any zero-bias peak.Our analysis suggests that the U-shaped gap is likely a nodeless superconducting gap.The V-shaped gap has a very small amplitude,and is likely proximity-induced by regions having the larger U-shaped gap.     

Molecule opacities of X~2Σ~+, A~2Π, and B~2Σ~+ states of CS~+

Carbon sulfide cation(CS~+) plays a dominant role in some astrophysical atmosphere environments. In this work, the rovibrational transition lines are computed for the lowest three electronic states, in which the internally contracted multireference configuration interaction approach(MRCI) with Davison size-extensivity correction(+Q) is employed to calculate the potential curves and dipole moments, and then the vibrational energies and spectroscopic constants are extracted. The Frank–Condon factors are calculated for the bands of X~2~+Σ~+–A~2Π and X~2Σ~+–B~2Σ~+systems, and the band of X~2Σ~+–A~2Π is in good agreement with the available experimental results. Transition dipole moments and the radiative lifetimes of the low-lying three states are evaluated. The opacities of the CS~+ molecule are computed at different temperatures under the pressure of 100 atms. It is found that as temperature increases, the band systems associated with different transitions for the three states become dim because of the increased population on the vibrational states and excited electronic states at high temperature.     

Subsolidus phase relation in the Bi_2O_3–Fe_2O_3–La_2O_3 system

Bismuth-containing semiconductor material is a hot topic in photocatalysts because of its effective absorption under the visible light.In this paper,we expect to explore a new bismuth-based photocatalyst by studying the subsolidus phase relations of the Bi2O3–Fe2O3–La2O3system.The X-ray diffraction data shows that in this ternary system the ternary compound does not exist,while seven binary compounds(including one solid solution series Bi1 xLaxO1.5with 0.167≤x≤0.339)are obtained and eight compatibility triangles are determined.     

Dynamics of vortex–antivortex pair in a superconducting thin strip with narrow slits

In the framework of phenomenological time-dependent Ginzburg-Landau(TDGL) formalism,the dynamical properties of vortex-antivortex(V-Av) pair in a superconductor film with a narrow slit was studied.The slit position and length can have a great impact not only on the vortex dynamical behavior but also the current-voltage(Ⅰ-Ⅴ) characteristics of the sample.Kinematic vortex lines can be predominated by the location of the slit.In the range of relatively low applied currents for a constant weak magnetic field,kinematic vortex line appears at right or left side of the slit by turns periodically.We found such single-side kinematic vortex line cannot lead to a jump in the Ⅰ-Ⅴ curve.At higher applied currents the phase-slip lines can be observed at left and right sides of the slit simultaneously.The competition between the vortex created at the lateral edge of the sample and the V-Av pair in the slit will result in three distinctly different scenarios of vortex dynamics depending on slit length:the lateral vortex penetrates the sample to annihilate the antivortex in the slit;the V-Av pair in the slit are driven off and expelled laterally;both the lateral vortex and the slit antivortex are depinned and driven together to annihilation in the halfway.     

Integrability and Solutions of the(2+1)-dimensional Hunter–Saxton Equation

In this paper,the(2+1)-dimensional Hunter-Saxton equation is proposed and studied.It is shown that the(2+1)-dimensional Hunter–Saxton equation can be transformed to the Calogero–Bogoyavlenskii–Schiff equation by reciprocal transformations.Based on the Lax-pair of the Calogero–Bogoyavlenskii–Schiff equation,a non-isospectral Lax-pair of the(2+1)-dimensional Hunter–Saxton equation is derived.In addition,exact singular solutions with a finite number of corners are obtained.Furthermore,the(2+1)-dimensional μ-Hunter–Saxton equation is presented,and its exact peaked traveling wave solutions are derived.     

The Topological Structure of the SU（2） Chern-Simons Topological Current in the Four-Dimensional Quantum Hall Effect

In the light of the decomposition of the SU（2） gauge potential for I = 1/2, we obtain the SU（2） Chern-Simons current over S4, i.e. the vortex current in the effective field for the four-dimensional quantum Hall effect. Similar to the vortex excitations in the two-dimensional quantum Hall effect （2D FQH） which are generated from the zero points of the complex scalar field, in the 4D FQH, we show that the SU（2） Chern-Simons vortices are generated from the zero points of the two-component wave functions ψ, and their topological charges are quantized in terms of the Hopf indices and Brouwer degrees of Ф-mapping under the condition that the zero points of field ψ are regular points.     

Study on superstructure in ion co-doped BiFeO3 by using transmission electron microscopy

La3+and V5+co-doped Bi Fe O3 ceramics are synthesized by rapid liquid sintering technique. The modulated structure in Bi0.85La0.15Fe0.97V0.03O3 is investigated by using transmission electron microscopy(TEM). Two kinds of superstructures are observed in the samples. One is the component modulated superstructure and twin-domain, which is generated by La3+ordered substitution for Bi3+and frequently appears. The chemical composition of the superstructure is explored by x-ray energy dispersive spectroscopy(EDS). The model of the ordered structure is proposed. Simulation based on the model is conducted. The second is the fluorite-type δ-Bi2O3 related superstructure. The relation between the ferroelectric property and the microstructure of the sample is also discussed.     

Nonlocal symmetry and exact solutions of the(2+1)-dimensional modified Bogoyavlenskii–Schiff equation

In this paper,the truncated Painlev′e analysis,nonlocal symmetry,Bcklund transformation of the(2+1)-dimensional modified Bogoyavlenskii–Schiff equation are presented.Then the nonlocal symmetry is localized to the corresponding nonlocal group by the prolonged system.In addition,the(2+1)-dimensional modified Bogoyavlenskii–Schiff is proved consistent Riccati expansion(CRE) solvable.As a result,the soliton–cnoidal wave interaction solutions of the equation are explicitly given,which are difficult to find by other traditional methods.Moreover figures are given out to show the properties of the explicit analytic interaction solutions.     

Positon and hybrid solutions for the(2+1)-dimensional complex modified Korteweg–de Vries equations

Solving nonlinear partial differential equations have attracted intensive attention in the past few decades. In this paper, the Darboux transformation method is used to derive several positon and hybrid solutions for the(2+1)-dimensional complex modified Korteweg–de Vries equations. Based on the zero seed solution, the positon solution and the hybrid solutions of positon and soliton are constructed. The composition of positons is studied, showing that multi-positons of(2+1)-dimensional equations...     

Near-infrared lateral photovoltaic effect of epitaxial LaTiO--_(3+δ) films under high pressure

A lateral photovoltaic effect(LPE) is discovered in an La TiO_(3+δ)film epitaxially grown on a(100) Sr TiO_3 substrate. Under the illumination of a continuous 808 nm laser beam that is focused on the La TiO_(3+δ)film through the Sr TO3 substrate, the open-circuit photovoltage depends linearly on the illuminated position. The sensitivity of the LPE can be modified by the bias current. The La TiO_(3+δ)film shows a stable photoelectric property under the high pressure, up to 9 MPa. These results indicate that the La TiO_(3+δ)films can give rise to a potentially photoelectronic device for near-infrared position-sensitive detection in high-pressure environments.     

Influences of Thalliation on the Morphology and Critical Temperature of Tl2Ba2CaCu2O8 Thin Films

Tl2Ba2CaCu2Ox(Tl-2212) thin films were prepared by the two-step technique.A precursor film was first prepared by the pulsed laser deposition method,and then experienced the incorporation of thalliation in a one-step or two-step annealing process.The experimental results show that the two-step annealing process produces dense and smooth films,and that the one-step annealing process produces a high critical temperature film of 101K,but the transition width is wide.Precursor films with homogeneous Ba2Ca1.3Cu2.1Ox composition are essential for producing high-quality Tl-2212 films.     

Tunable superconductivity in parent cuprate Pr_2CuO_(4±δ) thin films

We studied the role of oxygen in Pr2 CuO_(4±δ) thin films fabricated by the polymer assisted deposition method. The magnetoresistance and Hall resistivity of Pr2 CuO_(4±δ) samples were systematically investigated. It was found that with decreasing oxygen content, the low-temperature Hall coefficient(RH) and magnetoresistance changed from negative to positive, similar to those with the increase of Ce-doped concentration in R_(2-x)Ce_x CuO_4 (R = La, Nd, Pr, Sm, Eu). In addition, we observed that the dependence of the superconducting critical temperature Tc with RH for the Pr_(2-x) Ce_x CuO_4 perfectly overlapped with that of Pr_2 CuO_(4±δ) . These findings point to the fact that the doped electrons induced by the oxygen removal are responsible for the superconductivity of the T-phase parent compounds.     

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...