Spin waves in the block checkerboard antiferromagnetic phase

Motivated by the discovery of new family 122 iron-based superconductors, we present the theoretical results on the ground state phase diagram, spin wave and dynamic structure factor of the extended $J_{1}-J_{2}$ Heisenberg model. In the reasonable physical parameter region of $K_{2}Fe_{4}Se_{5}$, we fi{}nd the block checkerboard antiferromagnetic order phase is stable. There are two acoustic branches and six optical branches spin wave in the block checkerboard antiferromagnetic phase, which has analytic expression in the high symmetry points. To compare the further neutron scattering experiments, we discuss the saddlepoint structure in the magnetic excitation spectrum and calculate the predicted inelastic neutron scattering pattern based on linear spin wave theory

Superconductivity induced by oxygen deficiency in Sr-doped LaOFeAs

We synthesized Sr-doped $La_{0.85}Sr_{0.15}OFeAs$ sample with single phase, and systematically studied the effect of oxygen deficiency in the Sr-doped LaOFeAs system. It is found that substitution of Sr for La indeed induces the hole carrier evidenced by positive thermoelectric power (TEP), but no bulk superconductivity is observed. The superconductivity can be realized by annealing the as-grown sample in vacuum to produce the oxygen deficiency. With increasing the oxygen deficiency, the superconducting transition temperature ($T_c$) increases and maximum $T_c$ reaches about 26 K the same as that in La(O,F)FeAs. TEP dramatically changes from positive to negative in the nonsuperconducting as-grown sample to the superconducting samples with oxygen deficiency. While $R_H$ is always negative for all samples (even for Sr-doped as grown sample). It suggests that the $La_{0.85}Sr_{0.15}O_{1-\delta}FeAs$ is still electron-type superconductor.Comment: 4 pages, 4 figure

Transport properties and superconductivity in Ba1−xMxFe2As2Ba_{1-x}M_xFe_2As_2 (M=La and K) with double FeAs layers

We synthesized the samples $Ba_{1-x}M_xFe_2As_2$ (M=La and K) with $ThCr_2Si_2$-type structure. These samples were systematically characterized by resistivity, thermoelectic power (TEP) and Hall coefficient ($R_H$). $BaFe_2As_2$ shows an anomaly in resistivity at about 140 K. Substitution of La for Ba leads to a shift of the anomaly to low temperature, but no superconducting transition is observed. Potassium doping leads to suppression of the anomaly in resistivity and induces superconductivity at 38 K as reported by Rotter et al.\cite{rotter}. The Hall coefficient and TEP measurements indicate that the TEP is negative for $BaFe_2As_2$ and La-doped $BaFe_2As_2$, indicating n-type carrier; while potassium doping leads to change of the sign in $R_H$ and TEP. It definitely indicates p-type carrier in superconducting $Ba_{1-x}K_xFe_2As_2$ with double FeAs layers, being in contrast to the case of $LnO_{1-x}F_xFeAs$ with single FeAs layer. A similar superconductivity is also observed in the sample with nominal composition $Ba_{1-x}K_xOFe_2As_2$.Comment: 4 pages, 4 figure

Exact Analysis of Scaling and Dominant Attractors Beyond the Exponential Potential

By considering the potential parameter $\Gamma$ as a function of another potential parameter $\lambda$[47], We successfully extend the analysis of two-dimensional autonomous dynamical system of quintessence scalar field model to the analysis of three-dimension, which makes us be able to research the critical points of a large number of potentials beyond the exponential potential exactly. We find that there are ten critical points in all, three points $P_{3, 5, 6}$} are general points which are possessed by all quintessence models regardless of the form of potentials and the rest points are closely connected to the concrete potentials. It is quite surprising that, apart from the exponential potential, there are a large number of potentials which can give the scaling solution when the function $f(\lambda)(=\Gamma(\lambda)-1)$ equals zero for one or some values of $\lambda_{*}$ and if the parameter $\lambda_{*}$ also satisfies the condition Eq.(16) or Eq.(17) at the same time. We give the differential equations to derive these potentials $V(\phi)$ from $f(\lambda)$. We also find that, if some conditions are satisfied, the de-Sitter-like dominant point $P_4$ and the scaling solution point $P_9$(or $P_{10}$) can be stable simultaneously but $P_9$ and $P_{10}$ can not be stable simultaneity. Although we survey scaling solutions beyond the exponential potential for ordinary quintessence models in standard general relativity, this method can be applied to other extensively scaling solution models studied in literature[46] including coupled quintessence, (coupled-)phantom scalar field, k-essence and even beyond the general relativity case $H^2 \propto\rho_T^n$. we also discuss the disadvantage of our approach.Comment: 16 pages,no figure, this new revision has taken the suggestions from CQG referees and has been accepted for publication in Classical and Quantum Gravit

Angular dependence of resistivity in the superconducting state of NdFeAsO0.82_{0.82}F0.18_{0.18} single crystals

We report the results of angle dependent resistivity of NdFeAsO$_{0.82}$F$_{0.18}$ single crystals in the superconducting state. By doing the scaling of resistivity within the frame of the anisotropic Ginzburg-Landau theory, it is found that the angle dependent resistivity measured under different magnetic fields at a certain temperature can be collapsed onto one curve. As a scaling parameter, the anisotropy $\Gamma$ can be determined for different temperatures. It is found that $\Gamma(T)$ increases slowly with decreasing temperature, varying from $\Gamma \simeq$ 5.48 at T=50 K to $\Gamma \simeq$ 6.24 at T=44 K. This temperature dependence can be understood within the picture of multi-band superconductivity.Comment: 7 pages, 4 figure

Coexistence of superconductivity and antiferromagnetism in single crystals A0.8Fe2−ySe2A_{0.8}Fe_{2-y}Se_2 (A= K, Rb, Cs, Tl/K and Tl/Rb): evidence from magnetization and resistivity

We measure the resistivity and magnetic susceptibility in the temperature range from 5 K to 600 K for the single crystals $A$Fe$_{2-y}$Se$_2$ ($A$ = K$_{0.8}$, Rb$_{0.8}$, Cs$_{0.8}$, Tl$_{0.5}$K$_{0.3}$ and Tl$_{0.4}$Rb$_{0.4}$). A sharp superconducting transition is observed in low temperature resistivity and susceptibility, and susceptibility shows 100% Meissner volume fraction for all crystals, while an antiferromagnetic transition is observed in susceptibility at Neel temperature ($T_N$) as high as 500 K to 540 K depending on A. It indicates the coexistence of superconductivity and antiferromagnetism. A sharp increase in resistivity arises from the structural transition due to Fe vacancy ordering at the temperature slightly higher than $T_{\rm N}$. Occurrence of superconductivity in an antiferromagnetic ordered state with so high $T_{\rm N}$ may suggest new physics in this type of unconventional superconductors.Comment: 5 pages, 4 figure