Fluctuating specific heat in two-band superconductors

Theory of thermal fluctuations in two-band superconductors under an essentially homogeneous magnetic field is developed within the framework of the two-band Ginzburg-Landau theory. The fluctuating specific heat is calculated by using the optimized self-consistent perturbation approach and the results are applied to analyze the thermodynamic data of the iron-based superconductors Ba_(1-x)K_xFe_2As_2 with x ~0.4, which have been suggested to have a two-band structure by recent experiments. We estimate the fluctuation strength in this material and find that the specific heat is described well with the Ginzburg number Gi = 4 · 10~(-4). The influence of interband coupling strength is investigated and the result of the two-band Gaussian approximation approach is compared.     

Structural classification and a binary structure model for superconductors

Based on structural and bonding features, a new classification scheme of superconductors is proposed to classify them into three classes： three-dimensional, two-dimensional and molecule-assembled superconductors. The ＇sandwich model＇ for the high-Tc euprates is extended to a ＇binary structure model＇： i.e., the crystal structure of most super- conductors can be partitioned into two parts, a superconducting active component and a supplementary component. Partially metallic covalent bonding is found to be a common feature in all superconducting active components, and the electron states of the atoms in the active components usually make a dominant contribution to the energy band near the Fermi surface. Possible directions to explore new superconductors are discussed based on the structural classification and the binary structure model.     

Atom–field entanglement in the Jaynes Cummings model without rotating wave approximation

In this paper, we present a structure for obtaining the exact eigenfunctions and eigenvalues of the Jaynes–Cummings model(JCM) without the rotating wave approximation(RWA). We study the evolution of the system in the strong coupling region using the time evolution operator without RWA. The entanglement of the system without RWA is investigated using the Von Neumann entropy as an entanglement measure. It is interesting that in the weak coupling regime, the population of the atomic levels and Von Neumann entropy without RWA model shows a good agreement with the RWA whereas in strong coupling domain, the results of these two models are quite different.     

Visualizing the charge order and topological defects in an overdoped （Bi,Pb）2Sr2CuO6+x superconductor

Electronic charge order is a symmetry breaking state in high-Tc cuprate superconductors. In scanning tunneling microscopy, the detected charge-order-induced modulation is an electronic response of the charge order. For an overdoped(Bi,Pb)2Sr2CuO6+x sample, we apply scanning tunneling microscopy to explore local properties of the charge order. The ordering wavevector is nondispersive with energy, which can be confirmed and determined. By extracting its order-parameter field, we identify dislocations in the stripe structure of the electronic modulation, which correspond to topological defects with an integer winding number of ±1. Through differential conductance maps over a series of reduced energies, the development of different response of the charge order is observed and a spatial evolution of topological defects is detected. The intensity of charge-order-induced modulation increases with energy and reaches its maximum when approaching the pseudogap energy. In this evolution, the topological defects decrease in density and migrate in space. Furthermore, we observe appearance and disappearance of closely spaced pairs of defects as energy changes. Our experimental results could inspire further studies of the charge order in both high-Tccuprate superconductors and other charge density wave materials.     

Ultrafast Quasiparticle Dynamics and Electron-Phonon Coupling in (Li_(0.84)Fe_(0.16))OHFe_(0.98)Se

Distinctive superconducting behaviors between bulk and monolayer FeSe make it challenging to obtain a unified picture of all FeSe-based superconductors.We investigate the ultrafast quasiparticle(QP) dynamics of an intercalated superconductor(Li_(1-x)Fe_x)OHFe_(1-y)Se,which is a bulk crystal but shares a similar electronic structure with single-layer FeSe on SrTiO_3.We obtain the electron-phonon coupling(EPC) constant(0.22±0.04),which well bridges that of bulk FeSe crystal and single-layer FeSe on SrTiO_3.Significantly,we find that such a positive correlation between λ_(A_(1 g)) and superconducting T_c holds among all known FeSe-based superconductors,even in line with reported FeAs-based superconductors.Our observation indicates possible universal role of EPC in the superconductivity of all known categories of iron-based superconductors,which is a critical step towards achieving a unified superconducting mechanism for all iron-based superconductors.     

Energy Band and Josephson Dynamics of Spin-Orbit Coupled Bose–Einstein Condensates

We theoretically investigate the energy band structure and Josephson dynamics of a spin-orbit coupled Bose–Einstein condensate in a double-well potential. We study the energy band structure and the corresponding tunneling dynamics of the system by properly adjusting the SO coupling, Raman coupling, Zeeman field and atomic interactions.The coupled effects of SO coupling, Raman coupling, Zeeman field and atomic interactions lead to the appearance of complex energy band structure including the loop structure. Particularly, the emergence of the loop structure in energy band also depends on SO coupling, Raman coupling, Zeeman field and atomic interactions. Correspondingly,the Josephson dynamics of the system are strongly related to the energy band structure. Especially, the emergence of the loop structure results in complex tunneling dynamics, including suppression-revival transitions and self-trapping of atoms transfer between two spin states and two wells. This engineering provides a possible means for studying energy level and corresponding dynamics of two-species SO coupled BECs.     

Some Topological Properties of Anyons

In this paper, starting with the well known U（1） Chern-Simons Lagrangian and the covariant derivative of a complex scalar matter field, we give a detailed discussion of some topological properties of anyons. We show that the ＂basic＂ charge carried by anyons has an inner structure and can be decomposed in terms of the Chern-Simons coupling and the gauge coupling constants of the theory. Also some incorrect results obtained in the literature are revised.     

Novel 0–π transitions in Josephson junctions between noncentrosymmetric superconductors

We study the Josephson effect between two noncentrosymmetric superconductors(NCSs) with opposite polarization vectors of Rashba spin–orbit coupling(RSOC).We find a 0–π transition driven by the triplet–singlet ratio of NCSs.Different from conventional 0–π transitions,the Andreev bound states change their energy range instead of phase shift in the 0–π transition found here.This novel property results in a feature that the critical current becomes almost zero at the transition point,not only a minimum.Furthermore,when the directions of RSOC polarization vectors are the same in two NCSs,the similar effect can also be found in the presence of a perpendicular exchange field or a Dresselhause spin–orbit coupling in the interlayer.We find novel oscillations of critical current without 0–π transition.These novel 0–π transitions or oscillations of critical current present new understanding of the Josephson effect and can also serve as a tool to determine the unknown triplet–singlet ratio of NCSs.     

Modal Characterization of a Planar Waveguide in Bismuth Borate Crystal

We report on the fabrication and modal property studies of planar waveguide structure in x-cut bismuth borate biaxial crystal formed by He ion implantation with triple energies. The prism coupling method is used to measure the effective refractive indices of this waveguide. We reconstruct the refractive index distribution of this waveguide by the reflectivity calculation method. Our results indicate that a broadened optical barrier is produced by the multiple He ion implantations. The so-called tunneling effect of the non-stationary mode in this type of barrier waveguide is presented by the well-known finite difference beam propagation method.     

Extension of Linear Response Regime in Weak-Value Amplification Technique

The achievable precision of parameter estimation plays a significant role in evaluating a strategy of metrology.In practice,one may employ approximations in a theoretical model development for simplicity,which,however,will cause systematic error and lead to a loss of precision.We derive the error of maximum likelihood estimation in the weak-value amplification technique where the linear approximation of the coupling parameter is used.We show that this error is positively related to the coupling ...