High-temperature pairing in stripes

That the superconducting transition in underdoped high temperature superconductors is controlled by phase ordering, implies that pairing is a local phenomenon that occurs on an intermediate length scale, and typically at a temperature aboveT _c . The discovery of local stripe order in the LSCO family of high temperature superconductors, along with the theoretical suggestion that such structures are a general feature of doped antiferromagnets lead us further to propose that in fact pairing occurs in the vicinity of an individual stripe. The transition to a superconducting state then follows at lower temperature due to Josephson coupling between stripes. In this paper we review our microscopic model of high temperature pairing on individual stripes.     

Electron-electron and electron-hole pairing in graphene structures

The superconducting pairing of electrons in doped graphene owing to in-plane and out-of-plane phonons is considered. It is shown that the structure of the order parameter in the valley space substantially affects conditions of the pairing. Electron-hole pairing in a graphene bilayer in the strong coupling regime is also considered. Taking into account retardation of the screened Coulomb pairing potential shows a significant competition between the electron-hole direct attraction and their repulsion owing to virtual plasmons and single-particle excitations.     

Physical pictures of the pairing interaction in the Hubbard model

Physical pictures which have been suggested to describe the pairing interaction in a two-dimensional Hubbard model doped near half-filling are compared with numerical Monte Carlo results. We find that the single spin-fluctuation exchange picture provides a reasonable representation if Monte Carlo results are used for the spin susceptibility. We also find that the spatial structure of the pairing interaction in the singlet channel is repulsive when both fermions are on the same site but attractive when they are on near-neighbor sites favouring $d_{x^2 - y^2 } $ pairing correlations.     

Condensate theory versus pairing theory for degenerate Bose systems

The statistical variational principle for the thermodynamic potential is used to investigate the quantum statistically degenerate phase of an interacting Bose system. Starting with a general mean-field trial Hamiltonian, we find a set of integral equations that has two different types of solution: (a) the condensate sssssstheory with a finite c-number part for the lowest momentum state operator; (b) the pairing theory with zero c-number part. The condensate theory is identical to the self-consistent Hartree-Fock-Bogoliubov approximation of the Beliaev equations, whereas the pairing theory is identical to the theory proposed by Evans and Imry. We solve the resulting integral equations for both theories numerically and show that—independent of the special form of interacting potentials—the condensate theory gives the lower free energy and the higher transition temperature. Therefore we conclude that the condensate theory describes the thermodynamically stable state rather than the pairing theory.Project of the Sonderforschungsbereich Frankfurt/Darmstadt financed by special funds of the Deutsche Forschungsgemeinschaft.     

Effects of disorder on the electron pairing

The electron pairing in randomly disordered lattices is studied by using an attractive Hubbard model, and by mapping the many-body problem onto a tight-binding one in a higher dimensional space, where a diagonal disorder is considered within the coherent-potential approximation. The results show an enhancement of the pair-binding energy as the self-energy difference increases in a binary alloy A_xB_1–x. This fact suggests that the pairing process is highly sensitive to the one-particle localization condition. A ground-state phase diagram for on-site interaction disorder shows regions where pairing is avoid for ordered diatomic systems but not for disordered case.     

Optimal pairing computation over families of pairing-friendly elliptic curves

Vercauteren introduced the concept of optimal pairing, which by definition can be computed by using at most (log₂ r)/φ(k) + log₂ k basic Miller iterations, where r is the order of the groups involved and k is the embedding degree Vercauteren (IEEE Trans Inf Theory 56(1):455–461, 2010). Freeman et al. summarized and proposed all of the new constructions of pairing-friendly elliptic curves that currently exist Freeman et al. (J Cryptol 23(2):224–280, 2010). In this paper, we give an optimal pairing for each family of pairing-friendly curves in Freeman et al. (J Cryptol 23(2):224–280, 2010) by taking the Ate or R-ate pairing approach.     

协作分集OFDM系统的混合排序子载波配对算法

考虑到信源子载波和中继子载波的配对能在频率选择信道环境下提高协作分集系统的性能,对协作分集正交频分复用(OFDM)系统的子载波配对进行了研究,推导了2种特殊情况下的最佳子载波配对方法,即顺序配对和逆序配对,在此基础上,提出了一种基于混合排序的子载波配对算法.该算法根据信源-中继链路、信源-目标链路和中继-目标链路上的每个子载波的信噪比状态,自适应地选择顺序配对或逆序配对.仿真结果表明,提出的混合排序子载波配对算法能显著提高系统的平均可取得速率,性能明显优于顺序配对和逆序配对.     

Tracing magnetism and pairing in FeTe-based systems

Magnetism in the Fe-chalcogenide FeTe, under various modulations, provides important clues with regard to possible precursors to superconductivity. In this study, we monitor the non-superconducting chalcogenide FeTe and follow its transitions under insertion of oxygen, Fe, doping with Se, and vacancies of Fe using spin-polarized band structure methods (utilizing GGA) originating from the collinear and bicollinear magnetic arrangements. We use a supercell of Fe₈Te₈ as our starting point, so that it can capture local changes in magnetic moments. For the most part, the calculated values of magnetic moments agree well with available experimental data prior to superconducting transitions with some of the modulations leading to significant changes in the bicollinear or collinear magnetic moments/arrangements. The total energies of these systems indicate that the collinear-derived structure is the more favorable one prior to a possible superconducting transition. Using the Hubbard model on a 8-site Betts-cluster-based lattice, we show why these systems favor electron or hole pairing under appropriate modulations and could lead to a common understanding of charge and spin pairing in the cuprates, pnictides, and chalcogenides.     

BoxStep methods for crew pairing problems

Crew pairing problems are often solved using column generation in a branch-and-price framework. The oscillation of dual points is the main reason which leads to instability in the standard implementation of this method. One device to deal with the problem is to use the trust-region idea to stabilize the path of dual points. Therefore, a so-called stabilized column generation with respect to control parameters is suggested to overcome this problem. In this paper we report about possible realizations of this principle and show that the performance of algorithms can be improved significantly. Three stabilizing methods are used to investigate good control parameters which contribute to the improved computation time in solving a set of crew pairing problems involving about 400 flights per week.     

Energy scale of the pairing model with energy-dependent density of state

The critical temperature of a pairing model for HT _c S has been calculated using an energy-dependent density of states. We showed that the problem which is connected with the van Hove scenario is very sensitive to the energy scale and to the behavior of the density of states at low and high energy.     

Coherent pairing of excitons in insulators and semiconductors

A microscopic theory is developed concerning the coherent pairing of Wannier-Mott type excitons in insulators and semiconductors. The coherent pairing of excitons occurs in the presence of a resonant electromagnetic field and the resulting energy gap is in competition with that induced by the electromagnetic field. Due to the electrical neutrality of the electron-hole pairs, the excitation spectrum is of the excitonic insulator type and the presence of the electromagnetic field results in the splitting of the energies of excitation. The expression for the coherent gap function depends on the exciton density, the effective exciton mass, the exciton-exciton interaction, and the effective energy band gap, which is equal to the difference between the transition frequency and the frequency of the field and the binding energy of the exciton. Under resonance conditions and at temperatures below some valueT _c , the biexciton state can exist provided that the dielectric gap is less than that for the biexciton state. The ground-state energy resulting from the coherent pairing of excitons is calculated and is found to be lower in energy than the normal exciton state. This indicates the existence of a bound biexciton state as long as there is a net attractive exciton-exciton interaction.Issued as NRCC No. 15395.     

An exact study of pairing fluctuations and phase diagrams in four-site Hubbard Nanoclusters

Charge-spin separation and pairing fluctuations and pseudogaps are studied using the analytical eigenvalues of the four-site Hubbard Nanoclusters with the grand canonical and canonical ensemble approaches in a multidimensional parameter space of temperature (T), magnetic field (h), on-site interaction (U), chemical potential (μ), and number of electrons (N). The electron charge energy gap, with one hole off half filling, corresponds to an excitonic particle–hole pair binding energy Δ ^e-h > 0 at U > U _c and vanishes at a critical parameter U _c = 4.584. For U < U _c, particle–particle pair binding is found with a pairing energy Δ^p > 0. In addition, for U ⩽ U _c we find an electron pair binding instability at finite temperature near N ≈ 3, which manifests a possible pairing mechanism, a precursor to superconductivity, in small clusters. The resulting phase diagram, consisting of charge and spin pseudogaps, hole pairing near 1/8th filling with hole-rich and hole-poor regions in the ensemble of Nanoclusters, closely resembles the phase diagrams in the family of doped high-T _c-cuprates.     

Solvation structure,hydrogen bonding,and ion pairing in dilute supercritical aqueous NaCl mixtures

We review molecular dynamics simulations of infinitely dilute supercritical aqueous NaCl solutions to determine the solvation structure and the soluteinduced effect on water water hydrogen bonding and report new simulation results On the extent of the ion pairing. Our simulation studies indicate that Na⁺ and Cl ions as a pair or its isolated infinitely dilute ions form strong solvation structures in SCW. even though the water eater hydrogen bonding is not affected Within the context of the models we are using. there is strong indication of a high degree of Na⁺ CI ion pairing.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994. Boulder, Colorado. U.S.A.     

上行虚拟MIMO系统的双比例公平用户配对算法

在分析上行虚拟多输入多输出(V-MIMO)系统的传统正交用户配对算法的基础上,提出了一种先按比例公平准则选取第一个用户,然后基于一种改进的比例公平准则选取其配对用户的新的双比例公平(D-PF)用户配对算法,并基于不同的接收机结构分析评估了该算法的吞吐量性能以及用户之间的公平度.仿真结果表明,与传统的正交用户配对算法相比,所提D-PF算法能够取得更好的吞吐量和用户公平度性能.     

Current states and domains in systems with electron-hole pairing

Nonlinear collective excitations and inhomogeneous states of the excitonic phase are examined with the interband transitions of pairing particles taken into account. We obtain a Ginzburg-Landau-like equation and find the necessary conditions for a second-order phase transition to take place. The nonlinear equation describing the excited (inhomogeneous) state of the system in a simple case appears to be the Sine-Gordon equation. It is shown that domains of magnetization or polarization appear in the excited state of the excitonic antiferromagnetic or antiferroelectric. There are also other excited states, where the charge density coexists with the magnetization density. The collective excitations are manifested as nonlinear magnetization or polarization waves, moving domains of magnetization, etc.     

Constraints on the pairing state of the cuprate superconductors

The pairing state of the cuprate superconductors is a key issue in understanding experiments and in clarifying possible mechanisms. A wide range of experiments now show that the gap function is predominantly in character. Here we discuss the relevant experiments, especially focusing on those which provide constraints on possible mixed pairing states, such as s+d and s+id.     

The influence off-wave pairing fluctuations on sound propagation in superfluid3He-A

The theory of sound propagation in pair-correlated Fermi liquids developed previously by Wölfle, with additionalf-wave pairing fluctuations, is applied to the ABM state. Expressions for the anisotropic sound absorption and velocity at arbitrary temperature and frequency in the collisionless limit are derived. Thef-wave pairing fluctuations give a large effect on the normal-flapping mode frequency at low temperatures. The corresponding shift in the sound attenuation peak of this collective mode provides a sensitive probe of thef-wave pair coupling constantg ₃. There is also a pronounced effect on the super-flapping mode attenuation peak, which becomes well defined whenf-wave pairing fluctuations are considered.     

Exact solution to the pairing equations for bosons in a one-dimensional model

Pairing equations for bosons interacting with a delta-function potential in one dimension are reduced to two coupled equations involving complete elliptic integrals. These equations are solved numerically and the results are compared to the exact Lieb and Liniger solution for the problem of one-dimensional bosons with delta-function interactions. One finds that the pairing solution gives too large a potential energy and too small a kinetic energy. We also compare the exact and paired excitation spectra. We discuss the relevance of these results to realistic problems.Work supported in part by the National Science Foundation.     

汽车继电器用AgMeO触点材料不同配对方式时的性能

为了探究触点配对方式对汽车继电器电接触性能的影响,选取AgMeO型触头材料进行实验,采用粉末冶金法制备AgSnO₂, AgCuO和AgZnO 3种触头材料,并测量其物理性能,采用JF04C电接触触点材料测试系统,按5种不同触点配对方式进行电接触实验,并对实验前后的阴阳极触点进行称量,实验结果表明：触点配对方式对接触电阻,材料转移和损耗影响较大,对燃弧能量的影响较小,通过对触点进行不对称配对可以明显降低接触电阻和材料转移和损耗,明显改善汽车继电器的接触性能.     

Electronic Raman scattering as a probe of anisotropic electron pairing

A theory for the electronic contribution to Raman scattering in anisotropic superconductors is presented. It is shown that Raman scattering can provide a wealth of polarization-(symmetry-) dependent information which probes the detailed angular dependence of the energy gap. Using a model band structure, the symmetry-dependent Raman spectra are calculated for d_x2-_y2 pairing and compared to the data taken on Bi₂Sr₂CaCu₂O₈. Favorable agreement with the symmetry-dependent electronic spectra is shown. Further, the impurity dependence of theory is calculated, which provides an unique test of d_x2-_y2 pairing.