Hole dispersions for antiferromagnetic spin-\hbox{$\frac{1}{2}$}12 two-leg ladders by self-similar continuous unitary transformations

The hole-doped antiferromagnetic spin-\hbox{ \frac12\frac{1}{2}}12 two-leg ladder is an important model system for the high-T _c superconductors based on cuprates. Using the technique of self-similar continuous unitary transformations we derive effective Hamiltonians for the charge motion in these ladders. The key advantage of this technique is that it provides effective models explicitly in the thermodynamic limit. A real space restriction of the generator of the transformation allows us to explore the experimentally relevant parameter space. From the effective Hamiltonians we calculate the dispersions for single holes. Further calculations will enable the calculation of the interaction of two holes so that a handle of Cooper pair formation is within reach.     

Structural studies of La \mathsf{_{1-x}}Sr\mathsf{_{x}}MnO \mathsf {_{3 + \delta}} (x = 0.1-1.0)

We report here for the first time (particularly for $x \ge 0.5$ ) a systematic structural study using Rietveld Profile Refinement of powder X-ray diffraction data on the series of polycrystalline compounds La_1-x Sr _x MnO $_{3 + \delta}$ (0.1 ≤ x ≤ 1.0). The iodometric redox titration results show that the compounds $0.1\le x\le 0.4$ and the end compound are oxygen excess and deficient respectively and the compounds in the compositional range 0.5 ≤ x ≤ 0.9 are oxygen stoichiometric within the experimental error. It is found that the structure remains hexagonal until x = 0.4 composition. On further doping, at x = 0.5 composition, a structural transition to orthorhombic phase is observed. Around this composition, very small variations in the Mn-O(2)-Mn and average Mn-Mn bond distances are observed. For above x = 0.5, until x = 0.8 composition, the structure remains orthorhombic with reduced orthorhombic distortion. For the next compound, x = 0.9, a mixed hexagonal and orthorhombic phase is observed where the hexagonal phase is 6 layered with stacking sequence of ABCACB type and the orthorhombic phase is more distorted than that of x = 0.8 composition. The end compound is a four layered hexagonal structure with stacking sequence ABAC type which is more distorted than ABCACB type. As one goes down the series, a decrease in the volume per formula unit and average Mn-O bond distance are observed except at x = 0.9 composition. The observed structural transitions from hexagonal to orthorhombic to layered hexagonal phase can be explained under the electrostatic limit.     

Topological Basis Method for Four-Qubit Spin-$\frac {1}{2}$ XXZ Heisenberg Chain with Dzyaloshinskii-Moriya Interaction

In this paper, we investigate the four-qubit spin-\(\frac {1}{2}\) XXZ Heisenberg chain with Dzyaloshinskii-Moriya interaction by topological basis method, and research the relationship between the topological basis states and the ground states. In order to study the Hamiltonian system beyond XXZ model, we introduce two Temperley-Lieb algebra generators and two other generalized generators. Then we investigate the relationship between topological basis and Heisenberg XXZ model with Dzyaloshinskii-Moriya interaction. The results show that the ground state of this model falls on the topological basis state for anti-ferromagnetic case and gapless phase case.     

Fidelity for States of Two Spin- $\frac{1}{2}$ Particles in Moving Frames

Fidelity for the spin part of states of two spin- particles is investigated from the viewpoint of moving observers. Using a numerical approach, the behavior of the fidelity in terms of the boost parameter is described for different amounts of spin entanglement and momentum entanglement. It is shown that for the spin entangled states the fidelity decreases less than that of the case of spin product states and there are special cases for which the fidelity remains perfect regardless of moving observers’ velocity. Generally, in the limit of boosts with speeds close to the speed of light, the fidelity saturates, i.e., it reaches to a constant value that depends on the amount of momentum entanglement and the width of the momentum distribution function.     

Prospects for production of ultracold $\mathsf{X^{1}\Sigma^{ + }}$ RbCs molecules

Recently, we have reported photoassociation of laser-cooled Rb and Cs atoms, decay of the RbCs photoassociation resonances to high levels of the state, and reexcitation to vibronic levels of the state [Kerman et al. , Phys. Rev. Lett. 92, 033004; 153001 (2004)]. Considering the reexcitation spectrum, we report here a preliminary analysis of perturbations in the c state by high levels of the and low levels of the state. Mixing with the B state provides the singlet character needed to stimulate decay to v = 0 of the ground state. We conclude that an experimental procedure that involves photoassociation of laser-cooled atoms, radiative decay, and stimulated Raman transfer to the ground electronic state is a feasible method for producing translationally, rotationally, vibrationally and electronically cold RbCs molecules. Electronic supplementary material to this article is available at and is accessible for authorized users. Received: 1 September 2004, Published online: 23 November 2004 PACS: 33.80.Ps Optical cooling of molecules; trapping - 34.50.Gb Electronic excitation and ionization of molecules; intermediate molecular states (including lifetimes, state mixing, etc.) - 33.20.Kf Visible spectra - 34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions - 33.15.Pw Fine and hyperfine structure A supplementary table (Tab. I) is only available in electronic form at http: //www.eurphysj.org     

Study of non-orthogonal Laguerre-L$\mathsf{^{2}}$ method for helium atom

We present a technique for describing solutions of the helium atom by using the non-orthogonal Laguerre-L² basis functions. The frozen-core approximation is used to calculate the helium energies. The completeness of helium wavefunctions obtained is studied in terms of weights of the Gaussian quadrature. The convergence of the energies is shown as the L² basis size increases and the completeness of the L² wave functions is also shown for different basis size.Received: 20 August 2003, Published online: 6 January 2004PACS: 34.80.Bm Elastic scattering of electrons by atoms and molecules - 34.80.Dp Atomic excitation and ionization by electron impact     

Surface second-harmonic generation in Au: TiO$\mathsf{_{2}}$ cermet thin films

The Surface Second-Harmonic Generation (SSHG) in Au: TiO₂ thin films of nanocermets is studied with samples of different metallic volume fractions using an IR Nd: YAG pulsed laser. We worked in a reflection geometry by varying the incidence angle and the directions of the incident beam polarization and of an analyzer of the Second Harmonic beam. We show that the SH signal is not due to electric dipolar processes only but can be treated within the general a, b, and d formalism where surfaces and bulk SH currents are well distinguished, and by describing the dielectric function of cermets within the effective-medium theory. The effective values obtained for a, b, and d are attributed to gold but the rather small discrepancies between them and those given by models are understandable by the fact that our samples are heterogeneous and not semi-infinite.Received: 19 March 2004, Published online: 6 July 2004PACS: 42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation - 78.66.-w Optical properties of specific thin films - 78.30.Ly Disordered solids     

Magnetic order in spin-1 and spin-$$\frac{3} {2}$$ interpolating square-triangle Heisenberg antiferromagnets

We consider coevolution of site state and network structures from different initial substrates: a one dimensional Ising chain, a scale free network and network with non-linear degree dependence. The dynamics is governed by a preassigned stability parameter S, and a rewiring factor φ, that determines whether the Ising spin at the chosen site flips or whether the site gets rewired to another site in the system. We have observed the steady state average stability and magnetisation for both kinds of systems to have an idea about the effect of initial network topology. Although the average stability shows almost similar behaviour, the magnetisation depends on the initial condition we start from. Apart from the local dynamics, the global effect on the dynamics has also been studied. These studies show interesting variations in the steady state values of average stability and magnetisation for different values of S and φ, which helps in indicating the gradual change of existing social networks.     

A model Hamiltonian for MgB $\mathsf{_{2}}$ which takes into account its unusual phononic features

Taking as a starting point the results of LDA calculations, which show that in the phonons have a strong quartic anharmonicity and that the bond-stretching electron-phonon interaction (EPI) has both a linear and a large quadratic component, we propose a model Hamiltonian which successfully matches a number of experimental evidences. We relate the single critical temperature for both superconducting gaps to a phonon-induced inter-band coupling whose amplitude increases with temperature. We also obtain phonon frequencies and linewidths depending on the band filling, as well as band energies and hybridization amplitudes depending on the phonon number.Received: 12 May 2003, Published online: 22 September 2003PACS: 74.20.-z Theories and models of superconducting state - 74.70.-b Superconducting materials     

Some New Entanglement-Assisted Quantum Error-Correcting MDS Codes with Length q 2 + 1 13 $\frac {q^{2}+1}{13}$

International Journal of Theoretical Physics - Entanglement-assisted quantum maximum distance separable (MDS) codes form a significant class of quantum codes. By using constacyclic codes, we...     

舰船噪声的$1 \\frac{1}{2}$维谱特征提取

证明了$1\\frac{1}{2}$维谱的几个基本性质,分析了由此产生的几种优良性能:可加强成整数倍谐波信号的基频分量,抑制高斯有色噪声及对称分布的噪声;剔除非二次相位耦合的谐波分量。在此基础上,将$1\\frac{1}{2}$维谱应用于舰船噪声的目标特征分析,提出井提取了7个特征量。经过神经网络分类器的分类识别,取得了较高的识别率:A类船的正确识别率为90%,B类船的为91.3%,C类船的为85.7%。     

Domain wall dynamics of the spin-$\frac{1}{2}$ Ising-like antiferromagnetic chain in presence of Dzyaloshinskii-Moriya interactions

We consider a one-dimensional Ising-like S = \frac12\frac{1}{2} Heisenberg antiferromagnetic Hamiltonian and study the dynamics of domain wall excitations in presence of both uniform and staggered Dzyaloshinskii-Moriya interactions. We obtain dispersion relations and dynamical spin correlation functions, S ^{x x} (q, ω) using the basis of domain wall pair states. It is shown that the line shapes of S ^{x x} (q, ω) are highly asymmetric over the whole Brillouin zone such that the spectral weights mainly concentrate in the low energy side. It is observed that presence of staggered Dzyaloshinskii-Moriya interaction explains the experimental results on the Ising-like antiferromagnetic compounds CsCoCl₃ and CsCoBr₃ very well.