International Journal of Modern Physics B

Six months ago, I was asked to write a personal history of my engagement with the high-T_c problem of the cuprate superconductors, in a rather informal and autobiographical style. As the work proceeded, I realized that it was impossible and would have been dishonest to separate out my rather amusing but seminal early fumblings from the complete restructuring of the problem which I have achieved during the past decade. But the result became considerably too long, by over half, for its intended recipient. The assignment had left me with no obligation to deal with all the fascinating but irrelevant phenomenology which I had more or less instinctively ignored on my way, but that feature also fails to endear the article to any conceivable editorial board containing knowledgeable experts on the subject. Also, their purpose was for it to serve as an "introduction to the more technical debates", but its message is that almost all of these are not relevant. They are not, on the whole, focused on achieving understanding of the crucial experimental anomalies, many, if not most, of which are now understood. The key to the problem is a new method of dealing with the constrained Hilbert space which follows from the necessity of Gutzwiller projection.

This work investigates a d-p Hubbard model by the n-pole approximation in the hole-doped regime. In particular, the spectral function A(ω, k) is analyzed varying the filling, the local Coulomb interaction and the d-p hybridization. It should be remarked that the original n-pole approximation (Phys. Rev.184, 451 1969) has been improved in order to include adequately the k-dependence of the important correlation function 〈S_j·S_i〉 present in the poles of the Green's functions. It has been verified that the topology of the Fermi surface (defined by A(ω = 0, k)) is deeply affected by the doping, the strength of the Coulomb interaction and also by the hybridization. Particularly, in the underdoped regime, the spectral function A(ω = 0, k) presents very low intensity close to the antinodal points (0, ±π) and (±π, 0). Such a behavior produces an anomalous Fermi surface (pockets) with pseudogaps in the region of the antinodal points. On the other hand, if the d-p hybridization is enhanced sufficiently, such pseudogaps vanish. It is precisely the correlation function 〈S_j·S_i〉, present in the poles of the Green's functions, plays an important role in the underdoped situation. In fact, antiferromagnetic correlations coming from 〈S_j·S_i〉 strongly modify the quasiparticle band structure. This is the ultimate source of anomalies in the Fermi surface in the present approach.

The effects of structure nonuniformity and thermal perturbation on properties of proton conductivity in hydrogen-bonded systems with damping exposed in an externally applied electric-field have been numerically studied by fourth order Runge–Kutta method in our soliton model. The results obtained show that the proton-soliton is very robust against the structure disorder including the fluctuation of the force constant and disorder in the sequence of masses and thermal perturbation and damping effect of medium, its velocity of conductivity increases with increasing externally applied electric-field and with decreasing damping coefficient of medium, but the proton-soliton disperses at quite great fluctuations of force constant and damping coefficient. In the meantime, the proton-soliton in ice crystals is thermally stable in the region of temperature of T ≤ 273 K. From the numerical simulation, we find out that the mobility (or velocity) of proton conduction in ice is a nonmonotonic function of temperature in the temperature region of 170–273 K, i.e., it increases initially, reaches a maximum at about 191.4 K, subsequently decreases to a minimum at about 211.6 K, and then increases again. This changed rule of mobility obtained consists qualitatively with its experimental datum in ice in the same temperature region. Thus these results provide an evidence for the soliton excited in the hydrogen-bonded systems.

In this study, we have found a new random ordered phase in isotropic models with many-body interactions. Spin correlations between neighboring planes are rigorously shown to form a long-range order, namely coplanar spin-pair order, using a unitary transformation, and the phase transition of this new order has been analyzed on the bases of the mean-field theory and correlation identities. In the systems with regular 4-body interactions, the transition temperature T_c is obtained as T_c = (z-2)J/k_B, and the field conjugate to this new order parameter is found to be H². In contrast, the corresponding physical quantities in the systems with random 4-body interactions are given by and H⁴, respectively. Scaling forms of order parameters for regular or random 4-body interactions are expressed by the same scaling functions in the systems with regular or random 2-body interactions, respectively. Furthermore, we have obtained the nonlinear susceptibilities in the regular and random systems, where the coefficient χ_nl of H³ in the magnetization shows positive divergence in the regular model, while the coefficient χ₇ of H⁷ in the magnetization shows negative divergence in the random model.

In this article, the precursors of CaCu_xMn_3-xMn₄O₁₂(x = 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4) were synthesized using wet-chemistry technique, and then samples were sintered in pure oxygen flow at 850^°C and ambient pressure with KCl 10 wt% addition. The Rietveld refinements of powder X-ray diffraction patterns showed that all the samples were single phase with cubic symmetry, the space group . The lattice parameters a decreased with increasing Cu doping level x. The transport properties were characterized with DC four-probe technique. The results indicated that the crystal structure of samples were deformed and then influenced the transport properties of these manganese oxides. The MR ratios at 85 K and in the magnetic field of 5 Tesla increased with increasing x and reached the maximum at x = 1.0, then decreased with further increasing x. These results originated maybe from the intergrain tunneling of spin-polarized carriers and double-exchange effect.

The performance of organic thin film transistors (OTFTs) strongly depends on the surface states of the gate insulator. Top-contact (TC) OTFTs with modified gate insulator were demonstrated in this paper. The modified gate insulator layers consisted of SiO₂ as the gate insulator and OTS (octadecyltrichlorosilane) or PMMA (Poly (methyl methacylate)) as the modified layer. The devices with the modified layer had field-effect mobility larger than 10^-3cm²/Vs, which was twice that of the untreated OTFT. The on/off current ratio was increased one order of magnitude and reached more than 10⁴. The leakage current was decreased from 10^-9 A to 10^-10 A. The results demonstrate that using modified gate insulators can obviously improve the performance of the OTFTs.

A thin film transistor (TFT) characteristics measuring and bias stress applying system using an alternating current (AC) pulse sequence similar to a real driving pulse was developed to study the properties of hydrogenated amorphous-silicon (a-Si:H) TFTs under real operating conditions. Using this system, the application of a gate bias stress and the measurement of source-to-drain current were performed successfully. Degradation of the TFT transfer curve depended on the ratio of on time to off time for a fixed on time; a longer off time made the shift of threshold voltage V_TH smaller. In addition, degradation of transfer curves depended on the frequency of the driving pulse; a higher frequency pulse produced a larger degradation. These results could originate from the dependence of the direction of V_TH shift on the polarity of the gate bias, and the differences of injection barrier height and the mobility of the electron and hole. Using the AC driving pulse and the transient measurement system proposed in this study may be useful in understanding the response of TFTs under real operating conditions.

Giant magneto-impedance (GMI) effects were investigated in CuBe/CoNiP and CuBe/Insulator/CoNiP composite wires prepared by electroless deposition on pure or insulated CuBe wires. Experimental results show that the maximal GMI ratio and the field sensitivity of the composite wires are further improved by adding an insulator layer between the CuBe core and ferromagnetic layer. A distinct MI effect was observed in the composite wires with insulator even at low frequencies. MI ratio is about 18% at 20 kHz and 239% at 600 kHz. The maximal field sensitivity is 34%/Oe at 600 kHz. The properties of GMI in these composite wires are analyzed via complex permeability.

A study of variational wave functions for calculation of the ground-state energies of excitons confined in a two-dimensional (2D) disc-like and three-dimensional (3D) spherical parabolic GaAs quantum dots (QDs) is presented. We have used four variational trial wave functions constructed as the harmonic-oscillator basis multiplied by different correlation functions. The proposed correlation function formed by including linear expansion in terms of Hylleraas-like coordinates to the Jastrow factor is able to capture nearly exactly the ground-state energies of 3D excitons, and it properly account for the results of 2D excitons. Quantum Monte Carlo techniques combined with the proposed wave function are a powerful tool for studying excitons in parabolic QDs.

Five samples of mixed Y₂O₃/CaO doped ZrO₂ electrolytes, with the same nominal chemical composition of (ZrO₂)_0.90–(Y₂O₃)_0.04-( CaO)_0.06, were sintered at 1600^°C for 2, 4, 6, 8 and 10 h, respectively. The frequency dependence of the grain-boundary conductivity of each sample was measured using complex impedance method in the temperature range from 773 to 1073 K and experimental results were analyzed according to a power law, which was frequently referred to as the so-called universal dynamic response (UDR). Results indicated the apparent ac grain-boundary conductivity can be well-described by the power law and some useful information about the grain-boundary effect, such as the activation energy of the grain-boundary conduction and the dissociated energy of the charge carrier in the space charge layer, can be obtained by analyzing the temperature dependence of the power law parameters.

In this paper, we discuss the problem of heat exchange in a composite plane wall whose heat transmitting coefficient is a stationary random field. We present a method of multiscale asymptotic expansions and the corresponding finite element method to solve the problem.

Using the Oseen–Zöcher–Frank theory, in the steady state, I study the distortion energy of a disclination line in nematic liquid crystal in the presence of an external magnetic field. The director field around a disclination line is exactly calculated by minimizing the total free energy. The behavior of total free energy as a function of magnetic field for two kinds of nematic material (positive and negative magnetic anisotropy) are discussed. In the short distance limit, the total free energy per unit length is calculated. In this case, the magnetic dependence of total free energy is discussed.

We use the Density Matrix Renormalization Group and the Abelian bosonization method to study the effect of density on quantum phases of one-dimensional extended Bose–Hubbard model. We predict the existence of supersolid phase and also other quantum phases for this system. We have analyzed the role of extended range interaction parameters on solitonic phase near half-filling. We discuss the effects of dimerization in nearest neighbor hopping and interaction as well as next nearest neighbor interaction on the plateau phase at half-filling.