Fermi-arc superconductivity, pseudogap and charge order in Bi2Sr2CaCu2O8+δ

We report STM/STS observations on the 4a×4a charge order in the pseudogap (PG) and superconducting (SC) states of Bi₂Sr₂CaCu₂O_8+δ, and suggest that the charge order is associated with incoherent quasiparticle or pair states around the antinodal fermi surface (FS), which are also responsible for the PG, and it can coexist with the superconductivity caused by the pairing of coherent quasiparticles on the nodal fermi arc. We also suggest that the nanometer-scale gap inhomogeneity in the SC state, reported previously [Pan, et al., Nature 413 (2001) 282; Mommo, et al., J. Phys. Soc. Jpn. 74 (2005) 2400; Hashimoto, et al., Phys. Rev. B74 (2006) 064508] arises from that in the PG state, which occurs around the antinodal FS.     

On the Doppler distortion of the sea-wave spectra

Discussions on a form of a frequency spectrum of wind-driven sea waves just above the spectral maximum have continued for the last three decades. In 1958 Phillips made a conjecture that wave breaking is the main mechanism responsible for the spectrum formation [O.M. Phillips, J. Fluid Mech. 4 (1958) 426]. That leads to the spectrum decay ∼ω⁻⁵, where ω is the frequency of waves. There is a contradiction between the numerous experimental data and this spectrum. Experiments frequently show decay ∼ω⁻⁴ [Y. Toba, J. Oceanogr. Soc. Japan 29 (1973) 209; M.A. Donelan, J. Hamilton, W.H. Hui, Phil. Trans. R. Soc. London A315 (1985) 509; P.A. Hwang, et al., J. Phys. Oceanogr. 30 (1999) 2753]. There are several ways of the explanation of this phenomenon. One of them (proposed by Banner [M.L. Banner, J. Phys. Oceanogr. 20 (1990) 966]) takes into account the Doppler effect due to surface circular currents generated by underlying waves in the Phillips model.In this article the influence of the Doppler effect on an arbitrary averaged spectrum is considered using both analytic and numerical approaches. Although we mostly concentrated on the very important case of Phillips model, the developed technique and general formula can be used for the analysis of other spectra.For the particular case of Phillips spectra we got analytic asymptotics in the vicinity of spectral maximum and for high frequencies. Results were obtained for two most important angular dependences of the spectra: isotropic and strongly anisotropic. Together with the analytic investigation we performed numerical calculations in a wide range of frequencies. Both high and low frequency asymptotics are in very good agreement with the numerical results.It was shown that at least at low frequencies, the correction to the spectrum due to the Doppler shift is negligible. At high frequencies there is an asymptotic with tail ∼ω⁻³.     

H2 dissociative adsorption at the armchair edges of graphite

We investigate and discuss how hydrogen behaves at the edges of a graphite sheet, in particular the armchair edge. Our density functional theory-based calculations results show that, in contrast to the zigzag edge [W.A. Diño, H. Nakanishi, H. Kasai, T. Sugimoto, T. Kondoe, e-J. Surf. Sci. Nanotech. 2 (2004) 77. [25]], regardless of orientation, there is an activation barrier hindering H₂ dissociation at the armchair edges. And once they do get dissociatively adsorbed at the armchair edges, we find that it would be extremely hard to desorb the H from their adsorption sites at the armchair edges. Furthermore, we also found that, consistent with our earlier conclusions [W.A. Diño, Y. Miura, H. Nakanishi, H. Kasai, T. Sugimoto, J. Phys. Soc. Jpn. 72 (2003) 1867. [24]], it is unlikely that we would find a whole H₂ in between plain graphite sheets.     

New class of T′-structure cuprate superconductors

High-temperature superconductivity has been discovered in La_2−xBa_xCuO₄ [J.G. Bednorz, K.A. Müller, Z. Phys. B 64 (1986) 189. [1]], a compound that derives from the undoped La₂CuO₄ crystallizing in the perovskite T-structure. In this structure oxygen octahedra surround the copper ions. It is common knowledge that charge carriers induced by doping in such an undoped antiferromagnetic Mott-insulator lead to high-temperature superconductivity [V.J. Emery, Phys. Rev. Lett. 58 (1987) 2794; C.M. Varma, S. Schmitt-Rink, E. Abrahams, Solid State Commun. 62 (1987) 681; E. Dagotto, Rev. Mod. Phys. 66 (1994) 763. [2], [3] and [4]]. The undoped material La₂CuO₄ is also the basis of the electron-doped cuprate superconductors [Y. Tokura, H. Takagi, S. Uchida, Nature (London) 337 (1989) 345. [5]] of the form La_2−xCe_xCuO_4+y [M. Naito, M. Hepp, Jpn. J. Appl. Phys. 39 (2000) L485; A. Sawa, M. Kawasaki, H. Takagi, Y. Tokura, Phys. Rev. B 66 (2002) 014531. [6] and [7]] which, however, crystallize in the so-called T′-structure, i.e. without apical oxygen above or below the copper ions of the CuO₂-plane. It is well known that for La_2−xCe_xCuO_4+y the undoped T′-structure parent compound cannot be prepared due to the structural phase transition back into the T-structure occurring around x∼0.05. Here, we report that if La is substituted by RE=Y, Lu, Sm, Eu, Gd, or Tb, which have smaller ionic radii but have the same valence as La, nominally undoped La_2−xRE_xCuO₄ can be synthesized by molecular beam epitaxy in the T′-structure. The second important result is that all these new T′-compounds are superconductors with fairly high critical temperatures up to 21 K. For this new class of cuprates La_2−xRE_xCuO₄, which forms the T′-parent compounds of the La-based electron doped cuprates, we have not been able to obtain the Mott-insulating ground state for small x before the structural phase transition into the T-structure takes place.     

Submillimeter-wave ESR measurements of Ca1−xCuO2 (x = 0.164) with edge-sharing CuO2 chains

Quasi-one-dimensional (1-D) cupric oxide Ca_1?xCuO₂ (x = 0.164) is the system with 25–40% hole-doped edge-sharing CuO₂ chains. However, the holes are almost localized in Ca_1?xCuO₂ and its magnetic susceptibility with a peak at 30 K was explained by the model considering both 1-D antiferromagnetic chains and spin dimers (Z. Hiroi, M. Okumura, Y. Nabeshima, T. Yamada, M. Takano: J. Phys. Soc. Jpn.69, 1824, 2000). To clarify the magnetic nature of Ca_1?xCuO₂, we performed submillimeter-wave electron spin resonance (ESR) measurements on a powder sample of Ca_0.83?6CuO₂. The resonance above 12 K showed typical powder ESR of Cu²⁺ and theg-values were determined to be g∥= 2.33 and g_⊥ = 2.06 from the analysis. The resonance below 12 K changed completely from ESR. The frequency-field relation of ESR at 1.8 K clearly showed the easy-axis type antiferromagnetic resonance.     

Synchronous vs asynchronous diffusion-reaction processes involving geminate radical pairs

We report lattice Monte Carlo calculations to study the efficiency of diffusion-controlled reactive processes involving geminate radical pairs. Whereas our earlier study [J.J. Kozak, C. Nicolis, G. Nicolis, N.J. Turro, J. Phys. Chem. 105 (2001) 10949] focused on factors affecting the reaction efficiency when a pair of coreactants moved synchronously on a surface modeled as a d=2 dimensional square planar lattice subject to periodic boundary conditions, we document here differences in reaction efficiency when a pair of coreactants can move synchronously or asynchronously on surfaces which are topologically different but characterized by the same number N of sites. As before, the first surface is taken to be a d=2 square planar lattice; the second surface considered is a Cartesian shell, the bounded surface of a cube. When studied as a function of system size, we find that synchronous dynamics are more efficient than asynchronous dynamics in optimizing diffusion-reaction processes; and, reactions on planar, periodic surfaces are more efficient than on cubic shells. The relevance of these conclusions to experimental studies on two radiation-induced, radical decay reactions [the one cited above and A.J. Frank, M. Grätzel, J.J. Kozak, J. Am. Chem. Soc. 98 (1976) 3317] is noted and discussed.     

Doublon–holon-binding mechanism of Mott transition in 2D Hubbard model

The mechanism of nonmagnetic Mott transitions in the Hubbard model on the square lattice is studied, using a variational Monte Carlo method. A simple doublon (D)–holon (H) binding mechanism a previous study proposed [J. Phys. Soc. Jpn. 75 (2006) 114706] has to be modified, because even a wave function with completely bound D–H pairs brings about a Mott transition at a finite correlation strength. By introducing two characteristic lengths, D–H pair binding length, ξ_DH, and minimum inter-doublon distance, ξ_DD, we can properly describe the physics of Mott transitions, and determine the critical point by ξ_DD ～ ξ_DH. This concept seems universal, because it is valid not only for newly introduced wave functions with long-range D–H and D–D (H–H) correlation factors discussed here, but for a wide range of wave functions with D–H binding factors.     

An atomistic approach to the dielectric modes of BaTiO3 and SrTiO3

Recently, a clear long-sought Debye mode (D) in barium titanate (BT) was identified [J. Hlinka, T. Ostapchuk, D. Nuzhnyy, J. Petzelt, P. Kuzel, C. Kadlec, P. Vanek, I. Ponomareva, L. Bellaiche, Phys. Rev. Lett. 101 (2008) 167402] and this mode was shown to originate from the polar coordinate that also generates the so-called Slater mode (S). The inter-relations between the D mode and the normal A1-type phonon modes were studied by those authors using a four-mode phenomenological model. The present work is to offer an atomistic support of their work and to better illustrate the nature of and the couplings between these modes. In addition, we extend the as-obtained insights to the investigation of the nature of the low frequency Raman peaks that were found in ¹⁸O-substituted strontium titanate (ST) many years ago [M. Itoh, R. Wang, Y. Inaguma, T. Yamaguchi, Y.-J. Shan, T. Nakamura, Phys. Rev. Lett. 82 (1999) 3540]. Thus, our work provides important information on the connections between the lattice dynamics of BT and ST.     

Asymmetrically doped one-dimensional trans-polymers

More than 30 years ago [H. Shirakawa, E.J. Louis, A.G. MacDiarmid, C.K. Chiang, A.J. Heeger, J. Chem. Soc. Chem. Comm. 578 (1977); S. Etemad, A.J. Heeger, Ann. Rev. Phys. Chem. 33 (1982) 443] it was discovered that doped trans-polyacetylene (CH)_x, a one-dimensional (1D) conjugated polymer, exhibits electrical conductivity. In this work we show that an asymmetrically doped 1D trans-polymer has non-conventional properties, as compared to symmetrically doped systems. Depending on the level of asymmetry between the chemical potentials of the two involved fermionic species, the polymer can be in a partially or fully spin polarized state. Some possible experimental consequences of doped 1D trans-polymers used as 1D organic polarized conductors are discussed.     

Dynamic phase transition in the kinetic spin-2 Blume–Emery–Griffiths model in an oscillating field

We extend our recent paper [M. Keskin, O. Canko, M. Erta?, J. Exp. Theor. Phys. (Sov. Phys. JETP) 105 (2007) 1190.] to present a study, within a mean-field approach, the stationary states of the kinetic spin-2 Blume–Emery–Griffiths model in the presence of a time-dependent oscillating magnetic field by using the Glauber-type of stochastic dynamics. We found 20 fundamental types of dynamic phase diagrams where exhibit more complex and richer phase diagrams than our recent paper. Especially, the obtained dynamic phase diagrams show the dynamic triple, quadruple and dynamic double critical end points besides dynamic tricritical points that depending on interaction parameters. The phase diagrams also exhibit a disordered (d) and the ferromagnetic-2 (f₂) phases, and the f₂+d, f₂+fq, fq+d, f₂+f₁+fq and f₂+fq+d, where f₁ are fq the ferromagnetic-1 and ferroquadrupolar or simply quadrupolar phases respectively, coexistence phase regions that strongly depend on interaction parameters.     

Hyperquadratic plasmon dispersion in indium

Experimental evidence suggested that the plasmon dispersion in aluminum has two branches with a discontinuous slope change at low momentum. In a recent experiment with high momentum resolution [J. Sprösser-Prou, A. vom Felde and J. Fink, Phys. Rev. B, 40 (1989) 5799] this discontinuity could not be found. For indium, the dielectric behavior of which closely resembles that of a free electron gas, there are only two experiments, both reporting a discontinuous slope change [T. Aiyama and K. Yada, J. Phys. Soc. Jpn., 38 (1975) 1357. T. Bornemann, J. Eickmans and A. Otto, Solid State Commun., 65 (1988) 381]. We could not find such a discontinuity for indium; on the contrary, the dispersion is hyperquadratic, similar to the findings of Sprösser-Prou et al. for aluminum.     

Antiferromagnetic resonance in Bi2CuO4

Magnetic resonance of the low-frequency spin-wave branch in the Bi₂CuO₄ antiferromagnet with an easy-plane anisotropy has been studied. Angular, frequency, and temperature dependences of the position and width of the antiferromagnetic resonance (AFMR) line have been measured. Our measurements combined with earlier data [H. Ochta, K. Yoshida, T. Matsuya, T. Nanba, M. Motokawa, K. Yamada, Y. Endon, and S. Hosoya, J. Phys. Soc. Jpn. 61, 2921 (1992); E. W. Ong, G. H. Kwei, R. A. Robinson, B. L. Ramakrishna, and R. B. von Dreele, Phys. Rev. B 42, 4255 (1990) [ have allowed us to determine anisotropy constants of this material and to account for the unusual character of its static susceptibility anisotropy. The AFMR line shifts to the high-field side and broadens in a temperature range of 10–15 K, and the cause of this has remained unclear. In the low-temperature range the line shows a hysteresis corresponding to a static field magnitude several times as large as the spin-flop field. The position and width of the AFMR line depend sensitively on the sample preparation technique. Zh. éksp. Teor. Fiz. 113, 2244–2255 (June 1998)     

The determinant representation of an N-fold Darboux transformation for the short pulse equation

We present an explicit representation of an N-fold Darboux transformation T?_N for the short pulse equation, by the determinants of the eigenfunctions of its Lax pair. In the course of the derivation of T?_N, we show that the quasi-determinant is avoidable, and it is contrast to a recent paper (J. Phys. Soc. Jpn. 81 (2012), 094008) by using this relatively new tool which was introduced to study noncommutative mathematical objectives. T?_N produces new solutions u^[N] and x^[N] which are expressed by ratios of two corresponding determinants. We also obtain the soliton solutions, which have a variable trajectory, of the short pulse equation from new “seed” solutions.     

A redefined anharmonic potential energy surface of HCN

A set of cubic and quartic anharmonic potential constants, k_ijl, k_ijlm of the normal mode potential energy surface of H¹²C¹⁴N was determined by a least-squares analysis applied to 79 most recently observed values of the vibrational and rotational energies. The calculated constants are a second solution of the fitting besides that of T. Nakagawa and Y. Morino (Bull. Chem. Soc. Jpn., 42, 2212–2219 (1969)).     

Classical oscillator with position-dependent mass in a complex domain

We study complexified Harmonic Oscillator with a position-dependent mass, termed as Complex Exotic Oscillator (CEO). The complexification induces a gauge invariance [A.V. Smilga, J. Phys. A 41 (2008) 244026, arXiv:0706.4064; A. Mostafazadeh, J. Math. Phys. 43 (2002) 205; A. Mostafazadeh, J. Math. Phys. 43 (2002) 2814; A. Mostafazadeh, J. Math. Phys. 43 (2002) 3944]. The role of PT-symmetry is discussed from the perspective of classical trajectories of CEO for real energy. Some trajectories of CEO are similar to those for the particle in a quartic potential in the complex domain [C.M. Bender, S. Boettcher, P.N. Meisinger, J. Math. Phys. 40 (1999) 2201; C.M. Bender, D.D. Holm, D. Hook, J. Phys. A 40 (2007) F793, arXiv:0705.3893].     

Entanglement of Formation for Qubit-Qudit System Using Partition of Qudit System into a Set of Qubit System

Gerjuoy (Phys. Rev. A 67:052308, 2003) has derived a closed-form lower bound for the entanglement of formation of a mixed qubit-qudit system (qudit system has d levels with d≥3). In this paper, inspired by Gerjuoy’s method, we propose a scheme that partitions a qubit-qudit system into d(d?1)/2 qubit-qubit systems, which can be treated by all known methods pertinent to qubit-qubit system. The method is demonstrated by a qubit-qudit system (the levels of qudit are d=3 and d=5, respectively).     

Stochastic flows,reaction — Diffusion processes,and morphogenesis

Recently, anexact procedure has been introduced [C. A. Walsh and J. J. Kozak,Phys. Rev. Lett. 47:1500 (1981)] for calculating the expected walk length 〈n〉 for a walker undergoing random displacements on a finite or infinite (periodic)d-dimensional lattice with traps (reactive sites). The method (which is based on a classification of the symmetry of the sites surrounding the central deep trap and a coding of the fate of the random walker as it encounters a site of given symmetry) is applied here to several problems in lattice statistics for each of whichexact results are presented. First, we assess the importance of lattice geometry in influencing the efficiency of reaction-diffusion processes in simple and multiple trap systems by reporting values of 〈n〉 for square (cubic) versus hexagonal lattices ind=2, 3. We then show how the method may be applied to variable-step (distance-dependent) walks for a single walker on a given lattice and also demonstrate the calculation of the expected walk length 〈n〉 for the case of multiple walkers. Finally, we make contact with recent discussions of “mixing” by showing that the degree of chaos associated with flows in certain lattice systems can be calibrated by monitoring the lattice walks induced by the Poincaré map of a certain parabolic function.     

An all-silicon linear chain NMR quantum computer

An updated version of our all-silicon quantum computing scheme [T.D. Ladd, J.R. Goldman, F. Yamaguchi, Y. Yamamoto, E. Abe, K.M. Itoh, Phys. Rev. Lett. 89 (2002) 017901. [3]] and the experimental progress towards its realization are discussed. We emphasize the importance of revisiting a wide range of isotope effects which have been explored over the past several decades for the construction of solid-state silicon quantum computers. Using RF decoupling techniques [T.D. Ladd, D. Maryenko, Y. Yamamoto, E. Abe, K.M. Itoh, Phys. Rev. B. 71 (2005) 014401] phase decoherence times T₂=25 s of ²⁹Si nuclear spins in single-crystal Si have been obtained at room temperature. We show that a linear chain of ²⁹Si stable isotopes with nuclear spin I=1/2 embedded in a spin free ²⁸Si stable isotope matrix can form an ideal building block for solid-state quantum information processors, especially, in the form of a quantum memory which requires a large number of operations within T₂ for the continuous error correction.     

Quantum entanglement formation by repeated spin blockade measurements in a spin field-effect transistor structure embedded with quantum dots

We propose a method of operating a quantum state machine made of stacked quantum dots buried in adjacent to the channel of a spin field-effect transistor (FET) [S. Datta, B. Das, Appl. Phys. Lett. 56 (1990) 665; K. Yoh, et al., Proceedings of the 23rd International Conference on Physics of Semiconductors (ICPS) 2004; H. Ohno, K. Yoh et al., Jpn. J. Appl. Phys. 42 (2003) L87; K. Yoh, J. Konda, S. Shiina, N. Nishiguchi, Jpn. J. Appl. Phys. 36 (1997) 4134]. In this method, a spin blockade measurement extracts the quantum state of a nearest quantum dot through Coulomb blockade [K. Yoh, J. Konda, S. Shiina, N. Nishiguchi, Jpn. J. Appl. Phys. 36 (1997) 4134; K. Yoh, H. Kazama, Physica E 7 (2000) 440] of the adjacent channel conductance. Repeated quantum Zeno-like (QZ) measurements [H. Nakazato, et al., Phys. Rev. Lett. 90 (2003) 060401] of the spin blockade is shown to purify the quantum dot states within several repetitions. The growth constraints of the stacked InAs quantum dots are shown to provide an exchange interaction energy in the range of 0.01–1 meV [S. Itoh, et al., Jpn. J. Appl. Phys. 38 (1999) L917; A. Tackeuchi, et al., Jpn. J. Appl. Phys. 42 (2003) 4278]. We have verified that one can reach the fidelity of 90% by repeating the measurement twice, and that of 99.9% by repeating only eleven QZ measurements. Entangled states with two and three vertically stacked dots are achieved with the sampling frequency of the order of 100 MHz.     

Effects of next-nearest-neighbor hopping interaction on polaron excitations in pernigraniline-base

The role of next-nearest-neighbor hopping interaction in determining the band structures and lattice configurations of combined polarons in pernigraniline-base polymer is explored on the basis of the Baranowski-Büttner-Voit (BBV) model. Numerical calculations show that the valence band extends to a larger range while the conduction band acts to the contrary, as the strength of the next-nearest-neighbor hopping interaction increases. The width of the Peierls gap and the number of the bound states trapped in have almost no changes. If the coupling strength β<0.15, the transition energy from the lower gap level to the higher one for a combined electron-polaron matches the long-lived 1.5 eV photoinduced absorption peak [J.M. Leng, R.P. McCall, K.R. Cromack, Y. Sun, S.K. Manohar, A.G. MacDiarmid, A.J. Epstein, Phys. Rev. B 48 (1993) 15719], and also supports the high temperature dispersion in the thermally stimulated depolarization current (TSDC) experiment [A.N. Papathanassiou, J. Grammatikakis, S. Sakkopoulos, E. Vitoratos, E. Dalas, J. Phys. Chem. Solids 63 (2002) 1771]. For a combined hole-polaron, new shallow level emerges when β∼0.12.