Fermi arc in doped high-Tc cuprates

We propose a $d$-density wave induced by the spin-orbit coupling in the CuO plane. The spectral function of high-temperature superconductors in the under doped and lightly doped regions is calculated in order to explain the Fermi arc spectra observed recently by angle-resolved photoemission spectroscopy. We take into account the tilting of CuO octahedra as well as the on-site Coulombrepulsive interaction; the tilted octahedra induce the staggered transfer integral between $p_{x,y}$ orbitals and Cu $t_{2g}$ orbitals, and bring about nontrivial effects of spin-orbit coupling for the $d$ electrons in the CuO plane. The spectral weight shows a peak at around ($\pi/2$,$\pi/2$) for light doping and extends around this point forming an arc as the carrier density increases, where the spectra for light doping grow continuously to be the spectra in the optimally doped region. This behavior significantly agrees with that of the angle-resolved photoemissionspectroscopy spectra. Furthermore, the spin-orbit term and staggered transfer effectively induce a flux state, a pseudo-gap with time-reversal symmetry breaking. We have a nodal metallic state in the light-doping case since the pseudogap has a $d_{x^2-y^2}$ symmetry.Comment: 5 pages, 7 figure

Signaling Pathways Crucial for Craniofacial Development Revealed by Endothelin-A Receptor-Deficient Mice

AbstractMost of the bone and cartilage in the craniofacial region is derived from cephalic neural crest cells, which undergo three primary developmental events: migration from the rhombomeric neuroectoderm to the pharyngeal arches, proliferation as the ectomesenchyme within the arches, and differentiation into terminal structures. Interactions between the ectomesenchymal cells and surrounding cells are required in these processes, in which defects can lead to craniofacial malformation. We have previously shown that the G-protein-coupled endothelin-A receptor (ETA) is expressed in the neural crest-derived ectomesenchyme, whereas the cognate ligand for ETA, endothelin-1 (ET-1), is expressed in arch epithelium and the paraxial mesoderm-derived arch core; absence of either ETA or ET-1 results in numerous craniofacial defects. In this study we have attempted to define the point at which cephalic neural crest development is disrupted in ETA-deficient embryos. We find that, while neural crest cell migration in the head of ETA−/− embryos appears normal, expression of a number of transcription factors in the arch ectomesenchymal cells is either absent or significantly reduced. These ETA-dependent factors include the transcription factorsgoosecoid, Dlx-2, Dlx-3, dHAND, eHAND, and Barx1, but not MHox, Hoxa-2, CRABP1, or Ufd1. In addition, the size of the arches in E10.5 to E11.5 ETA−/− embryos is smaller and an increase in ectomesenchymal apoptosis is observed. Thus, ETA signaling in ectomesenchymal cells appears to coordinate specific aspects of arch development by inducing expression of transcription factors in the postmigratory ectomesenchyme. Absence of these signals results in retarded arch growth, defects in proper differentiation, and, in some mesenchymal cells, apoptosis. In particular, this developmental pathway appears distinct from the pathway that includesUFD1L, implicated as a causative gene in CATCH 22 patients, and suggests parallel complementary pathways mediating craniofacial development

Spectral Classification and Effective Temperatures of L and T Dwarfs Based of Near-Infrared Spectra

We have obtained near-infrared spectra of L dwarfs, L/T transition objects and T dwarfs using Subaru. Resulting spectra are examined in detail to see their dependence on the spectral types. We have obtained bolometric luminosities of the objects with known parallaxes in our sample, first by integrating the spectra and second by K band bolometric correction. We derive the relation between effective temperature and spectral type.Comment: To appear in May 20, 2004 issue of ApJ There is a companion paper by Tsuji, Nakajima and Yanagisaw

Off-diagonal Wave Function Monte Carlo Studies of Hubbard Model I

We propose a Monte Carlo method, which is a hybrid method of the quantum Monte Carlo method and variational Monte Carlo theory, to study the Hubbard model. The theory is based on the off-diagonal and the Gutzwiller type correlation factors which are taken into account by a Monte Carlo algorithm. In the 4x4 system our method is able to reproduce the exact results obtained by the diagonalization. An application is given to investigate the half-filled band case of two-dimensional square lattice. The energy is favorably compared with quantum Monte Carlo data.Comment: 9 pages, 11 figure

Quantum Monte Carlo diagonalization for many-fermion systems

In this study we present an optimization method based on the quantum Monte Carlo diagonalization for many-fermion systems. Using the Hubbard-Stratonovich transformation, employed to decompose the interactions in terms of auxiliary fields, we expand the true ground-state wave function. The ground-state wave function is written as a linear combination of the basis wave functions. The Hamiltonian is diagonalized to obtain the lowest energy state, using the variational principle within the selected subspace of the basis functions. This method is free from the difficulty known as the negative sign problem. We can optimize a wave function using two procedures. The first procedure is to increase the number of basis functions. The second improves each basis function through the operators, $e^{-\Delta\tau H}$, using the Hubbard-Stratonovich decomposition. We present an algorithm for the Quantum Monte Carlo diagonalization method using a genetic algorithm and the renormalization method. We compute the ground-state energy and correlation functions of small clusters to compare with available data

Magnetic-Field-Independent Ultrasonic Dispersions in the Magnetically Robust Heavy Fermion System SmOs4Sb12

Elastic properties of the filled skutterudite compound SmOs$_4$Sb$_{12}$ have been investigated by ultrasonic measurements. The elastic constant $C_{11}(\omega)$ shows two ultrasonic dispersions at $\sim$15 K and $\sim$53 K for frequencies $\omega$ between 33 and 316 MHz, which follow a Debye-type formula with Arrhenius-type temperature-dependent relaxation times, and remain unchanged even with applied magnetic fields up to 10 T. The corresponding activation energies were estimated to be $E_2$ = 105 K and $E_1$ = 409 K, respectively. The latter, $E_1$, is the highest value reported so far in the Sb-based filled skutterudites. The presence of magnetically robust ultrasonic dispersions in SmOs$_4$Sb$_{12}$ implies a possibility that an emergence of a magnetically insensitive heavy fermion state in this system is associated with a novel local charge degree of freedom which causes the ultrasonic dispersion.Comment: 5 pages, 4 figure

Madelung Energy of the Valence Skipping Compound BaBiO3_3

Several elements show valence skip fluctuation, for instance, Tl forms the compounds in valence states +1 and +3, and Bi forms in +3 and +5 states. This kind of fluctuation gives rise to a negative effective attractive interaction and the Kondo effect. In the compounds of valence skipping elements, the carrier doping will induce superconductivity with high critical temperature. For example, Ba$_{1-x}$K$_x$BiO$_3$ shows high $T_c$ which is unlikely from the conventional electron-phonon mechanism. The reason for the missing of some valence states in such valence skip compounds remains a mystery. We have performed the evaluation of the Madelung potential for BaBiO$_3$, and have shown for the first time that charge-ordered state is stabilized if we take into account the polarization of the oxygen charge. We argue that the effective Coulomb interaction energy $U$ may be negative evaluating the local excitation energy