arXiv subjects

S. Maekawa

Publications and source records attributed to S. Maekawa.

132 records · Page 8Linked to original sources

arXiv1995

Heavy Quasiparticles in the Anderson Lattice Model

An exact-diagonalization technique on small clusters is used to study the dynamics of the one-dimensional symmetric Anderson lattice model. Our calculated excitation spectra reproduce key features expected for an infinite Kondo lattice such as nearly localized low-energy spin excitations and extended regions of `heavy-quasiparticle' bands. We show that, in contrast to the hybridization picture, low-energy spin excitations of the nearly-localized $f$-electron system play a key role in the formation of an almost dispersionless low-energy band of heavy quasiparticles.

cond-mat↗

arXiv1995

Brownian motion of Massive Particle in a Space with Curvature and Torsion and Crystals with Defects

We develop a theory of Brownian motion of a massive particle, including the effects of inertia (Kramers' problem), in spaces with curvature and torsion. This is done by invoking the recently discovered generalized equivalence principle, according to which the equations of motion of a point particle in such spaces can be obtained from the Newton equation in euclidean space by means of a nonholonomic mapping. By this principle, the known Langevin equation in euclidean space goes over into the correct Langevin equation in the Cartan space. This, in turn, serves to derive the Kubo and Fokker-Planck equations satisfied by the particle distribution as a function of time in such a space. The theory can be applied to classical diffusion processes in crystals with defects.

cond-mat↗

arXiv1995

Ground state properties and dynamics of the bilayer t-J model

We present an exact diagonalization study of bilayer clusters of t-J model. Our results indicate a crossover between two markedly different regimes which occurs when the ratio J_perp/J between inter-layer and intra-layer exchange constants increases: for small J_perp/J the data suggest the development of 3D antiferromagnetic correlations without appreciable degradation of the intra-layer spin order and the d_(x2-y2) hole pairs within the planes persist. For larger values of J_perp/J local singlets along the inter-layer bonds dominate, leading to an almost complete suppression of the intra-layer spin correlation and the breaking of the intra-layer pairs. The ground state with two holes in this regime has s-like symmetry. The data suggest that the crossover may occur for values of J_perp/J as small as 0.2. We present data for static spin correlations, spin gap, and electron momentum distribution and spectral function of the `inter-layer RVB state' realized for large J_perp/J. The latter deviates from the single layer ground state, making it an implausible candidate for modelling high-temperature superconductors.

cond-mat↗

arXiv1995

Anomalous Spin and Charge Dynamics of the 2D t-J Model at low doping

We present an exact diagonalization study of the dynamical spin and density correlation function of the 2D t-J model for hole doping < 25%. Both correlation functions show a remarkably regular, but completely different scaling behaviour with both hole concentration and parameter values: the density correlation function is consistent with that of bosons corresponding to the doped holes and condensed into the lowest state of the noninteracting band of width 8t, the spin correlation function is consistent with Fermions in a band of width J. We show that the spin bag picture gives a natural explanation for this unusual behaviour.

cond-mat↗

arXiv1994

Bogoliubov Quasiparticle Excitations in the Two-Dimensional t-J Model

Using a proposed numerical technique for calculating anomalous Green's functions characteristic of superconductivity, we show that the low-lying excitations in a wide parameter and doping region of the two-dimensional $t$$-$$J$ model are well described by the picture of dressed Bogoliubov quasiparticles in the BCS pairing theory. The pairing occurs predominantly in $d_{x^2-y^2}$-wave channel and the energy gap has a size $Δ_d$$\simeq$$0.15J$$-0.27J$ between quarter and half fillings. Opening of the superconducting gap in the photoemission and inverse-photoemission spectrum is demonstrated.

cond-mat↗

arXiv1993

Gutzwiller wavefunction in the three-band Hubbard model: A variational Monte Carlo study

The Gutzwiller wave function for the three-band Hubbard model on a two dimensional CuO$_2$ plane is studied by using the variational Monte Carlo (VMC) method in the limit $U_d \to \infty$, where $U_d$ is the Coulomb repulsion between holes on a Cu site. The VMC results for the energy and the fraction of $d$-holes are compared with those of the Rice-Ueda type Gutzwiller approximation (GA). The difference between the VMC and the GA results are most pronounced at half-filling, and away from half-filling the two results agree well in both the hole-doped and the electron-doped cases. The doping dependence of the momentum distribution function is also studied.

cond-mat↗