One-dimensional Kondo lattice at partial band filling

An effective Hamiltonian for the localized spins in the one-dimensional Kondo lattice model is derived via a unitary transformation involving a bosonization of delocalized conduction electrons. The effective Hamiltonian is shown to reproduce all the features of the model as identified in various numerical simulations, and provides much new information on the ferro- to paramagnetic phase transition and the paramagnetic phase.Comment: 11 pages Revtex, 1 Postscript figure. To appear in Phys. Rev. Let

Bound states in d-density-wave phases

We investigate the quasiparticle spectrum near surfaces in a two-dimensional system with d-density-wave order within a mean-field theory. For Fermi surfaces with perfect nesting for the ordering wave vector of the d-density-wave, a zero energy bound state occurs at [110] surfaces, in close analogy with the known effect in d-wave superconducting states or graphite. When the shape of the Fermi surface is changed by doping, the bound state energy moves away from the Fermi level. Furthermore, away from half-filling we find inhomogeneous phases with domain walls of the d-density-wave order parameter. The domain walls also support low energy bound states. These phenomena might provide an experimental test for hidden d-density-wave order in the high-Tc cuprates.Comment: 6 pages, 5 figure

Local Moments Coupled to a Strongly Correlated Electron Chain

A 1D model hamiltonian that is motivated by the recent discovery of the heavy-fermion behavior in the cuprates of the $Nd_2CuO_4$ type is studied. It consists of $t-J$ interacting conduction electrons coupled to a lattice of localized spins through a Kondo exchange term $J_K$. Exact diagonalization and density matrix renormalization group methods are used. The latter method is generalized to arbitrary densities. At half-filling, a spin gap opens for all $J_K>0$. Away from half-filling$,$ it is shown that, at strong $J_K$% , the ground state is an unsaturated ferromagnet . At weak $J_K$ the system is in a paramagnetic phase with enhanced RKKY correlations. The importance of self-screening of the local moments in the depletion regime is discussed. We argue that these findings transcend the specifics of the model.Comment: 10 pages, Latex, 4 figures included, to be published in PRB (Rapid Communications

Asymmetric magnetic interference patterns in 0-pi Josephson junctions

We examine the magnetic interference patterns of Josephson junctions with a region of 0- and of pi-phase shift. Such junctions have recently been realized as c-axis YBCO-Pb junctions with a single twin boundary in YBCO. We show that in general the junction generates self-fields which introduces an asymmetry in the critical current under reversal of the magnetic field. Numerical calculations of these asymmetries indicate they account well for the unexplained features observed in single twin boundary junctions.Comment: 4 pages, 3 figure

Low-Temperature Scaling Regime of Random Ferromagnetic-Antiferromagnetic Spin Chains

Using the Continuous Time Quantum Monte Carlo Loop algorithm, we calculate the temperature dependence of the uniform susceptibility, and the specific heat of a spin-1/2 chain with random antiferromagnetic and ferromagnetic couplings, down to very low temperatures. Our data show a consistent scaling behavior in both quantities and support strongly the conjecture drawn from the approximative real-space renormalization group treatment. A statistical analysis scheme is developed which will be useful for the search scaling behavior in numerical and experimental data of random spin chains.Comment: 4 pages and 3 figure

Spontaneous flux in a d-wave superconductor with time-reversal-symmetry-broken pairing state at {110} boundaries

The induction of an s-wave component in a d-wave superconductor is considered. Near the {110}-oriented edges of such a sample, the induced s-wave order parameter together with d-wave component forms a complex combination d+e^{i\phi} s, which breaks the time reversal symmetry (BTRS) of the pairing state. As a result, the spontaneous current is created. We numerically study the current distribution and the formation of the spontaneous flux induced by the current. We show that the spontaneous flux formed from a number of defect lines with {110} orientation has a measurable strength. This result may provide a unambiguous way to check the existence of BTRS pairing state at {110}-oriented boundaries.Comment: 4 pages, 2 ps-figures, content changed, references adde

Nonvanishing Local Moment in Triplet Superconductors

The Kondo effect in a $p_x + {\rm i} p_y$-wave superconductor is studied by applying the Wilson's numerical renormalization group method. In this type of superconductor with a full energy gap like a s-wave one, the ground state is always a spin doublet, while a local spin is shrunk by the Kondo effect. The calculated magnetic susceptibility indicates that the spin of the ground state is generated by the orbital effect of the $p_x + {\rm i} p_y$-wave Cooper pairs. The effect of spin polarization of the triplet superconductor is also discussed.Comment: 5 pages, 4 figures, to be published in J. Phys. Soc. Jp

Effects of Nonmagnetic Impurity Doping on Spin Ladder System

Effects of nonmagnetic impurity doping on an AF spin-1/2 Heisenberg ladder system are studied by the QMC method. A single nonmagnetic impurity induces a localized spin-1/2 moment accompanied by "static" and enhanced AF correlations around it. Small and finite concentration of impurities induces a remarkable change of magnetic and thermodynamic properties with gapless excitations. It also shows rather sharp but continuous crossover around the concentration of about 4%. Above the crossover concentration, all the spins are strongly coupled participating in the enhanced and rather uniform power-law decay of the antiferromagnetic correlation. Below the crossover, each impurity forms an antiferromagnetic cluster only weakly coupled each other. For random distribution of impurities, large Curie-like susceptibility accompanied with small residual entropy is obtained at low temperatures in agreement with recent experimental observation in Zn-doped $SrCu_{2}O_{3}$. Temperature dependence of AF susceptibility shows power-law-like but weaker divergence than the single chain AFH in the temperature range studied.Comment: 4 pages, LaTeX+epsf.sty, submitted to J.Phys.Soc.Jpn. New results of AF susceptibility are adde