arXiv subjects

K. A. Hallberg

Publications and source records attributed to K. A. Hallberg.

4 recordsLinked to original sources

arXiv2013

Spin-spin correlations between two Kondo impurities coupled to an open Hubbard chain

In order to study the interplay between Kondo and Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, we calculate the spin-spin correlation functions between two Kondo impurities coupled to different sites of a half-filled open Hubbard chain. Using the density-matrix renormalization group (DMRG), we re-examine the exponents for the power-law decay of the correlation function between the two impurity spins as a function of the antiferromagnetic coupling J, the Hubbard interaction U, and the distance R between the impurities. The exponents for finite systems obtained in this work deviate from previously published DMRG calculations. We furthermore show that the long-distance behavior of the exponents is the same for impurities coupled to the bulk or to both ends of the chain. We note that a universal exponent for the asymptotic behavior cannot be extracted from these finite-size systems with open boundary conditions.

cond-mat.str-el↗

arXiv1995

Static and dynamical properties of a magnetic impurity in a strongly correlated electronic system

Using numerical techniques we study the zero temperature properties of a substitutional magnetic impurity in a one-dimensional correlated system described by the Hubbard model with repulsive interaction $U$. We find that, while the static spin correlation maintains a $2k_F$ periodicity, the charge correlations show Friedel oscillations with a $4k_F$ periodicity for large values of $U$. The static on-site susceptibility decreases as the interactions in the chain are turned on and we interpret this as an increase of the Kondo temperature. For large values of $U$ the short range antiferromagnetic correlations dominate over the collective Kondo singlet formation.

cond-mat↗

arXiv1995

Hole dynamics in generalized spin backgrounds in infinite dimensions

We calculate the dynamical behaviour of a hole in various spin backgrounds in infinite dimensions, where it can be determined exactly. We consider hypercubic lattices with two different types of spin backgrounds. On one hand we study an ensemble of spin configurations with an arbitrary spin probability on each sublattice. This model corresponds to a thermal average over all spin configurations in the presence of staggered or uniform magnetic fields. On the other hand we consider a definite spin state characterized by the angle between the spins on different sublattices, i.e a classical spin system in an external magnetic field. When spin fluctuations are considered, this model describes the physics of unpaired particles in strong coupling superconductors.

cond-mat↗

arXiv1995

Numerical renormalization group study of the correlation functions of the antiferromagnetic spin-$\frac{1}{2}$ Heisenberg chain

We use the density-matrix renormalization group technique developed by White \cite{white} to calculate the spin correlation functions $<{S}_{n+l}^z{S}_n^z>=(-1)^l ω(l,N)$ for isotropic Heisenberg rings up to $N=70$ sites. The correlation functions for large $l$ and $N$ are found to obey the scaling relation $ω(l,N)=ω(l,\infty)f_{XY}^α (l/N)$ proposed by Kaplan et al. \cite{horsch} , which is used to determine $ω(l,\infty)$. The asymptotic correlation function $ω(l,\infty)$ and the magnetic structure factor $S(q=π)$ show logarithmic corrections consistent with $ω(l,\infty)\sim a\sqrt{\ln{cl}}/l$, where $c$ is related to the cut-off dependent coupling constant $g_{eff}(l_0)=1/\ln(cl_0)$, as predicted by field theoretical treatments.

cond-mat↗