Multiperiodic magnetic structures in Hubbard superlattices

TL;DR

This paper investigates magnetic structures in one-dimensional Hubbard superlattices using DMRG, revealing four distinct magnetic regimes and oscillatory behaviors of SDW periods related to electronic density and layer thickness.

Contribution

It identifies four magnetic regimes in Hubbard superlattices and describes how SDW periods oscillate with electronic density and spacer thickness, extending understanding of magnetic behavior in these systems.

Findings

Four magnetic regimes identified in superlattices.

SDW wave vectors oscillate with electronic density.

SDW periods oscillate with spacer thickness, akin to exchange oscillations.

Abstract

We consider fermions in one-dimensional superlattices (SL's), modeled by site-dependent Hubbard-U couplings arranged in a repeated pattern of repulsive (i.e., U>0) and free (U=0) sites. Density Matrix Renormalization Group (DMRG) diagonalization of finite systems is used to calculate the local moment and the magnetic structure factor in the ground state. We have found four regimes for magnetic behavior: uniform local moments forming a spin-density wave (SDW), `floppy' local moments with short-ranged correlations, local moments on repulsive sites forming long-period SDW's superimposed with short-ranged correlations, and local moments on repulsive sites solely with long-period SDW's; the boundaries between these regimes depend on the range of electronic densities, rho, and on the SL aspect ratio. Above a critical electronic density, rho_{uparrow downarrow}, the SDW period oscillates both with rho and with the spacer thickness. The former oscillation allows one to reproduce all SDW wave vectors within a small range of electronic densities, unlike the homogeneous system. The latter oscillation is related to the exchange oscillation observed in magnetic multilayers. A crossover between regimes of `thin' to `thick' layers has also been observed.