Magnetic fluctuations in coupled inequivalent Hubbard layers as a model for Y2Ba4Cu7O15
Institut für Theoretische Physik, Universität Würzburg, Am
Hubland, 97074 Würzburg, Germany
2 Department of Physics, University of Illinois at Urbana-Champaign, 1110 W. Green Street, Urbana 61801 IL, USA
Published online: 15 March 1999
We investigate, within the fluctuation-exchange approximation, a correlated-electron model for represented by two inequivalent Hubbard layers coupled by an interlayer hopping . An energy offset δ is introduced in order to produce a different charge carrier concentration in the two layers. We compare several single-particle and magnetic excitations, namely, the single particle scattering rate, the spectral function and the spin lattice as well as spin-spin relaxation times in the two layers as a function of δ. We show that the induced interlayer magnetic coupling produces a tendency to "equalization" of the magnetic properties in the two layers whereby antiferromagnetic fluctuations are suppressed in the less doped layer and enhanced in the heavily doped one.The strong antiferromagnetic bilayer coupling causes the charge carriers in the plane with larger doping concentration to behave similar to those of the underdoped layer, they are coupled to. This effect grows for decreasing temperature. For high temperatures or if both layers are optimally or overdoped, i.e. when the antiferromagnetic correlation length becomes of the order or smaller than one lattice site the charge carrier and magnetic dynamics of the two layers is disconnected and the equalization effect disappears. These results are in good agreement with NMR experiments on by Stern et al. [Phys. Rev B 51, 15478 (1995)]. We also compare the results with calculations on bilayer systems with equivalent layers as models for the constituent compounds and .
PACS: 74.72.h – High-Tc compounds / 71.27.+a – Strongly correlated electron systems; heavy fermions / 76.60.k – Nuclear magnetic resonance and relaxation
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1999