6 research outputs found
Perturbation theories for the S=1/2 spin ladder with four-spin ring exchange
The isotropic S=1/2 antiferromagnetic spin ladder with additional four-spin
ring exchange is studied perturbatively in the strong coupling regime with the
help of cluster expansion technique, and by means of bosonization in the weak
coupling limit. It is found that a sufficiently large strength of ring exchange
leads to a second-order phase transition, and the shape of the boundary in the
vicinity of the known exact transition point is obtained. The critical exponent
for the gap is found to be , in agreement both with exact results
available for the dimer line and with the bosonization analysis. The phase
emerging for high values of the ring exchange is argued to be gapped and
spontaneously dimerized. The results for the transition line from strong
coupling and from weak coupling match with each other naturally.Comment: 8 pages, 4 figures, some minor changes in text and reference
Differences Between Hole and Electron Doping of a Two-Leg CuO Ladder
Here we report results of a density-matrix-renormalization-group (DMRG)
calculation of the charge, spin, and pairing properties of a two-leg CuO
Hubbard ladder. The outer oxygen atoms as well as the rung and leg oxygen atoms
are included along with near-neighbor and oxygen-hopping matrix elements. This
system allows us to study the effects of hole and electron doping on a system
which is a charge transfer insulator at a filling of one hole per Cu and
exhibits power law, d-wave-like pairing correlations when doped. In particular,
we focus on the differences between doping with holes or electrons.Comment: REVTEX 4, 10 pages, 13 figure
Two-Hole and Four-Hole Bound States in a t-J Ladder at half-filling
The two-hole excitation spectrum of the t-J ladder at half-filling is studied
using linked-cluster series expansion methods. A rich spectrum of bound states
emerges, particularly at small . Their dispersion relations and coherence
lengths are computed, along with the threshold behaviour as the bound states
merge into the continuum. A class of 4-hole bound states is also studied,
leading to the conclusion that phase separation occurs for ,
in agreement with other studies.Comment: revtex
The unusual electronic structure of the "pseudo-ladder" compound CaCu2O3
Experimental and theoretical studies of the unoccupied electronic structure
of CaCu2O3 single crystals have been performed using polarization-dependent
x-ray absorption spectroscopy and band structure calculations. The measured
hole distribution shows an unusual large number of holes in orbitals parallel
to the interlayer direction which is in agreement with the theoretical
analysis. CaCu2O3 deviates significantly from the standard pd-sigma cuprate
picture. The corresponding strong interlayer exchange is responsible for the
missing spin gap generic for other two-leg ladder cuprates.Comment: 4 pages, 3 figures include