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Cyclic Spin Exchange in Cuprate Spin Ladders

Tamara S. Nunner·Philipp Brune·Thilo Kopp·Marco Windt·Markus Grüninger
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Abstract

We investigate the influence of a cyclic spin exchange J_{cyc} on the one- and two-triplet excitations of an undoped two-leg S=1/2 ladder, using the density matrix renormalization group (DMRG). The dispersion of the S=0 two-triplet bound state is dramatically reduced by J_{cyc} due to a repulsion between triplets on neighboring rungs. In (La,Ca)_{14}Cu_{24}O_{41} a consistent description of both the spin gap and the S=0 bound state requires $J_{cyc}/J_\perp \approx 0.20-0.27$ and $J/J_{\perp} \approx 1.25-1.35$. With these coupling ratios the recently developed dynamical DMRG yields an excellent description of the entire S=0 excitation spectrum observed in the optical conductivity, including the continuum contribution.

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Tamara S. Nunner, Philipp Brune, Thilo Kopp, Marco Windt, Markus Grüninger. 2002-03-22. Cyclic Spin Exchange in Cuprate Spin Ladders. https://doi.org/10.1103/physrevb.66.180404

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