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Magnetic excitations in two-leg spin 1/2 ladders: experiment and theory

M. Grueninger·M. Windt·T. Nunner·C. Knetter·K. P. Schmidt·G. S. Uhrig·T. Kopp·A. Freimuth·U. Ammerahl·B. Buechner·A. Revcolevschi
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Abstract

Magnetic excitations in two-leg S=1/2 ladders are studied both experimentally and theoretically. Experimentally, we report on the reflectivity, the transmission and the optical conductivity sigma(omega) of undoped La_x Ca_14-x Cu_24 O_41 for x=4, 5, and 5.2. Using two different theoretical approaches (Jordan-Wigner fermions and perturbation theory), we calculate the dispersion of the elementary triplets, the optical conductivity and the momentum-resolved spectral density of two-triplet excitations for 0.2 <= J_parallel/J_perpendicular <= 1.2. We discuss phonon-assisted two-triplet absorption, the existence of two-triplet bound states, the two-triplet continuum, and the size of the exchange parameters.

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M. Grueninger, M. Windt, T. Nunner, C. Knetter, K. P. Schmidt, G. S. Uhrig, T. Kopp, A. Freimuth, U. Ammerahl, B. Buechner, A. Revcolevschi. 2001-09-27. Magnetic excitations in two-leg spin 1/2 ladders: experiment and theory. https://doi.org/10.1016/s0022-3697(02)00251-2

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