Author/Authors :
M Grüninger، نويسنده , , M Windt، نويسنده , , T Nunner، نويسنده , , C Knetter، نويسنده , , K.P Schmidt، نويسنده , , G.S Uhrig، نويسنده , , T Kopp، نويسنده , , A Freimuth، نويسنده , , Ammerahl، U. نويسنده , , B Büchner، نويسنده , , A Revcolevschi، نويسنده ,
Abstract :
Magnetic excitations in two-leg S=1/2 ladders are studied both experimentally and theoretically. Experimentally, we report on the reflectivity, the transmittance and the optical conductivity σ(ω) of undoped LaxCa14−xCu24O41 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∥/J⊥≤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.
