Regensburg 2002 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 22: Postersitzung III: Syst. korr. Elektr.: Theorie II (1-15), Metall-Isol.- und Phasenüberg
änge (16-33), SL: Massivmat., Bandl., Pinning, Vortexdyn., Transport, Korngr. (34-43), Niedrigdim. Syst., Magnetotransport (44-63)

TT 22.63: Poster

Donnerstag, 14. März 2002, 14:00–17:30, A

Interplay of magnetic excitations and of charge dynamics in the two-leg spin 1/2 ladders of (Sr,Ca,La)14Cu24O41 — •M. Windt1, M. Grüninger1, J. Puchalla1, A. Freimuth1, C. Knetter2, K.P. Schmidt2, G.S. Uhrig2, T. Nunner3, T. Kopp3, U. Ammerahl1,4, B. Büchner5, and A. Revcolevschi41II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln — 2Institut für Theoretische Physik, Universität zu Köln — 3Experimentalphysik VI, Universität Augsburg — 4Laboratoire de Chimie des Solides, Université Paris-Sud, France — 5II. Physikalisches Institut, RWTH-Aachen

Phonon-assisted two-triplet absorption in spin-1/2 two-leg ladders is studied both experimentally and theoretically. We present optical conductivity data of (Sr,Ca,La)14Cu24O41 between 4 K and 500 K for Ec (legs) and Ea (rungs). In the undoped ladder we observe two-triplet bound states with Stot=0 below the continuum absorption [1,2,3]. Three different theoretical approaches (Jordan-Wigner fermions, perturbation theory and DMRG) describe the data very well for J ≈ 1020 − 1100 cm−1 and J/J ≈ 1 − 1.2. Consistency with the observed spin gap is obtained by taking into account a finite ring exchange [4]. With increasing temperature a dramatic increase of continuum absorption is observed. The effect of hole doping and of charge order on the magnetic excitations of the ladder is studied both experimentally and theoretically.

[1] M. Windt et al., Phys. Rev. Lett. 87, 127002 (2001).

[2] C. Knetter et al., Phys. Rev. Lett. 87, 167204 (2001).

[3] M. Grüninger et al., cond-mat/0109524.

[4] T. Nunner, P. Brune, T. Kopp, preprint, see this conference.

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