Dresden 2003 – scientific programme
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TT: Tiefe Temperaturen
TT 6: Postersitzung I (Amorphe- u. Tunnelsysteme, Niedrigdimensionale Systeme, Supraleitung: Elektronenstruktur, Phononen, Tunneln, Ordnungsparameter)
TT 6.28: Poster
Monday, March 24, 2003, 14:30–19:00, P2c, P2d
Magnetic excitations in low-dimensional quantum spin systems: an infrared study — •M. Windt1, M. Grüninger1, J. Puchalla1, E. Benckiser1, C. Hilgers1, A. Freimuth1, C. Knetter2, K.P. Schmidt2, G.S. Uhrig2, T. Nunner3, T. Kopp3, U. Ammerahl1,4, B. Büchner5, A. Revcolevschi4, C. Sekar6, G. Krabbes6, A. Löffert7, C. Gross7, and W. Assmus7 — 1II. Phys. Inst., Uni. Köln — 2Inst. für Theo. Physik, Uni. Köln — 3EP VI, Uni. Augsburg — 4Lab. de Chimie des Solides, Uni. Paris-Sud, France — 5II. Phys. Inst., RWTH-Aachen — 6IFW Dresden — 7Phys. Inst. Uni. Frankfurt
Recently, we reported the first observation of a two-triplet bound state in a two-leg S=1/2 ladder [1]. This was achieved by measuring the phonon-assisted two-triplet absorption in (La,Ca)14Cu24O41. The optical conductivity σ(ω) agrees very well with the results of three different theoretical approaches (Jordan-Wigner fermions, continuous unitary transformations and DMRG). We find J∥/J⊥ ≈ 1.3, Jcyc / J⊥≈ 0.2 and J⊥≈ 1000 cm−1, which demonstrates that the cyclic exchange is sizable [2]. With increasing temperature a dramatic change of the line shape of σ(ω) is observed. The effects of hole doping and charge order are studied by comparison with Sr14Cu24O41, Sr11Ca3Cu24O41, and La1Sr13Cu24O41. We discuss a modulation of the exchange parameters [3] and the relationship between the S=1/2 ladder and an S=1 chain. Finally, we present results for CaCu2O3 and SrCu2O3.
[1] M. Windt et al., Phys. Rev. Lett. 87, 127002 (2001).
[2] T. Nunner et al., Phys. Rev. B 66, 180404(R) (2002).
[3] K. Schmidt et al., cond-mat/0210092.