Münster 1999 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 9: Postersitzung I: TT-Teilchendetektoren (1-7), TT-Techniken (8-11), 2-D-Systeme (12-21), Meso- u. nanoskopische Strukturen (22-44), Niederdim. Spinsysteme (45-60), Tunneln u. Symmetrien (61-65), SQUID-Anwendungen (66-73), Massive HTSL, Bandleiter (74-96)

TT 9.52: Poster

Dienstag, 23. März 1999, 09:30–12:30, Z

Investigation of ladder and chain related spin gaps by inelastic light scattering in (Sr,Ca)₁₄Cu₂₄O₄₁ — •M. Grove¹, P. Lemmens¹, G. Güntherodt¹, U. Ammerahl², B. Büchner², R. Gross², G. Dhalenne³, A. Revcolevschi³, M. Uehara⁴, and J. Akimitsu⁴ — ¹2. Physikalisches Institut, RWTH Aachen, 52056 Aachen — ²2. Physikalisches Institut, Universität zu Köln, 50937 Köln — ³Universität Paris-Süd, 91405, Orsay, Frankreich — ⁴Aoyama Gakuin University, Tokyo, Japan

Raman scattering studies on single crystals of Sr_14−xCa_xCu₂₄O₄₁ (x=0, 2, 5, 12), which contain simple edge sharing CuO₂ chains and two-leg Cu₂O₃ ladders are reported. Numerous experiments showed gaps in the spin excitation of both chains and ladders. An important question is how these gaps are influenced by Ca substitution. Recent NMR studies [1] observed a reduction of the spin gap in the ladder from 550 K to 270 K.

Raman spectra on stoichiometric Sr₁₄Cu₂₄O₄₁ with polarization parallel to the ladder and chain direction (cc) show a gap of the chain Δ_chain=140±10 K as drop of scattering intensity and of the ladder Δ_ladder=350±20 K as an additional shoulder. In contradiction to Ref. 1 we observe no change concerning the energy of spin gap in the ladder but a smoothing of the observed shoulder with Ca substitution. However the gap in the chains is no longer observable. Work supported by DFG through SFB 341, BMBF Fkz. 13N7329 and INTAS 96-410

[1] K. Magishi et al., Phys. Rev. B 57, 11533 (1998)