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 9.51: Poster

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

Spin gap behavior and charge ordering in α′-NaV₂O₅ and α′-Na_1−xLi_xV₂O₅ probed by light scattering — •M. Fischer¹, E. Sherman¹, P. Lemmens¹, G. Güntherodt¹, E. Morré², C. Geibel², and F. Steglich² — ¹2. Physikalisches Institut, RWTH Aachen, Templergraben 55, 52056 Aachen — ²Max-Planck Institut für chemische Physik fester Stoffe, 01187 Dresden

The quarter-filled ladder system α^′-NaV₂O₅ undergoes a phase transition into a singlet ground state at T_SP= 34 K. Raman scattering studies on single crystalline samples of α^′-Na_1−xLi_xV₂O₅ were performed in a wide substitution (x=0-7 %) and temperature range (T=5-300 K) in order to understand the interplay between the charge, spin and phonon degrees of freedom. For T≤34 K several new modes could be detected. By comparing temperature dependence of intensity, halfwidth and dependence on the sample quality three modes could be identified as magnetic bound states. Experimental evidence for a charge ordering could be detected in an anomalous shift and splitting of a V-O vibration at 422 cm⁻¹ at temperatures slightly above 34 K. The onset of this ordering is found at T_CO= 60 K and is accompanied by pretransitional fluctuations both in magnetic and phononic Raman scattering. Li substitution shifts T_SP towards lower temperatures with increasing x. The magnetic bound states and the phonon modes react in a different way on this substitution.

Work supported by DFG through SFB 341, BMBF Fkz 13N7329 and INTAS 96-410