Berlin 2005 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 32: Correlated Electrons - Low-dimensional Materials II
TT 32.4: Vortrag
Dienstag, 8. März 2005, 17:00–17:15, TU H2053
Thermal conductivity of single-layered cuprates R2CuO4 — •K. Berggold1, T. Lorenz1, M. Hofmann1, J. Baier1, M. Kriener1, H. Roth1, A. Freimuth1, and S. Barilo2 — 1II. Physikalisches Institut 50937 Köln — 2Inst. of Sol. State & Semicond. Phys., Minsk
Thermal conductivity of low-dimensional spin systems is investigated because of the possibility of a large magnetic contribution to the heat transport. There is a lot of evidence for such a contribution in various 1D systems, but it is less investigated in 2D systems. We present measurements of the thermal conductivity κ of SrCuO2Cl2 [1] and R2CuO4 with R = Pr, Nd, Sm, Eu and Gd. For all samples, κ is anisotropic with a conventional low-temperature maximum for a heat current perpendicular to the Cu-O-planes, whereas for a heat current within the Cu-O-planes a second high-temperature maximum or shoulder occurs. In principle, two mechanisms could explain a double-peak structure of κ. One is an unusual phonon-damping, which is e.g. relevant in the 2D-System SrCu(BO3)2 [2]. Such a damping could arise from soft phonon modes caused by structural instabilities. The other is an additional contribution by magnetic excitations of the spin system. However, a structural instability is only present for R=Eu and Gd. Thus, the observation of a double-peak structure in all samples gives clear evidence for a sizeable heat transport by magnetic excitations. We also show, that weak charge-carrier doping strongly suppresses the magnetic contribution.
[1] M. Hofmann et al. PRB 67, 184502 (2003)
[2] M. Hofmann et al. PRL 87, 047202 (2001)
Supported by the DFG trough SFB 608