We present experimental evidence for a dramatic suppression of the phononic thermal conductivity of rare earth and Sr doped La 2 CuO 4 . Remarkably, this suppression correlates with the occurrence of superconductivity. Conventional models for the phonon heat transport fail to explain these results. In contrast, a straightforward explanation is possible in terms of static and dynamic stripe correlations of holes and spins. PACS: 72.15.Eb Electrical and thermal conduction in crystalline metals and alloys 74.62.Dh Effects of crystal defects, doping and substitution 74.72.Dn La-based cuprates Typeset using REVT E X

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