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Abstract:
We report results for the thermal expansion, α(T), of La2CuO4 and La1.85Sr0.15CuO4. Both compounds exhibit surprisingly similar anomalies in α(T) near 36 K. While for the Sr-doped compound this anomaly is shown to indicate bulk superconductivity, for La2CuO4 it has to be attributed to a structural phase transition. Our results suggest that the onset of superconductivity, both in minor parts of the volume in La2CuO4 and in the bulk of La1.85Sr0.15CuO4, is accompanied and possibly even triggered by this structural transition.