Heat capacity of superconducting<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">La</mml:mi></mml:mrow><mml:mrow><mml:mn>1.85</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Sr</mml:mi></mml:mrow><mml:mrow><mml:mn>0.15</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">CuO</mml:mi></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

The heat capacity has been obtained for a sample of ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4}$ which is superconducting with a transition temperature ${T}_{c}$=31 K. Although the heat capacity is dominated by the lattice in the vicinity of ${T}_{c}$, it has nonetheless been possible to observe the superconducting transition, thus verifying that this is bulk superconductivity. A lower limit is established for the heat-capacity anomaly of \ensuremath{\Delta}C/${T}_{c}$=(20\ifmmode\pm\else\textpm\fi{}5) mJ/mole ${K}^{2}$. Combined with estimates of the electronic heat capacity \ensuremath{\gamma}, this leads to 2\ensuremath{\le}\ensuremath{\Delta}C/\ensuremath{\gamma}${T}_{c}$\ensuremath{\le}10, compared with the Bardeen-Cooper-Schrieffer value of 1.43, which places this material well into the strong-coupling regime.

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