The dependence of the specific heat of ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ on temperature $\left(T\right)$ and magnetic field $\left(H\right)$ shows a number of features predicted for $d$-wave pairing: a $T^2$ term for $H=0\mathrm{}$ and an $H^{1/2}T$ term for $H\ne 0$ and low $T$, with a crossover to a stronger $T$ dependence at higher $T$. For all $H$ and $T$, these results are consistent with a recently proposed scaling relation. Values of the parameters derived from experimental data agree with theoretical predictions.

• Received 23 March 1998

DOI:https://doi.org/10.1103/PhysRevLett.82.1550