Modulated‐bath calorimetry

A new high‐resolution ac calorimetric technique is described for measuring the absolute heat capacity of extremely small samples. The method uses a thermocouple as the weak link to the bath and modulates the temperature of the bath sinusoidally in time. This eliminates the need for a separate thermometer and heater on the sample while retaining the ability to make absolute measurements with minimal addenda. Results for a 2.9 μg sample of the superconductor Ba0.6K0.4BiO3 in a magnetic field of 60 kOe show a jump at T c =21 K, which is above the noise level of ∼2 parts in 104.