AC-calorimetry for detecting electronic phase transitions at low temperatures using micro-chip devices

The MEMS device of TCG3880 was used for thermodynamic measurements in order to detect electronic phase transitions occur at low temperature region below 300 K under vacuum atmosphere. Using square wave currents which produce temperature modulation around the sample and the lock-in detection technique, we studied frequency dependence of the thermopile output (Vac) and observed a characteristic feature in a low-frequency region. From the temperature dependence of Vac at a fixed frequency of 3.3 Hz, we investigated a thermodynamic properties of high-Tc superconductor YBa2Cu3O7-δ and organic charge transfer salt of (DMe-DCNQI)2Li. A thermal anomaly being associated with the superconductive transition of the former compound and the broad heat capacity hump probably in relevant to the spin-Peierls transition of the latter one were observed using this micro-chip device.