Fig. 1: Temperature dependence of the electronic specific heat of PbCuTe₂O₆.

Electronic specific heat of single crystal sc #5(b) (black squares) and a pressed-powder sample pd #Ι(b) (orange spheres). Thin solid lines serve as guides to the eyes. Very similar results to those on sc #5(b) were obtained on a second single crystal #1(b) studied in this experiment, which was grown using a different technique, see “Methods” and Supplementary Fig. 2. For the nuclear contributions subtracted, see “Methods” and Supplementary Fig. 2 and Note 2. Error bars represent the standard deviation due to statistical treatment of raw data. The inset shows the entropy in units of Rln2 for both samples using the same color code. The arrow marks the position of the phase transition anomaly in C_e(T). The entropy release associated with the phase transition over a narrow temperature window of about 0.2 K amounts to a few percent of Rln2.