Fig. 2

Controlled cooling of spin ice below its freezing temperature. How the temperature of the samples varies during and after the AQP: a The applied field (black) during an AQP, and the temperatures measured by a small thermometer glued directly on top of the samples (schematically shown in (b)) vs. log time for Ho₂Ti₂O₇ (HTO, red) and ^natDy₂Ti₂O₇ (DTO, blue). The inset shows a zoom of the first 6 s vs. time. b Comparison of the sample cooling rates dT/dt as a function of temperature after the AQP for Ho₂Ti₂O₇ and ^natDy₂Ti₂O₇ from the data in (a) to the equilibrium cooling rate dT/dτ extracted from ac susceptibility data for the two samples (see Supplementary Fig. 6). The cooling rate for Ho₂Ti₂O₇ crosses the equilibrium rate at ~0.9 K, and ^natDy₂Ti₂O₇ at 0.72 K