Experimental evidence of a liquid-liquid critical point in supercooled water

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Abstract
The search for the liquid-liquid critical point in supercooled water is challenging owing to rapid crystallization. We studied supercooled water at timescales before ice formation by heating high- and low-density amorphous ices using infrared ultrafast laser pulses, followed by x-ray scattering. By varying the pump laser fluence, we accessed liquid states straddling the predicted critical point. We observed a crossover from a discontinuous to a continuous transition at which broad and slow structural variations occurred, consistent with critical fluctuations and slowing down. We also observed a rapid increase in the heat capacity indicating a critical divergence at 210 ± 8 K coincident with enhanced density fluctuations. These results suggest that our experiments have directly probed the vicinity of a critical point in supercooled water.
Funding Information
  • Ragnar Söderbergs stiftelse
  • Natural Sciences and Engineering Research Council of Canada (RGPIN-2024-04477)
  • Ministry of Science and ICT, South Korea (RS-2020-NR049542)
  • Ministry of Science and ICT, South Korea (RS-2024-00348773)
  • Samsung Future Technology Foundation (SSTF-BA2002-07)
  • Swedish Research Council (2013-8823)
  • Swedish Research Council (2023-5080)

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