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

The experimental search for the liquid-liquid critical point in water is challenging due to rapid ice crystallization. We studied supercooled water at time scales prior to ice formation by isochoric heating of 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 spanning the region of the predicted critical point. Our results revealed 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 consistent with a critical divergence at 210±10 K coincident with enhanced density fluctuations.  These results suggest that our experiments have directly probed states in the vicinity of a critical point in supercooled water., , , # Experimental evidence of a liquid-liquid critical point in supercooled water

Dataset DOI: [10.5061/dryad.pc866t23j](https://doi.org/10.5061/dryad.pc866t23j)

## Description of the data and file structure

Pump-probe measurements using infrared and x-ray laser beams were performed on high-density amorphous (HDA) ice and low-density amorphous (LDA) ice samples. The samples were isochorically heated by the IR laser and then decompressed. The X-ray scattering patterns were measured along the decompression process. 

### Files and variables

#### File: main_figure_data_fig2.xlsx

**Description:** X-ray scattering during the decompression process of HDA at different laser fluences. Wide angle x-ray scattering (WAXS) intensities around the first peak and small angle x-ray scattering (SAXS) intensities at different delays after laser pumping.  

(A) 3 J/cm^2^ WAXS (B) 3 J/cm^2^ SAXS

(C) 11 J/cm^2^ WAXS (D) 11 J/cm^2^ SAXS

(E) 15 J/cm^2^ WAXS (F) 15 J/cm^2^ SAXS

(G) 20 J/cm^2^ WAXS (H) 20 ...