X-ray diffraction from supercooled liquid hydrogen and deuterium mixtures *

The nucleation and growth of metastable structures in supercooled liquids is a mostly unexplored phenomenon in condensed matter physics. Moreover, the study of supercooled isotopic mixtures, and the expected phase separation during crystallization, remains an experimental challenge due to the fast timescales and atomic level length scale changes. High rep-rate ultra-fast X-ray diffraction with high peak brightness in combination with a liquid microjet is an effective method to dynamically probe the crystallization processes experimentally [1-4]. These cryogenic jet targets are created by liquefying an ultra-high purity gas in a copper assembly cooled down to cryogenic temperatures. The liquid is continuously injected into a vacuum chamber through a micron-sized aperture, where it rapidly solidifies via evaporative cooling [3]. Since cryogenic jets are not limited to a single sample gas it presents an ideal target for studying crystallization processes of isotopic, or binary, liquid mixtures with microscopic precision. Here, we report the first comprehensive time resolved observations of liquid hydrogen and deuterium mixtures, supercooled to temperatures below the melting point using X-ray diffraction from the Linac Coherent Light Source (LCLS).

 

1. 1. J. B. Kim, S. Göde, and S. H. Glenzer, Rev. Sci. Instrum., 87, 11E328 (2016)
   
   2. C. B. Curry, C. Schoenwaelder et al., J. Vis. Exp. 159, e61130 (2020).
   
   3. L. B. Fletcher et al., Rev. Sci. Inst., 87, 11E524 (2016).
   
   4. X-ray diffraction of metastable structures from supercooled liquid hydrogen, L.B. Fletcher, in Review, Phys. Rev. Materials.