PerspectiveCONDENSED MATTER PHYSICS

Catching structural transitions in liquids

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Science  14 Jun 2019:
Vol. 364, Issue 6445, pp. 1032-1033
DOI: 10.1126/science.aax6333

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Summary

Phase-change random-access memory is a key ingredient for nonvolatile memory and neuro-inspired computing devices (1, 2). It exploits the ability of chalcogenide phase-change materials (PCMs) to rapidly switch between logic states “0” (glassy) and “1” (crystalline). The “0” state is reached through fast quenching of the melted PCM (cooling at a rate that retains the amorphous atomic arrangement in the liquiid). In this process, the diffusivity and viscosity change by ∼17 orders of magnitude, the majority of which happens over a narrow temperature range (1). What is happening inside the cooling liquid to make this possible has remained elusive because characterization that requires nanoseconds of measurement time is intercepted by crystallization. On page 1062 of this issue, Zalden et al. (3) overcame this challenge by using femtosecond pulse x-ray diffraction and captured a liquid-liquid transition (LLT) in PCM liquids during superfast cooling.

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