Low temperature phase separation in mixtures of ${}^3\mathrm{H}\mathrm{e}$ and ${}^4\mathrm{H}\mathrm{e}$ isotopes is a unique property of quantum fluids. Hydrogen has long been considered as another potential quantum liquid and has been predicted to be superfluid at $T\le 1\mathrm{K}$, well below freezing temperature of $\approx 14\mathrm{K}$. Phase separation has also been predicted in mixtures of para-${\mathrm{H}}_2$ and ${\mathrm{D}}_2$ at temperatures $\le 3\mathrm{K}$. To defer the freezing, we produced clusters containing para-${\mathrm{H}}_2$ and ${\mathrm{D}}_2$ at an estimated temperature of $\approx 2\mathrm{K}$ whose state was studied by vibrational Raman spectroscopy. The results indicate that the clusters are liquid and show the phase separation of the isotopes. The phase separation is further corroborated by the quantum molecular dynamics simulation.

• Received 26 January 2024
• Accepted 11 April 2024

DOI:https://doi.org/10.1103/PhysRevLett.132.206001