Possible liquid-liquid transition of gallium confined in opal

Abstract

We have performed nuclear magnetic resonance (NMR) measurements on gallium confined in opal. In a cooling process, between 260 and $220\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the NMR spectra of gallium in opal exhibit two separate peaks at $\ensuremath{\sim}122.579\phantom{\rule{0.2em}{0ex}}48$ (low frequency, LF) and $\ensuremath{\sim}122.581\phantom{\rule{0.2em}{0ex}}89\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$ (high frequency, HF). These two peaks can be interpreted as the existence of two liquid gallium phases in opal. These two liquid phases of gallium have different freezing points with a transition temperature near $260\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The intensity of the LF signal decreases with the increase in intensity of the HF signals. The rapid changes of the Knight shift are at $\ensuremath{\sim}240\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for the LF signal and at $\ensuremath{\sim}183\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for the HF signal. The relaxation time ${T}_{1}$ of the NMR signals for ${\mathrm{Ga}}^{71}$ rapidly changes at $\ensuremath{\sim}240\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for the LF signal and at $\ensuremath{\sim}183\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for the HF signal, which suggests that these two kinds of liquid gallium have different freezing temperatures, $\ensuremath{\sim}240$ and $\ensuremath{\sim}183\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for the HF and LF phase, respectively.