Kavli Affiliate: J. C. Seamus Davis
| First 5 Authors: Jahnatta Dasini, Chaia Carroll, Chun-Chih Hsu, Hiroto Takahashi, Jack Murphy
| Summary:
Dynamical heterogeneity, in which transitory local fluctuations occur in the
conformation and dynamics of constituent particles, is widely hypothesized to
be essential to evolution of supercooled liquids into the glass state. Yet its
microscopic spatiotemporal phenomenology has remained unobservable in virtually
all molecular glass forming liquids. Because recent theoretical advances
predict that corresponding dynamical heterogeneity could occur in supercooled
magnetic monopole fluids, we searched for such phenomena in Dy2Ti2O7. By
measuring its microsecond-resolved spontaneous magnetization fluctuations
$M(t,T)$ we discovered a sharp bifurcation in monopole noise characteristics
below $T approx 1500$ mK, with the appearance of powerful spontaneous monopole
current bursts. This intense dynamics emerges upon entering the supercooled
monopole fluid regime, reaches maximum strength near $T approx 500$ mK and
then terminates along with coincident loss of ergodicity near $T lesssim 250$
mK. Moreover, the four-point dynamical susceptibility $chi_4(T, t)$ is
observed directly and evolves as predicted when dynamical heterogeneity is
present, clearly revealing its diverging length scales $xi(T)$. This overall
phenomenology greatly expands our empirical knowledge of supercooled monopole
fluids and, more generally, demonstrates direct detection of the time sequence,
magnitude, statistics and correlations of dynamical heterogeneity, access to
which may greatly accelerate fundamental vitrification studies.
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