Kavli Affiliate: J. C. Seamus Davis
| First 5 Authors: Jahnatta Dasini, Jahnatta Dasini, , ,
| 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 $T approx 750$ mK and
then collapses along with coincident loss of ergodicity below $T lesssim 500$
mK. Moreover, the four-point dynamical susceptibility $chi_4(T, t)$ is
determined directly from temperature dependence of correlations in $M(t,T)$, it
evolves as predicted when dynamical heterogeneity is present, clearly revealing
its simultaneously diverging length and time scales, $xi(T)$. and $tau_4(T)$.
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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