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Abstract:
We study the influence of quenched disorder on the two-dimensional melting behavior of superparamagnetic colloidal particles, using both video microscopy and computer simulations of repulsive
parallel dipoles. Quenched disorder is introduced by pinning a fraction of the particles to an underlying
substrate. We confirm the occurrence of the Kosterlitz-Thouless-Halperin-Nelson-Young scenario and
observe an intermediate hexatic phase. While the fluid-hexatic transition remains largely unaffected by
disorder, the hexatic-solid transition shifts to lower temperatures with increasing disorder. This results in a
significantly broadened stability range of the hexatic phase. In addition, we observe spatiotemporal critical
(like) fluctuations, which are consistent with the continuous character of the phase transitions.
Characteristics of first-order transitions are not observed.
