  We study the influence of quenched disorder on the two-dimensional melting
behavior by using both video-microscopy of superparamagnetic colloidal
particles and computer simulations of repulsive parallel dipoles. Quenched
disorder is provided by pinning a fraction of the particles. We confirm the
occurrence of the Kosterlitz-Thouless-Halperin-Nelson-Young scenario with an
intermediate hexatic phase. While the fluid-hexatic transition remains largely
unaffected by disorder, the hexatic-solid transition shifts towards lower
temperatures for increasing disorder resulting in a significantly broadened
stability range of the hexatic phase. In addition, we observe spatio-temporal
critical(-like) fluctuations consistent with the continuous character of the
phase transitions.
