| Melting is intimately related to the elastic properties of the crystal because of the proliferation of topological defects. This is most clearly borne out in the two step melting scenario by Kosterlitz, Thouless, Halperin, Nelson and Young for 2D melting by unbinding of dislocation pairs into free dislocations followed by their unbinding into free disclinations. Video-microscopy experiments on superparamagnetic colloidal particles confined to the air/water interface reveal clear evidence for all features of the KTHNY melting scenario; in particular, the Young\x{2019}s modulus and Frank elastic constant as obtained from particle position fluctuations approach universal values of 16pi and 72/pi, respectively, at the crystal-to-hexatic and hexatic-to-liquid transition. A similar analysis of 3D crystals of charged colloids reveal that the Cauchy-relations are not fulfilled providing evidence for non-central many particle interactions. |
|