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SUMMARY:Lattice dynamics and vibrational excitations in random networks an
 d disordered crystals - Alessio Zaccone (Cavendish Laboratory\, BSS)
DTSTART:20160526T110000Z
DTEND:20160526T120000Z
UID:TALK66019@talks.cam.ac.uk
CONTACT:Salvatore Tesoro
DESCRIPTION:Random networks (e.g. actin networks) and disordered condensed
  matter (e.g. glasses) cannot be described by standard lattice dynamics co
 ncepts\, due to the lack of periodicity of the lattice. We contributed to 
 develop a formalism which extends lattice dynamics to aperiodic solids\, i
 ncluding glasses (e.g. metallic glasses)\, by building on the key concept 
 of nonaffine displacements. Atoms in a perfect centro-symmetric crystals a
 re local centers of inversion symmetry. In disordered and defective lattic
 es\, this is no longer true. This simple symmetry consideration has huge i
 mplications for the dynamics: under an applied deformation field\, forces 
 received by a test atom from its neighbours cannot cancel by symmetry in t
 he displaced position prescribed by the deformation tensor. Hence\, the at
 omic displacement cannot be a simple affine transformation\, but necessari
 ly implies extra displacements necessary to keep mechanical equilibrium wh
 ich are called non-affine displacements [1]. Implementing this basic fact 
 in lattice dynamics leads to a number of predictions which can explain var
 ious anomalous features in: the elastic constants [2]\, the glass-liquid t
 ransition [3]\, the vibrational density of states and low-T specific heat 
 of glasses [4]\, the non-linear deformation and yielding of glasses [5].\n
 \n[1] A. Zaccone & E. Scossa-Romano\, Phys. Rev. B 83\, 184205 (2011). [2]
  A. Zaccone & E.M. Terentjev\, J. Appl. Phys. 115\, 033510 (2014). [3] A. 
 Zaccone & E. Terentjev\, Phys. Rev. Lett. 110\, 178002 (2013). [4] R. Milk
 us & A. Zaccone\, Phys. Rev. B 93\, 094204 (2016). [5] A. Zaccone\, P. Sch
 all\, E. M. Terentjev\, Phys. Rev. B 90\, 140203(R) (2014).
LOCATION:TCM Seminar room\, 530 Mott building
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