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Paper   IPM / Physic / 6854
School of Physics
  Title:   Coherent Motion in the Interaction Model of Cold Glasses
  Author(s):  A. Langari
  Status:   Published
  Journal: Phys. Rev. B
  No.:  48
  Vol.:  65
  Year:  2002
  Pages:   104201-1-9
  Supported by:  IPM
We have studied the collective phenomena of multicomponent glasses at ultra low temperatures [Strehlow, et. al, Phys. Rev. Lett 80, 5361 (1998)] by taking into account the proper interaction between tunneling centers. We have considered both double and triple well potentials with different types of interactions. We show that a phase with coherent motion appears for a range of parameters when the path of tunneling is coursed by an interaction of the XY type, while the usual Ising like interaction does not lead to the expected collective phenomena. In the phase of coherent motion, the dipole moment and the low-energy levels oscillate with a frequency proportional to the number of tunneling centers in the system. Simultaneous level crossing occurs between the ground and first excited states. The effects of long-range interactions and also of random couplings have been also studied for a one- and two-dimensional array of tunneling centers. We find that long-range interactions do not affect the coherent motion, while a wide distribution of random couplings destroys the collective effects.

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