Colloquium Series

"Arrangement phases of small clusters" by Dr. Terry Sheridan, Professor of Physics, Ohio Northern University

We consider a small number n of charged particles confined in a two-dimensional biharmonic potential well. The particles interact through a screened Coulomb (i.e., Debye or Yukawa) force. In the strong-coupling regime, particle arrangements are controlled by three parameters: n, the well anisotropy, and the screening length. When the well is highly anisotropic, the arrangement is a one-dimensional straight line. As the anisotropy is reduced, or n is increased, the arrangement becomes two-dimensional via a zigzag instability. We show that the change between one and two-dimensional arrangements looks like a continuous phase transition. Additional transitions between arrangement phases, both continuous and discontinuous, are predicted. Dusty plasma experiments verify the existence of arrangement phases and give insight into the transition dynamics.

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