Dynamic symmetry breaking in a model of polymer reptation

A numerical study of the transition between oriented and nonoriented polymers in a model for reptation is presented. An electric field biases a charged polymer to drift in the direction of its leading end. At low fields this bias is not enough to orient the polymer, but at larger fields it succeeds in orienting the polymer with a definite head and tail. The resulting motion depends on the relative magnitudes of the field and the chain length. For a given chain length, the field plays the role of inverse temperature in this transition. The critical field between these ''phases'' is found to be a non-trivial power of the length of the chain. This scaling extends over two full decades in the coupling parameter and the simulations performed involved 2 X 10(9) Monte Carlo steps per data point.