  We give a new simple derivation for the sine-Gordon description of
Berezinskii-Kosterlitz-Thouless(BKT) phase transition (is driven by vortices).
Our derivation is simpler than traditional derivations. Besides, our derivation
is a continuous field theoretic derivation by using path integration, different
from the traditional derivations which are based on lattice theory or based on
Coulomb gas model. Our new derivation rely on Abelian duality of two
dimensional quantum field theory. By utilizing this duality in path
integration, we find that the vortex configurations are naturally mapped to
exponential operators in dual description, these operators are the vortex
operators that can create vortices, the sine-Gordon description then naturally
follows. Our method may be useful for the investigation to the BKT physics of
superconductors.
