Peierls model and vacuum structure in N=2 supersymmetric gauge theories

We suggest the quasiparticle picture behind the integrable structure of N=2 SYM theory,which arises if the Lax operator is considered as a Hamiltonian for the fermionic system. We compare the meaning of BPS states with the one coming from the D-brane interpretation and give some evidence for the compositeness of the selfdual strings. The temperature phase transition with the disappearance of the mass gap is conjectured.