In every crystal there is a set of spatial ground states, which may be occupied by electrons with opposite spins, i.e. by singlet electron pairs. If every singlet electron pair in the ground state is permanent (i.e. non-breaking), then the singlet pair is energetically more favorable than unpaired electrons. Indeed, the spin alignment of unpaired electrons randomly fluctuates (for example, due to thermal pair-breaking), forming either a temporary singlet or triplet. Thus, there is a non-zero probability that the unpaired electrons are a triplet and cannot simultaneously occupy the lowest spatial energy state. One of unpaired electrons must take a higher state, increasing the total system energy. A stable electron pair becomes possible when there is no thermal energy for the electron transfer into the higher state. Then the pairing energy is the difference between two energies: E1. Energy of the permanent singlet in the spatial ground state; E2. Energy of unpaired electrons avoiding the same spatial ground state.
The pairing energy (E1-E2) is not necessarily negligible, so below a certain temperature (say Tc) the electron pairs become stable. Can we assert that the electron pairing in superconductors is a direct consequence of the Exclusion principle? (the key word here is "direct", i.e. pairing without any mediators as phonons, excitons, plasmons, magnons etc.)