prof. dr hab. Tadeusz Kopeć (INTiBS PAN)

Teoretyczna analiza układów silnie skorelowanych fermionów za pomocą grup symetrii U(1) i SU(2)

We implement the rotationally-invariant formulation of the two-dimensional Hubbard model, with nearest neighbors hopping t, which allows for the analytic study of the system in the low-energy limit. Both U(1) and SU(2) gauge transformation are used to factorize the charge and spin contribution to the original electron operator in terms of the corresponding gauge fields. The Hubbard Coulomb energy U-term is then expressed in terms of quantum phase variables conjugate to the local charge and variable spin quantization axis, providing a useful representation of strongly correlated systems. It is shown that these gauge fields play a similar role as phonons in the BCS theory: they act as the the glue for fermion pairing.