Strongly Correlated Fermionic Systems

In strongly correlated fermionic systems, the electron-electron Coulomb repulsion is important enough to interfere with transport properties. Amongst the amazing properties of these systems we find high temperature unconventional superconductivity in cuprates and pnictides; collosal magnetoresistance in manganites; quantum phase transitions; and non Fermi liquid behavior.


The discovery of superconductivity in cuprates was a huge milestone in condensed matter physics. Almost 180 000 papers and 30 years later, the problem is still open and challenging. Over the years we have looked at several aspects of cuprates. A few of them:

  • What is the superconducting glue?
  • What is the superfluid stiffness and how does it relate to fundamental excitations?
  • How can we track gaps using the f-Sum Rule?
  • Are electron-doped cuprates the same as hole-doped?
  • What information can we get from the "optical phase diagram"?



As time went by, the unsolved cuprates physics led to the decline in the interest on superconductivity. Little did we know that pnictides were just around the corner. These iron-arsenide based supercondutors, in many aspects, bridge the gap between conventional superconductors and cuprates. In other aspects there are an uncharted territory. Some questions we tackle with optical conductivity are:

  • Can we detected any optical signature of a possible s± gap symmetry?
  • How does doping in the various sites of BaFe2Fe2 affect superconductivity?
  • What are the multiband signatures in the optical conductivity?
  • Do magnetic order and superconductivity compete or cooperate?



The hidden order in URu2Si2 has been a long standing puzzle in condensed matter. Naturaly, with optical conductivity we looked at properties of this hidden order state. But we also found interesting properties on the normal state.


Proceed to "Cuprates"