Evidence for hidden fermion that triggers high-temperature   superconductivity in cuprates
  In superconductors, electrons bound into Cooper pairs conduct a dissipationless current. The strength of the Cooper pairs scales with the value of the critical transition temperature (Tc). In cuprate high-Tc superconductors, however, the pairing mechanism is still unexplained. Here we unveil why in the cuprates the Cooper pairs are so strongly bound to work out the extraordinary high Tc. From one-to-one correspondence between numerical simulation on a microscopic cuprate model and a simple two-component fermion model, we show that hidden fermions emerge from the strong electron correlation and give birth to the strongly bound Cooper pairs. This mechanism is distinct from a conventional pairing mediated by some bosonic glue, such as phonons in conventional superconductors. The hidden fermions survive even above Tc and generate the strange-metal pseudogap phase. This reveals an unprecedented direct relationship between the pseudogap phase and superconductivity in the cuprates. 
Shiro Sakai, Marcello Civelli, and Masatoshi Imada
cond-mat.str-el cond-mat.supr-con