Cuprates

Cuprates:  

The so-called “pseudogap quantum critical point” where the carrier density jumps from x (the doping density) to 1+x is a focal point in this workshop. The reason this phenomenon is put under the spot light is because in the absence of translation symmetry breaking, carrier density x violates the Luttinger theorem hence implies unconventional state of matter. In this workshop we have researchers who did the experiments for both electron and hole doped cuprates giving summary of their results. Interestingly the carrier density “jump” was observed for both, but for electron-doped cuprates there is a significant indication that such jump is due to the vanishing of the antiferromagnetic long range order (hence the x à 1+x transition can be attributed to the Fermis surface reconstruction). For the hole doped cuprates it is still up in the air whether analogous symmetry breaking exists. For example the ARPES normal state fermi surface is segmented into “arc”, and there are theoretical proposals that this states has no symmetry breaking but carrier concentration x. Such a state if proven exists will be a major advance in condensed matter physics. However, it was also apparent from other experimental presentations that the above results, obtained in the presence of high magnetic fields, should be interpreted in the broader context of the magnetic field - temperature phase diagram, which exhibits a rich phenomenology by itself, as demonstrated in various experiments discussed at this workshop.  

Detailed ARPES experiments that might indicate the mechanism for superconductivity according to one theory, were presented and discussed in the context of other experiments that demonstrate a predicted specific broken symmetry in the pseudogap phase. 

Tentative answers were suggested to the question "Why are there so few high-temperature superconductors?" by participants experienced with the quantum chemistry of transition-metal oxides .