FeSe and its relatives

Experimental facts

Can be doped with holes and electrons ( e.g. Te, Rb)
Nematic transition at 90K if undoped at ambient pressure
Superconducting down to a single layer, where Tc = 8K at ambient pressure; 30K under pressure
- electron doping can eliminate hole pocket at Gamma point; a problem for interband pairing mechanism
- If placed on top of STO, Tc rises dramatically, 80K; Presumably due to interfacial phonon with strong e-ph interaction
  - s-wave gap, 20meV https://arxiv.org/pdf/1504.02185.pdf
  - STO oxygen isotope effect observed
- review https://arxiv.org/pdf/1604.03566.pdf
magnetic order can be stripes or bistripes
"spin resonance" observed https://www.nature.com/articles/s41467-017-00162-x
AF correlations decrease and stripe increase, below nematic transition https://www.nature.com/articles/ncomms12182
strong orbital-dependent correlation effects in iron chalcogenides, ARPES https://www.nature.com/articles/ncomms8777, review https://www.nature.com/articles/s41535-017-0059-y
orbital selective SC, STM http://science.sciencemag.org/content/357/6346/75

J1, J2 model is probably insufficient
sign problem free MC is possible, http://engine.scichina.com/publisher/scp/journal/SB/61/12?slug=Browse, cooperative effect between several pairing mechanism (nematic, AF, phonons) https://doi.org/10.1007/s11434-016-1087-x
Nematic possibly driven by S = 1 quantum fluctuations, https://www.nature.com/articles/nphys3456, see also https://journals.aps.org/prb/pdf/10.1103/PhysRevB.79.174409
Electronic nematicity review, https://www.nature.com/articles/nphys2877
Orbital selective physics
- superconductivity https://arxiv.org/abs/1306.4184