A class of superconducting materials whose critical temperature is (relatively) high. They enable HTS magnets.
REBCO comes in the form of a flat tape. It then needs to be assembled into a cable with multiple layers of tape.
Startups like MetOx are shooting for order of magnitude improvements in the cost of making superconducting tape.
People
Zach Hartwig (see Toroidal field model coil) Makoto Takayasu Dongkeun Park