An elusive "demon" particle has been observed inside a superconductor nearly 70 years after it was first predicted. Its discovery could help resolve the mystery of how superconductors work.
Pines' demon is a transparent, chargeless particle discovered inside a sample of the superconductor strontium ruthenate. It is a plasmon — a ripple across the electrons of a plasma that behaves much like a particle — meaning it's a quasiparticle.
