Ultrasound evidence for multicomponent superconducting order parameter in Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ with electron quadrupling phase

Chris Halcrow, Ilya Shipulin, Federico Caglieris +6

Experiments have pointed to the formation of the electron quadrupling condensate in Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ at $x\sim 0.8$. The state spontaneously breaks time-reversal symmet…