Does tetragonal FeSe1-xSx host Bogoliubov Fermi surfaces
In plain words
Beyond the nematic critical point, $\mathrm{FeSe}1-x\mathrm{S}x$ keeps many zero-energy excitations inside its superconducting state, which may signal surfaces of zero-energy quasiparticles (Bogoliubov Fermi surfaces) or simply disorder.
Precise statement
For tetragonal FeSe1-xSx with $x > 0.17$, determine whether the large residual zero-energy density of states measured by specific heat, thermal conductivity and tunneling comes from Bogoliubov Fermi surfaces of a time-reversal-breaking or interband-pairing state, or from pair breaking by disorder. An answer is a measurement of the dependence of the residual density of states on controlled disorder and field, compared with both scenarios.
What would settle it
Electron-irradiation series and muSR or Kerr tests for time-reversal breaking on the same crystals, together with field-dependent tunneling.