Location of gap nodes on the Sr2RuO4 Fermi sheets
In plain words
Heat-transport data indicate lines on the Fermi surface where the superconducting gap vanishes, and tunneling maps place them along the diagonals on two of the three sheets; whether these are true zeros and what happens on the third sheet is not known.
Precise statement
In Sr2RuO4, determine whether the gap features along the zone diagonals [110] on the $\alpha$ and $\beta$ sheets are symmetry-required vertical line nodes or deep accidental minima, and determine the gap structure on the $\gamma$ sheet. An answer is momentum-resolved gap data at $T << T_c$ (ARPES with sub-0.1 meV resolution, quasiparticle interference, or field-angle-resolved specific heat) on all three sheets, resolving node versus minimum.
What would settle it
Momentum-resolved gap maps on all three sheets at temperatures well below $T_c$.
Status in the literature
Thermal conductivity (2017) indicates vertical line nodes, and quasiparticle interference (2020) places nodes or deep minima along the zone diagonals on the $\alpha$ and $\beta$ sheets; $\gamma$-sheet gap structure and true node versus minimum remain open.
Related problems
- Special case of What is the superconducting order parameter of Sr2RuO4