Fig. 2: Transition into the Ultranodal state.
From: Topological ultranodal pair states in iron-based superconductors
a–d Normal state Fermi surface (red contour) and Bogoliubov Fermi surface in superconducting state (blue/green patches) for different values of the isotropic gap parameters on each pocket. Note that while results are plotted over a putative 1st Brillouin zone, the model is actually continuous. The inter-band gap component is chosen to be Δ0 = 0.4 and the time reversal broken component δ = Δ0. Anisotropic gap components are ΔΓa = 0.1, and ΔXa = ΔYa = 0.4, Isotropic gap components are given as [ΔΓ, ΔX, ΔY] in in each of the set-A: [0.40, 0.35, 0.35], B:[0.35, 0.27, 0.35], C:[0.16, 0.20, 0.25], D:[0.07, 0.07, 0.07]. Note the C2 symmetry of the nodes for larger isotropic gaps, consistent with ARPES. e Temperature dependence of the specific heat CV∕T for the sets of gap components on each pocket (A–D). f Tunneling conductance dI∕dV normalized to normal state value vs. STM bias eV, normalized to hole pocket intraband gap ΔΓA evaluated at temperature T = 0.07Tc. Curves are calculated by convolving density of states ρ(E) of 3-pocket model with Fermi function derivative25. The sets of gap values A–D span the nematic transition, with decreasing isotropic gap component Δj, between gapped/near nodal state (A) and ultranodal states (B–D). Normal state conductance (red) is also given for reference.
