Microscopic origins of ultranodal states in spin-1/2 systems

• DOI: 10.48550/arxiv.2305.15569
• Publication Date: 2023-01-01
• Authors: Yifu Cao; Chandan Setty; Laura Fanfarillo; Andreas Kreisel; P. J. Hirschfeld
• Keywords: Tetragonal crystal system; Microscopic theory

Several unconventional superconductors show indications of zero-energy excitations in the superconducting state consistent with existence a so-called Bogoliubov Fermi surface (BFS). In particular, FeSe doped S seems to acquire nonzero density states at zero energy low temperatures when into tetragonal phase, previously proposed phenomenological theory assuming an anisotropic spin singlet pairing gap coexisting nonunitary interband triplet component. Here we search for microscopic model that can support coexistence other orders, including pairing, and discuss several candidates indeed stabilize ground surfaces. We proper choice coupling strength various orders our model, spontaneous breaking $C_4$ rotational symmetry is realized temperatures, accordance recent angle-resolved photoemission experiments Fe(Se,S) phase.