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Description
The presence of multiple bands qualitatively changes the nodal structure of an inversion-symmetric time-reversal symmetry-breaking superconductor. Instead of point or line nodes, the gap exhibits extended nodal pockets, called Bogoliubov Fermi surfaces [1-4]. These surfaces originate from the “inflation” of point and line nodes in the absence of time-reversal symmetry breaking. In this work we study a paradigmatic model for Bogoliubov-Fermi surfaces, the Luttinger-Kohn Hamiltonian of spin $j=3/2$ fermions for the cubic point group, and investigate the thermodynamic stability of a time-reversal symmetry-breaking superconducting state with Bogoliubov-Fermi surfaces compared to a time-reversal symmetry-preserving one without as a function of the multiband character of the electronic band structure. We formulate a mean-field theory and minimize the free energy to find the self-consistent superconducting gap as a function of band parameters. The multiband nature gives rise to a rich phase diagram. We also study some basic spectroscopic properties and the influence of cubic anisotropy.
[1] D. F. Agterberg, P. M. R. Brydon, and C. Timm, Phys. Rev. Lett. 118, 127001 (2017)
[2] C. Timm, A. P. Schnyder, D. F. Agterberg and P. M. R. Brydon, Phys. Rev. B 96, 094526 (2017)
[3] P. M. R. Brydon, D. F. Agterberg, H. Menke, and C. Timm, Phys. Rev. B 98, 224509 (2018)
[4] H. Menke, C. Timm, Philip M. R. Brydon, Phys. Rev. B 100, 224505 (2019)
