Bogoliubov Fermi Surfaces in Spin-1/2 Systems: Model Hamiltonians and Experimental Consequences

Abstract

Bogoliubov Fermi surfaces (BFSs) are topologically protected regions of zero energy excitations in a superconductor whose dimension equals that of the underlying normal state Fermi surface. Examples of Hamiltonians exhibiting this "ultranodal" phase are known to preserve charge-conjugation ($C$) and parity ($P$) but break time-reversal ($T$). In this work, we provide examples of model Hamiltonians that do not necessarily preserve this symmetry pattern but have well-defined sign-changing Pfaffians yielding BFSs. While their topological character has not been recognized previously, some of the models we present have been extensively studied in prior literature. We further examine thermodynamic and electronic properties arising from the ultranodal state. In particular, we study the effect of a weak Zeeman field close to the topological transition and propose distinguishing features of BFSs using residual specific heat and tunneling conductance. Our calculation of the superfluid density in a toy multi-band model indicates a window of interband pairing strength where BFSs are stable with a positive superfluid density. We also present additional signatures of BFSs in spin-polarized spectral weight and total magnetization measurements.

arXiv comment13 pages, 8 figures

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• Piezoelectric effect and diode effect in anapole and monopole superconductors
• ${}^3$He Universe 2020
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• Using Disorder to Identify Bogoliubov Fermi-Surface States
• Spin fluctuations from Bogoliubov Fermi surfaces in the superconducting state of S-substituted FeSe
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• Surface density of states and tunneling spectroscopy of a spin-3/2 superconductor with Bogoliubov Fermi Surfaces
• Nonlocal thermoelectricity in quantum wires as a signature of Bogoliubov-Fermi points
• Microscopic origin of ultranodal superconducting states in spin-1/2 systems
• Impurity effect on Bogoliubov Fermi surfaces: Analysis based on iron-based superconductors
• Coexistence of Chiral Majorana Edge States and Bogoliubov Fermi Surfaces in Two-Dimensional Nonsymmorphic Dirac Semimetal/Superconductor Heterostructures
• Lifting of gap nodes by disorder in ultranodal superconductor candidate FeSe1-xSx
• Engineering subgap states in superconductors by the symmetry of altermagnetism
• Spin fluctuations in the ultranodal superconducting state of Fe(Se,S)
• Classification of multiorbital superconducting state based on augmented multipoles
• Many-body selection rule for quasiparticle pair creations in centrosymmetric superconductors
• Antichiral edge states and Bogoliubov Fermi surfaces in a two-dimensional proximity-induced superconductor
• Odd-frequency pairing of Bogoliubov quasiparticles in superconductor junction
• Thermoelectric effect in a superconductor with Bogoliubov Fermi surfaces
• Evolution and Instability of Bogoliubov Fermi Surfaces under Zeeman Field
• Quasiparticle interaction originating from Bogoliubov Fermi Surfaces under pressure in 18%-S substituted FeSe studied via NMR