  The Chandrasekhar-Clogston limit normally places stringent conditions on the
magnitude of the magnetic field that can coexist with spin-singlet
superconductivity, restricting the critical induced Zeeman shift to a fraction
of the superconducting gap. Here, we consider a model system where the
spin-singlet Cooper pairing in a dispersive band crossing the Fermi level is
boosted by an additional flat-band located away from the Fermi level. The
boosting of the pairing in the dispersive band allows for nontrivial solutions
to the coupled gap equations for spin-splitting fields considerably larger than
the superconducting gaps at zero field. Further, the additional Cooper pairing
in the flat-band, away from the Fermi level, increases the superconducting
condensation energy without affecting the paramagnetic susceptibility of the
system, making the free energy favor the superconducting state. This opens up
the possibility for spin-singlet superconductivity beyond the standard
Chandrasekhar-Clogston limit.
