Phase stiffness in flat-band superconductors with nodal pairing

Abstract

We study Bogoliubov quasiparticle spectrum in a two-band system with momentum-dependent hybridization between a dispersive band and a flat band. The interplay between the interband mixing and intraband Cooper pairing may give rise to a parabolic node in the spectrum of flat band quasiparticles, resulting in a quadratic temperature dependence of the superconducting phase stiffness at low temperatures. We also comment that nonmagnetic disorder induces Machida-Shibata deep subgap resonances suggesting the sensitivity of flat-band superconductivity to disorder.

Figures (2)

• Figure 1: Plot of the band dispersion $\epsilon_{{\bm k}}$ in Eq. (\ref{['Normal_disp']}), normalized by $\eta$ for different values of the parameter $2 m v^2/\eta = 0, 0.1, 0.9$. As this parameter increases, the lower band flattens.
• Figure 2: Plot of the lower band dispersion in Eq. (\ref{['Dispersion_SC']}), $E_{{\bm k},-}$, normalized by $\eta$ as a function of $\lambda k$ for different values of the parameters: dashed curves correspond to the $\pi$-shift case $\Delta_1 = -\Delta_2=0.3 \eta$; the curves that vanish at the origin correspond to $\Delta_1=0, \Delta_2=0.3 \eta$; and the remaining ones to $\Delta_1=0.3 \eta, \Delta_2=0$ vanishing at large momenta as $k^{-2}$.