Chiral flat band superconductivity from symmetry-protected three-band crossings

TL;DR

This paper demonstrates that symmetry-protected three-band crossings can host chiral flat band superconductivity, leading to enhanced critical temperatures and the emergence of Majorana fermions both in the bulk and on the surface.

Contribution

It introduces a novel mechanism for flat band superconductivity at three-band crossings with symmetry protection, revealing new Majorana fermion states.

Findings

Flat band pairing dramatically enhances superconductivity with linear Tc scaling.

Chiral p±ip flat band superconductivity appears in multicomponent channels.

Majorana fermions emerge at bulk nodal points and on the surface as arcs.

Abstract

We show that chiral (nearly) flat band superconductivity can develop and host novel Majorana fermions at a time-reversal pair of symmetry-protected three-band crossing points. Based on symmetry analysis, mean-field study, and superfluid stiffness calculation, we determine and analyze the irreducible pairing channels with flat band pairings in the low-energy spin-$1$ fermion theory. Flat band pairing can enhance superconductivity dramatically, where the critical temperature scales linearly in the interaction strength. While fully gapped flat band pairing states develop in the single-component pairing channels, we find chiral $\bar p\pm i\bar p$ flat band superconductivity in the multicomponent pairing channels. Three-dimensional itinerant Majorana fermions arise at the bulk nodal points, whereas Majorana arcs appear on the surface.