Electron pairing with gapless excitations in mixed double layers

Abstract

We study the interlayer pairing states in layered systems of two different 2d electronic subsystems, one with relativistic linear and the other with nonrelativistic parabolic spectrum. The complex order parameter of the paired state has a two-component structure. We investigate the pairing state formation on the mean-field level, determine the critical interaction strength and evaluate the effective potential. The anisotropic three-band spectrum of quasiparticles depends explicitly on the phase difference of the order parameter components, rotates in momentum space as it changes, and exhibits the strong band deformation due to the pairing. The pairing leads to the fusion and hybridization of initially decoupled bands. The quasiparticle spectrum has the shape of deformed Dirac cones in the vicinity of the two touching points between neighboring bands. The density of states exhibits a number of specific features due to band deformation, such as a van Hove singularity.