Pairing transition in a double layer with interlayer Coulomb repulsion

Abstract

We study the effect of interlayer Coulomb interaction in an electronic double layer. Assuming that each of the layers consists of a bipartite lattice, a sufficiently strong interlayer interaction leads to an interlayer pairing of electrons with a staggered order parameter. We show that the correlated pairing state is dual to the excitonic pairing state with a uniform order parameter in an electron-hole double layer. The interlayer pairing of electrons leads to strong current-current correlations between the layers. We also analyze the interlayer conductivity and the fluctuations of the order parameter, which consists of a gapped and a gapless mode.

Electron pairing with gapless excitations in mixed double layers

“…This is very different from the case of conventional s-wave superconductivity in graphene double layers, which we investigated in Ref. [16]. In that case the spectrum has the usual shape of two paraboloids separated by the spectral gap around zero energy as shown on the right side of Fig.…”

“…Such bilayer systems may represent environments in which electron pairing between different species occurs due to Coulomb repulsion, in analogy to the case of graphene bilayer considered by us in Ref. [16]. In this paper we study such interlayer paired states.…”

“…The role of the layered structures is or might be important for understanding physical phenomena as different as the formation of interlayer exciton condensates in semiconducting devices [1][2][3][4], the interplay of excitonic superfluidity with unconventional fractional quantum Hall states in graphene bi-and double layers in external magnetic fields [5][6][7], the complex of problems with the high-T c superconductivity [8,9], the crossover between adjacent superconducting and insulating states in magic angle twisted graphene bilayers [10,11], the anomalous giant magneto-resistance and superconductivity in graphene [12][13][14] and transition metal dichalcogenide (TMDC) multilayers [15]. Recently we proposed a set of pairing states that can emerge in a layered system of two graphene layers due to repulsion between electrons from opposite layers [16]. We also pointed out a duality between electron-electron and electron-hole condensates occurring in layered graphene devices.…”

“…The justification of this approximation is given in Ref. [16] and references therein. Finally, the dot operator suggests the summation over all discrete and integration over all continuous degrees of freedom.…”

“…Right panel: 3d-plot of the quasiparticle spectrum in graphene double layers with paring discussed in Ref. [16] With variational solutions ∆ 1 = ∆ = ∆ 2 , χ 2 = χ = χ 1 and with q y = 0 the eigenvalues become:…”