Enhancement of electron-hole superfluidity in double few-layer graphene

Abstract

We propose two coupled electron-hole sheets of few-layer graphene as a new nanostructure to observe superfluidity at enhanced densities and enhanced transition temperatures. For ABC stacked few-layer graphene we show that the strongly correlated electron-hole pairing regime is readily accessible experimentally using current technologies. We find for double trilayer and quadlayer graphene sheets spatially separated by a nano-thick hexagonal boron-nitride insulating barrier, that the transition temperature for electron-hole superfluidity can approach temperatures of 40 K.

Spatially indirect exciton condensate phases in double bilayer graphene

“…A number of recent experimental papers [29][30][31][32][33] with intriguing findings demonstrate the potential for interesting many-electron physics in the double-bilayer system, a part of which is addressed here, leaving many avenues for future theoretical and experimental work.…”

“…The sensitivity of isolated bilayers to displacement fields plays an essential role in the physics we explore below. Previous theoretical work 31,32 has highlighted the potential of double bilayer graphene as a spatially indirect exciton system, but assumed simplified parabolic band dispersions for conduction and valence bands and did not explore the consequences either of this displacement-field sensitivity or of broken symmetry states in isolated bilayers. The properties of double bilayer systems can be adjusted electrically by using gates to apply a displacement field or by applying a bias voltage between bilayers, as illustrated in Fig.…”

“…Our interest however is in excitons which are present in thermal equilibrium, and this can be achieved only for spatially indirect excitons and only when two bilayer graphene systems are present and separated by an insulating barrier. [29][30][31][32][33] Spatially indirect excitons generally have smaller binding energies than spatially direct excitons because of the Schematic illustration of the experimental system modeled in this paper. An external electric field E d is applied simultaneously to two bilayers (bilayer n = 1 with layers l = 1, 2 and bilayer n = 2 with layers l = 3, 4) by external gates.…”

Diamagnetism and suppression of screening as hallmarks of electron-hole pairing in a double layer graphene system

“…The advantage of the latter system is that the coupling parameter depends on the density of carriers and this parameter can be controlled by external gates. Using few-layer ABC stacked sheets of graphene instead of monolayer or bilayer graphene sheets one may further increase the critical temperature 17 . The increasing is caused by the enhancing of the density of states in the few-layer graphene.…”

Strong enhancement of third-harmonic generation in a double layer graphene system caused by electron-hole pairing

“…The pairing was registered in double quantum well AlGaAs heterostructures in the quantum Hall state under study of their transport properties [25][26][27][28]. The possibility of electronhole pairing was also considered with reference to topological insulator heterostructures [29][30][31][32], double bilayer graphene [33], double few-layer graphene [34], transition metal dichalcogenide [35][36][37] and black phosphorene [38] double layers. Recently several experimental efforts to register electron-hole pairing in double layer graphene systems were done [39][40][41][42], but the results of these experiments are controversial.…”