Bose–Einstein condensation of quasiparticles in graphene

Abstract

The collective properties of different quasiparticles in various graphene based structures in high magnetic field have been studied. We predict Bose-Einstein condensation (BEC) and superfluidity of 2D spatially indirect magnetoexcitons in two-layer graphene. The superfluid density and the temperature of the Kosterlitz-Thouless phase transition are shown to be increasing functions of the excitonic density but decreasing functions of magnetic field and the interlayer separation. The instability of the ground state of the interacting 2D indirect magnetoexcitons in a slab of superlattice with alternating electron and hole graphene layers (GLs) is established. The stable system of indirect 2D magnetobiexcitons, consisting of pair of indirect excitons with opposite dipole moments, is considered in graphene superlattice. The superfluid density and the temperature of the KosterlitzThouless phase transition for magnetobiexcitons in graphene superlattice are obtained. Besides, the BEC of excitonic polaritons in GL embedded in a semiconductor microcavity in high magnetic field is predicted. While superfluid phase in this magnetoexciton polariton system is absent due to vanishing of magnetoexciton-magnetoexciton interaction in a single layer in the limit of high magnetic field, the critical temperature of BEC formation is calculated. The essential property of magnetoexcitonic systems based on graphene (in contrast, e.g., to a quantum well) is stronger influence of magnetic field and weaker influence of disorder. Observation of the BEC and superfluidity of 2D quasiparticles in graphene in high magnetic field would be interesting confirmation of the phenomena we have described.

Finite-temperature pseudospin torque effect in graphene bilayers

“…The gate voltages are set to be V tg = -V bg = 400 mV which corresponds to an electron and hole density of n e = n h = 1 × 10 13 cm −2 which places the system firmly in the dense electron-hole regime where we expect the electron-hole pairs to form a BCS like state. This is as opposed to the dilute limit of electron-hole densities which can be described as a weakly interacting Bose system of excitons 13 . We choose a single particle tunneling amplitude of ∆ sas = 100 µeV.…”

The effect of disorder in superfluid double layer graphene

“…Here, we focus on the regime where the layer electron and hole populations place the system firmly in the dense electron-hole regime where we expect the electron-hole pairs to form a BCS-type state. This is as opposed to the dilute limit of electronhole densities which can be described as a weakly inter-acting Bose system of excitons 47 . As we wish to collect a sufficient statistical distribution on the effects of vacancy distribution on the interlayer transport properties of double layer graphene, we utilize several randomized vacancy configurations for each concentration we examine in this work.…”

Spin and valley degrees of freedom in a bilayer graphene quantum point contact: Zeeman splitting and interaction effects

“…These effects are expected to be particularly important in very clean samples, at very low densities, and in high magnetic fields. Proposed theories include superconducting instabilities [17][18][19][20], (anti-)ferromagnetic instabilities [21][22][23], excitonic instabilities [24][25][26], and whole lot of others [27][28][29][30][31][32][33]. For a summary or comparison see, e.g., Refs.…”