Interaction and coherence in 2D bilayers

Abstract

In bilayer systems, the additional layer pseudospin enables the emergence of interlayer coherence (IC), which is a direct consequence of the interlayer Coulomb interaction. This study presents a comprehensive HF investigation of IC in 2D bilayers, uncovering ground-state behaviors and temperature-dependent phase transitions that are distinct from single-layer 2DEG. This IC signals a spontaneous breaking of the U(1) symmetry in pseudospin. We explore the zero-temperature phase diagrams as a function of the electron density and interlayer separation within the HF formalism. We also calculate the critical temperature ($T_c$) of the interlayer coherence onset by self-consistently solving the HF gap-like equation. We contrast this IC phase in e-e bilayers with the closely related excitonic superfluid phase in e-h bilayers. Though both e-e and e-h bilayers spontaneously break the pseudospin U(1) symmetry, e-h bilayers produce BCS-BEC crossover intrinsic to the excitons acting as effective bosons or Cooper pairs, whereas the symmetry-broken phase in e-e bilayers is akin to the XY or easy-plane pseudospin ferromagnetism. Using the same system parameters and a similar theoretical framework, we find that $T_c$ of the interlayer coherent phase in e-e bilayers is about one-third of that in exciton condensates, suggesting a weaker IC in e-e bilayers. In addition, we examine the effect of a weak interlayer tunneling on the IC order parameter, drawing parallels with the influence of an effective in-plane magnetic field on the XY pseudospin ferromagnetism. Our findings provide a comparative theoretical framework that bridges the gap between the IC physics in e-e and e-h bilayers, contributing to a unified understanding of phase transitions in low-dimensional electron/hole systems and establishing in particular the same universality class for interlayer phase coherence in both e-e and e-h bilayers.

References in corpus (12)

• Collective excitations of a degenerate gas at the BEC-BCS crossover
• Exciton Condensation and Perfect Coulomb Drag
• Observation of pair condensation in the quasi-2D BEC-BCS crossover
• Coulomb Drag in the Exciton Regime in Electron-Hole Bilayers
• Anomalous Coulomb drag in electron-hole bilayers
• Gate-controlled BCS-BEC crossover in a two-dimensional superconductor
• Wigner supersolid of excitons in electron-hole bilayers
• Undoped Electron-Hole Bilayers in a GaAs/AlGaAs Double Quantum Well
• Trial Wavefunctions for ν= 1/2 + 1/2 Quantum Hall Bilayers
• Interlayer Transport in Bilayer Quantum Hall Systems
• Tunneling between Dilute GaAs Hole Layers
• Quantum Hall Bilayer as Pseudospin Magnet

Cited by in corpus (4)

• Eliashberg theory for dynamical screening in bilayer exciton condensation
• Pseudospin density wave instability in two-dimensional electron bilayers
• 2D bilayer electron-hole superfluidity with unequal and anisotropic masses
• Non-Fermi Liquids from Subsystem Symmetry Breaking in van der Waals Multilayers