Condensation of electron-hole pairs in a two-layer graphene system: Correlation effects

We estimate the strength of interaction-enhanced coherence between two graphene or topological insulator surface-state layers by solving imaginary-axis gap equations in the random phase approximation. Using a self-consistent treatment of dynamic screening of Coulomb interactions in the gapped phase, we show that the excitonic gap can reach values on the order of the Fermi energy at strong interactions. The gap is discontinuous as a function of interlayer separation and effective fine structure constant, revealing a first order phase transition between effectively incoherent and interlayer coherent phases. To achieve the regime of strong coherence the interlayer separation must be smaller than the Fermi wavelength, and the extrinsic screening of the medium embedding the Dirac layers must be negligible. In the case of a graphene double-layer we comment on the supportive role of the remote π-bands neglected in the two-band Dirac model.

show abstract

“…After completing this work we became aware of a recent study which reaches similar conclusions to the ones we have presented 34 .…”

Section: Summary and Discussionsupporting

confidence: 72%

Interaction-enhanced coherence between two-dimensional Dirac layers

2012

View full text Add to dashboard Cite

show abstract

“…(Here k ðeÞ F and k ðhÞ F are the Fermi wave numbers in the layers with n-and p-doping, respectively.) Indeed, such a mismatch is expected 61 to weaken the robustness of the exciton-condensate phase in which the condensed e-h pairs have zero total momentum ' K. However, preliminary calculations including screening in the condensed phase [62][63][64] ARTICLE persists even in the presence of these values of Dk F , with T c scales comparable to those reported here. On the other hand, a mismatch in the Fermi wave numbers of the two fluids may favour Fulde-Ferrell-Larkin-Ovchinnikov 65 or Sarma 66 phases.…”

Section: Discussionsupporting

confidence: 60%

Anomalous low-temperature Coulomb drag in graphene-GaAs heterostructures

et al. 2014

View full text Add to dashboard Cite

Vertical heterostructures combining different layered materials offer novel opportunities for applications and fundamental studies. Here we report a new class of heterostructures comprising a single-layer (or bilayer) graphene in close proximity to a quantum well created in GaAs and supporting a high-mobility two-dimensional electron gas. In our devices, graphene is naturally hole-doped, thereby allowing for the investigation of electron-hole interactions. We focus on the Coulomb drag transport measurements, which are sensitive to many-body effects, and find that the Coulomb drag resistivity significantly increases for temperatures o5-10 K. The low-temperature data follow a logarithmic law, therefore displaying a notable departure from the ordinary quadratic temperature dependence expected in a weakly correlated Fermi-liquid. This anomalous behaviour is consistent with the onset of strong interlayer correlations. Our heterostructures represent a new platform for the creation of coherent circuits and topologically protected quantum bits.

show abstract

“…15. It was shown 15 that the second-order vertex corrections amount only to about 5% of the first-order coupling constants and thus can be neglected. The general argument for neglecting the vertex corrections in the graphene system is that they are small by the factor 1/N , where N is number of electron flavors (N = 4 corresponds to four spin-valley components).…”

Section: Suppression Of Screening Caused By the Electron-hole Pairingmentioning

confidence: 99%

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

Germash

Fil

2015

Phys. Rev. B

View full text Add to dashboard Cite

We study how the electron-hole pairing reveals itself in the response of a double layer graphene system to the vector and scalar potentials. Electron-hole pairing results in a rigid (London) relation between the current and the difference of vector potentials in two adjacent layers. The diamagnetic effect can be observed in multiple connected systems in the magnetic field parallel to the graphene layers. Such an effect would be considered as a hallmark of the electron-hole pairing, but the value of the effect is extremely small. Electron-hole pairing significantly changes the response to the scalar potential, as well. It results in a complete (at zero temperature) or partial (at finite temperature) suppression of screening of the electric field of a test charge situated at some distance to the double layer system. A strong increase of the electric field induced by the test charge under decrease in temperature can be considered as a spectacular hallmark of the electron-hole pairing.

show abstract

Condensation of electron-hole pairs in a two-layer graphene system: Correlation effects

Cited by 89 publications

References 55 publications

Interaction-enhanced coherence between two-dimensional Dirac layers

Interaction-enhanced coherence between two-dimensional Dirac layers

Anomalous low-temperature Coulomb drag in graphene-GaAs heterostructures

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

Contact Info

Product

Resources

About