Dynamical response functions and collective modes of bilayer graphene

The spin and density response functions in the random phase approximation (RPA) are derived by linearizing the kinetic equation including a magnetic field, the spin-orbit coupling, and mean fields with respect to an external electric field. Different polarization functions appear describing various precession motions showing Rabi satellites due to an effective Zeeman field. The latter turns out to consist of the mean-field magnetization, the magnetic field, and the spin-orbit vector. The collective modes for charged and neutral systems are derived and a threefold splitting of the spin waves dependent on the polarization and spin-orbit coupling is shown. The dielectric function including spin-orbit coupling, polarization and magnetic fields is presented analytically for long wave lengths and in the static limit. The dynamical screening length as well as the long-wavelength dielectric function shows an instability in charge modes, which are interpreted as spin segregation and domain formation. The spin response describes a crossover from damped oscillatory behavior to exponentially damped behavior dependent on the polarization and collision frequency. The magnetic field causes ellipsoidal trajectories of the spin response to an external electric field and the spin-orbit coupling causes a rotation of the spin axes. The spin-dephasing times are extracted and discussed in dependence on the polarization, magnetic field, spin-orbit coupling and single-particle relaxation times.

Section: Introductionsupporting

confidence: 69%

Kinetic theory of spin-polarized systems in electric and magnetic fields with spin-orbit coupling. II. RPA response functions and collective modes

Morawetz

2015

“…For neutral graphene this logarithimic velocity enhancement implies that ImΣ(ω) ∼ ω/(log ω) 2 which is smaller than ImΣ(ω) ∼ ω. In contrast to single layer graphene interactions in bilayer graphene are screened, as we have shown and has been pointed out in the literature 15,16 with Thomas-Fermi screening, that the quasiparticle dispersion in bilayer remains quadratic. Most of our analysis of quasiparticle properties in neutral bilayer graphene has relied on the fact that χ 0 ρρ (q, Ω) ∝ ω 0 (i.e.…”

supporting

confidence: 46%

Non-Fermi-liquid behavior in neutral bilayer graphene

Barlas

Yang

2009

We calculate the density-density response function and electron self-energy for undoped bilayer graphene, within the Random Phase Approximation (RPA). We show that the quasiparticle decay rate scales linearly with the quasiparticle energy, and quasiparticle weight vanishes logarithmically in the low-energy limit, indicating non-Fermi liquid behavior. This is a consequence of the absence of a Fermi surface for neutral bilayer graphene and corresponding larger phase space available for scattering processes. Experimental consequences of our results as well as their differences from those of single-layer graphene are discussed.

“…For our purpose, we assume the bilayer graphene to have parabolic chiral band structure 69,[81][82][83][84] (characterized by an effective mass m rather than a velocity v F ) in contrast to the linear chiral band structure of MLG (which is what we have considered so far in this work).…”

Section: Bilayer Graphenementioning

confidence: 99%

Intrinsic plasmons in two-dimensional Dirac materials

Sarma

2013

We consider theoretically, using the random phase approximation (RPA), low-energy intrinsic plasmons for two-dimensional (2D) systems obeying Dirac-like linear chiral dispersion with the chemical potential set precisely at the charge neutral Dirac point. The "intrinsic Dirac plasmon" energy has the characteristic √ q dispersion in the 2D wave-vector q, but vanishes as √ T in temperature for both monolayer and bilayer graphene. The intrinsic plasmon becomes overdamped for a fixed q as T → 0 since the level broadening (i.e. the decay of the plasmon into electron-hole pairs due to Landau damping) increases as 1/ √ T as temperature decreases, however, the plasmon mode remains well-defined at any fixed T (no matter how small) as q → 0. We find the intrinsic plasmon to be well-defined as long as q < k B T e 2 . We give analytical results for low and high temperatures, and numerical RPA results for arbitrary temperatures, and consider both single-layer and double-layer intrinsic Dirac plasmons. We provide extensive comparison and contrast between intrinsic and extrinsic graphene plasmons, and critically discuss the prospects for experimentally observing intrinsic Dirac point graphene plasmons.