Electromagnetic response and effective gauge theory of graphene in a magnetic field

The response function of graphene is calculated in the presence of a constant current across the sample. For small drift velocities and finite chemical potential, analytic expressions are obtained and consequences on the plasmonic excitations are discussed. For general drift velocities and zero chemical potential, numerical results are presented and a plasmon gain region is identified that is related to interband transitions.

Section: Introductionmentioning

confidence: 99%

Drift-induced modifications to the dynamical polarization of graphene

Sabbaghi¹,

Lee²,

Stauber³

et al. 2015

“…The screened pseudopotential was also used (although a simplified version of it) in [14]. As in the torus geometry, the two-dimensional Coulomb potential V (q) = [25,42,43],…”

mentioning

confidence: 99%

Pfaffian state in an electron gas with small Landau level gaps

Luo

Chakraborty

2017

Landau level mixing plays an important role in the even denominator fractional quantum Hall states. In ZnO the Landau level gap is essentially an order of magnitude smaller than that in a GaAs quantum well. We introduce the screened Coulomb interaction in a single Landau level to deal with that situation. Here we study the incompressibility and the overlap of the ground state and the Pfaffian (or anti-Pfaffian) state at filling factors with a general screened Coulomb interaction. For small Landau level gaps, the overlap is strongly system size-dependent and the screening can stabilize the incompressibility of the ground state with particle-hole symmetry which suggests a newly proposed particle-hole symmetry Pfaffian ground state. When the ratio of Coulomb interaction to the Landau level gap κ varies, we find a possible topological phase transition in the range 2 < κ < 3, which was actually observed in an experiment. We then study how the width of quantum well combined with screening influences the system.The even-denominator fractional quantum Hall effect (FQHE) was observed [1,2] and studied in great detail in GaAs. It is believed that the concept of pairing of electrons is behind this unique quantum Hall state [3][4][5][6][7], though the nature of this state is still unclear. A strong candidate for the ground state is the Moore-Read Pfaffian state which contains non-abelian excitations and chiral edge modes [3,4,7]. However this topological state has not been observed directly, perhaps because the mobility of GaAs is still not high enough for this state to be detected. In other systems, such as cold atoms, the circuit and cavity QED systems [8][9][10][11], in theory it is possible to emulate this unique topological ground state by tuning the Hamiltonian to approximate the parent Hamiltonian of the Pfaffian state. The even-denominator FQHE has been studied and observed in graphene systems [12][13][14][15][16][17][18][19][20][21]. Recently, FQHE was observed again in the ZnO/MgZnO heterointerface [22][23][24]. The Pfaffian states and its topological properties can be potentially observed in this new system, albeit its low mobility. Surprisingly, in ZnO the well-known ν = 5 2 FQHE was found to go missing while its spinful electron-hole conjugate ν = 7 2 FQHE survived [24,25]. Tilted-field studies [26] also unveiled some interesting results in this system [24,27]. The ZnO system is distinctly different from the GaAs and graphene systems [16][17][18][19][20][21] since the effective mass in ZnO is very large and the Landau level (LL) gap is very small. The ratio of Coulomb interaction to the LL gap is κ = 25.1/ √ B for the magnetic field B, which is one order of magnitude higher than that in GaAs or in graphene systems. As a result, the electron-electron interaction would definitely drive the transport of the electrons unconventionally in many aspects [28]. Since the LL gaps are very small in ZnO, the Landau level mixing (LLM) is too strong to be negligible. However, it would be a major computational challenge to in...

“…The Landau levels influence the spin relaxation 25,26 , which has been measured with the help of spin coherence times 27 . The influence of magnetic fields is treated in various systems ranging from plasma 28 , solid-state plasmas 29 , and semiconductors 30 to spin-orbit coupled systems 31 and graphene 32 . The feedback of magnetization dynamics due to spins on the spin dynamics itself is reviewed in Ref.…”

Section: Introductionmentioning

confidence: 99%

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

Morawetz

2015

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.