We study the effect of electron-electron interactions in the quasiparticle dispersion of a graphene bilayer within the Hartree-Fock-Thomas-Fermi theory by using a four-bands model. We find that the electronic fluid can be described by a non-interacting like dispersion but with renormalized parameters. We compare our results with recent cyclotron resonance experiments in this system. Since graph...

Functional quantum theory of free Fermi fields is treated for the special case of a free Dirac field. All other cases run on the same pattern. Starting with the Schwinger functionals of the free Dirac field, functional equations and corresponding many particle functionals can be derived. To establish a functional quantum theory, a physical interpretation of the functionals is required. It is pr...

A magnetoconductivity formula is presented for the surface states of a magnetically doped topological insulator. It reveals a competing effect of weak localization and weak antilocalization in quantum transport when an energy gap is opened at the Dirac point by magnetic doping. It is found that, while random magnetic scattering always drives the system from the symplectic to the unitary class, ...

Two-dimensional (2D) materials are well-known to exhibit interesting phenomena due to quantum confinement. Here, we show that quantum confinement, together with structural anisotropy, result in an electric-field-tunable Dirac cone in 2D black phosphorus. Using density functional theory calculations, we find that an electric field, E ext, applied normal to a 2D black phosphorus thin film, can re...

We investigate the magnetotransport properties of strained 80 nm thick HgTe layers featuring a high mobility of μ ∼ 4 × 10(5) cm(2)/V · s. By means of a top gate, the Fermi energy is tuned from the valence band through the Dirac-type surface states into the conduction band. Magnetotransport measurements allow us to disentangle the different contributions of conduction band electrons, holes, and...

Electronic instabilities at the crossing of the Fermi energy with a Van Hove singularity1 in the density of states often lead to new phases of matter such as superconductivity2,3, magnetism4 or density waves5. However, in most materials this condition is difficult to control. In the case of single-layer graphene, the singularity is too far from the Fermi energy6 and hence difficult to reach wit...

Using polarization-resolved resonant Raman spectroscopy, we explore collective spin excitations of the chiral surface states in a three dimensional topological insulator, Bi_{2}Se_{3}. We observe a sharp peak at 150 meV in the pseudovector A_{2} symmetry channel of the Raman spectra. By comparing the data with calculations, we identify this peak as the transverse collective spin mode of surface...

We report a direct observation of surface dominated conduction in an intrinsic Bi(2)Se(3) thin film with a thickness of six quintuple layers grown on lattice-matched CdS (0001) substrates by molecular beam epitaxy. Shubnikov-de Haas oscillations from the topological surface states suggest that the Fermi level falls inside the bulk band gap and is 53 ± 5 meV above the Dirac point, which is in ag...

The optical conductivity of quasicrystals is characterized by two features not seen in ordinary metallic systems. There is an absence of the Drude peak and the interband conductivity rises linearly from a very low value up to normal metallic levels over a wide range of frequencies. The absence of a Drude peak has been attributed to a pseudogap at the Fermi surface but a detailed explanation of ...