Alev Devrim Güçlü

Magnetism and Correlations in Fractionally Filled Degenerate Shells of Graphene Quantum Dots

We show that the ground state and magnetization of the macroscopically degenerate shell of electronic states in triangular gated graphene quantum dots depends on the filling fraction of the shell. The effect of degeneracy, finite size, and electron-electron interactions are treated nonperturbatively using a combination of density functional theory, tight-binding, Hartree-Fock and configuration interaction methods. We show that electronic correlations play a crucial role in determining the nature of the ground state as a function of filling fraction of the degenerate shell at the Fermi level. We find that the half-filled charge neutral shell leads to full spin polarization but this magnetic moment can be completely destroyed by adding a single electron.

Excitonic absorption in gate-controlled graphene quantum dots

We present a theory of excitonic processes in gate controlled graphene quantum dots. The dependence of the energy gap on shape, size and edge for graphene quantum dots with up to a million atoms is predicted. Using a combination of tight-binding, Hartree-Fock and configuration interaction methods, we show that triangular graphene quantum dots with zigzag edges exhibit optical transitions simultaneously in the THz, visible and UV spectral ranges, determined by strong electron-electron and excitonic interactions. The relationship between optical properties and finite magnetic moment and charge density controlled by an external gate is predicted. Two-dimensional graphene monolayer exhibits fascinating electronic [1–6] and optical properties[7–15] due to the zero energy gap and relativistic-like nature of quasiparticle dispersion close to the Fermi level. With recent improvements in nanofabrication techniques[16] the zero energy gap of bulk graphene can be opened via engineering size, shape, character of the edge and carrier density, and this in turn offers possibilities to simultaneously control electronic[17–25], magnetic[16, 23–30] and optical[30–32] properties of a single-material nanostructure. In this paper, we present a theory and results of numerical calculations predicting the dependence of the energy gap on shape, size and edge for graphene quantum dots with up to a million atoms. We show that triangular graphene quantum dots with zigzag edges combine magnetic and optical properties tunable with carrier density, with optical transitions simultaneously in the THz, visible and UV spectral ranges. We describe one electron properties of graphene quantum dots with N atoms and

Zero-energy states in triangular and trapezoidal graphene structures

We derive analytical solutions for the zero-energy states of degenerate shell obtained as a singular eigenvalue problem found in tight-binding (TB) Hamiltonian of triangular graphene quantum dots with zigzag edges. These analytical solutions are in agreement with previous TB and density-functional theory results for small graphene triangles and extend to arbitrary size. We also generalize these solutions to trapezoidal structure which allow us to study bowtie graphene devices.

Electronic properties of gated triangular graphene quantum dots: Magnetism, correlations, and geometrical effects

We present a theory of electronic properties of gated triangular graphene quantum dots with zigzag edges as a function of size and carrier density. We focus on electronic correlations, spin, and geometrical effects using a combination of atomistic tight-binding, Hartree-Fock, and configuration interaction methods (TB + HF + CI), including long-range Coulomb interactions. The single-particle energy spectrum of triangular dots with zigzag edges exhibits a degenerate shell at the Fermi level with a degeneracy

Effect of edge reconstruction and passivation on zero-energy states and magnetism in triangular graphene quantum dots with zigzag edges

{N}_{\mathrm{edge}}

Electric-field controlled spin in bilayer triangular graphene quantum dots

proportional to the edge size. We determine the effect of the electron-electron interactions on the ground state, the total spin, and the excitation spectrum as a function of a shell filling and the degeneracy of the shell using TB + HF + CI for

Graphene Quantum Dots

{N}_{\mathrm{edge}}l12

Spin and electronic correlations in gated graphene quantum rings

and approximate CI method for

Zero-energy states of graphene triangular quantum dots in a magnetic field

{N}_{\mathrm{edge}}\ensuremath{\geqslant}12

Magnetic phases of graphene nanoribbons under potential fluctuations

. For a half-filled neutral shell we find spin-polarized ground state for structures up to