A.D. Güçlü

Publications of A.D. Güçlü

• Spin and electronic correlations in gated graphene quantum rings

  Authors: P. Potasz, A.D. Güçlü, P. Hawrylak

  05/2010;

  We present a theory of graphene quantum rings designed to produce degenerate shells of single particle states close to the Fermi level. We show that populating these shells with carriers using a gateWe present a theory of graphene quantum rings designed to produce degenerate shells of single particle states close to the Fermi level. We show that populating these shells with carriers using a gate leads to correlated ground states with finite total electronic spin. Using a combination of tight-binding and configuration interaction methods we predict ground state and total spin of the system as a function of the filling of the shell. We show that for smaller quantum rings, the spin polarization of the ground state at half filling depends strongly on the size of the system, but reaches a maximum value after reaching a critical size. Comment: 7 pages, 8 figures

• Magnetism and correlations in fractionally filled degenerate shells of graphene quantum dots.

  Authors: A D Güçlü, P Potasz, O Voznyy, M Korkusinski, P Hawrylak

  Physical review letters. 12/2009; 103(24):246805.

  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.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.

• Zero-energy states in triangular and trapezoidal graphene structures

  Authors: P. Potasz, A.D. Güçlü, P. Hawrylak

  10/2009;

  We derive analytical solutions for the zero-energy states of degenerate shell obtained as a singular eigenevalue problem found in tight-binding (TB) Hamiltonian of triangular graphene quantum dotsWe derive analytical solutions for the zero-energy states of degenerate shell obtained as a singular eigenevalue 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 (DFT) 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. Comment: 4 pages, 4 figures

• The maximum density droplet to lower density droplet transition in quantum dots

  Authors: A. D. Güçlü, C. J. Umrigar

  07/2005;

  We show that, Landau level mixing in two-dimensional quantum dot wave functions can be taken into account very effectively by multiplying the exact lowest Landau level wave functions by a JastrowWe show that, Landau level mixing in two-dimensional quantum dot wave functions can be taken into account very effectively by multiplying the exact lowest Landau level wave functions by a Jastrow factor which is optimized by variance minimization. The comparison between exact diagonalization and fixed phase diffusion Monte Carlo results suggests that the phase of the many-body wave functions are not affected much by Landau level mixing. We apply these wave functions to study the transition from the maximum density droplet state (incipient integer quantum Hall state with angular momentum L=N(N-1)/2) to lower density droplet states (L>N(N-1)/2).

• Electronic Shells of Dirac Fermions in Graphene Quantum Rings in a Magnetic Field

  Authors: P. Potasz, A.D. Güçlü, P. Hawrylak, Pawel Hawrylak

  We present results of tight binding calculations demonstrating existence of degenerate electronic shells of Dirac fermions in narrow, charge neutral graphene quantum rings. We predict removal ofWe present results of tight binding calculations demonstrating existence of degenerate electronic shells of Dirac fermions in narrow, charge neutral graphene quantum rings. We predict removal of degeneracy with finite magnetic field. We show, using a combination of tight binding and configuration interaction methods, that by filling a graphene ring with additional electrons this carbon based structure with half-filled shell acquires a finite magnetic moment. yes yes

• Excitonic absorption in gate-controlled graphene quantum dots

  Authors: A.D. Güçlü, P. Potasz, P. Hawrylak, Pawel Hawrylak

  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 isWe 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 terahertz, 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. yes yes

• Localization in an inhomogeneous quantum wire

  Authors: A. D. Güçlü, C. J. Umrigar, Hong Jiang, Harold U. Baranger

  Physical Review B, v.80, 201302(R)-1-201302(R)-4 (2009).

  We study interaction-induced localization of electrons in an inhomogeneous quasi-one-dimensional system — a wire with two regions, one at low density and the other high. Quantum Monte CarloWe study interaction-induced localization of electrons in an inhomogeneous quasi-one-dimensional system — a wire with two regions, one at low density and the other high. Quantum Monte Carlo techniques are used to treat the strong Coulomb interactions in the low-density region, where localization of electrons occurs. The nature of the transition from high to low density depends on the density gradient — if it is steep, a barrier develops between the two regions, causing Coulomb blockade effects. Ferromagnetic spin polarization does not appear for any parameters studied. The picture emerging is in good agreement with measurements of tunneling between wires.