arXiv subjects

Ioannis Kleftogiannis

Publications and source records attributed to Ioannis Kleftogiannis.

22 records · Page 2Linked to original sources

arXiv2014

Edge states versus diffusion in disordered graphene flakes

We study the localization properties of the wavefunctions in graphene flakes with short range disorder, via the numerical calculation of the Inverse Participation Ratio($IPR$) and it scaling which provides the fractal dimension $D_{2}$. We show that the edge states which exist at the Dirac point of ballistic graphene (no disorder) with zig-zag edges survive in the presence of weak disorder with wavefunctions localized at the boundaries of the flakes. We argue, that there is a strong interplay between the underlying destructive interference mechanism of the honeycomb lattice of graphene leading to edge states and the diffusive interference mechanism introduced by the short-range disorder. This interplay results in a highly abnormal behavior, wavefunctions are becoming progressively less localized as the disorder is increased, indicated by the decrease of the average $\langle IPR\rangle$ and the increase of $D_{2}$. We verify, that this abnormal behavior is absent for graphene flakes with armchair edges which do not provide edge states.

cond-mat.mes-hall↗

arXiv2013

Conductance through disordered graphene nanoribbons: Standard and anomalous electron localization

Conductance fluctuations produced by the presence of disorder in zigzag and armchair graphene nanoribbons are studied. We show that quantum transport in zigzag nanoribbons takes place via edge states which are exponentially localized, as in the standard Anderson localization problem, whereas for armchair nanoribbons the symmetry of the graphene sublattices produces anomalous localization, or delocalization. We show that these two different electron localizations lead to significant differences of the conductance statistics between zigzag and armchair nanoribbons. In particular, armchair nanoribbons show nonconventional large conductance fluctuations relative to those of Anderson-localized electrons. We calculate analytically the complete distribution of conductances for both types of ribbons. Without free fitting parameters, we verify our theoretical results by performing numerical simulations of disordered zigzag and armchair nanoribbons of experimentally achievable lengths and widths.

cond-mat.mes-hall↗

arXiv2012

Conductance of 1D quantum wires with anomalous electron-wavefunction localization

We study the statistics of the conductance $g$ through one-dimensional disordered systems where electron wavefunctions decay spatially as $|ψ| \sim \exp (-λr^α)$ for $0 <α<1$, $λ$ being a constant. In contrast to the conventional Anderson localization where $|ψ| \sim \exp (-λr)$ and the conductance statistics is determined by a single parameter: the mean free path, here we show that when the wave function is anomalously localized ($α<1$) the full statistics of the conductance is determined by the average $<\ln g>$ and the power $α$. Our theoretical predictions are verified numerically by using a random hopping tight-binding model at zero energy, where due to the presence of chiral symmetry in the lattice there exists anomalous localization; this case corresponds to the particular value $α=1/2$. To test our theory for other values of $α$, we introduce a statistical model for the random hopping in the tight binding Hamiltonian.

cond-mat.mes-hall↗

arXiv2008

Scanning Gate Microscopy of a Nanostructure where Electrons Interact

We show that scanning gate microscopy can be used for probing electron-electron interactions inside a nanostructure. We assume a simple model made of two non-interacting strips attached to an interacting nanosystem. In one of the strips, the electrostatic potential can be locally varied by a charged tip. This change induces corrections upon the nanosystem Hartree-Fock self-energies which enhance the fringes spaced by half the Fermi wavelength in the images giving the quantum conductance as a function of the tip position.

cond-mat.mes-hall↗