6 research outputs found
Energy spectrum of graphene with adsorbed potassium atoms
No full text In the present work, we study the influence of adsorbed impurities, namely potassium atoms, on the energy spectrum of electrons in graphene. The electron states of the system are described in the frame of the self-consistent multiband strong-coupling model. It is shown that, at the ordered arrangement of potassium atoms corresponding to a minimum of the free energy, the gap arises in the energy spectrum of graphene. It is established that, at the potassium concentration such that the unit cell includes two carbon atoms and one potassium atom, the latter being placed on the graphene surface above a carbon atom at a distance of 0.286 nm, the energy gap is equal to [Formula: see text]0.25 eV. Such situation is realized if graphene is placed on a potassium support. </jats:p
Theory of Electron Correlation in Disordered Crystals
No full textThis paper presents a new method of describing the electronic spectrum and electrical conductivity of disordered crystals based on the Hamiltonian of electrons and phonons. Electronic states of a system are described by the tight-binding model. Expressions for Green’s functions and electrical conductivity are derived using the diagram method. Equations are obtained for the vertex parts of the mass operators of the electron–electron and electron–phonon interactions. A system of exact equations is obtained for the spectrum of elementary excitations in a crystal. This makes it possible to perform numerical calculations of the energy spectrum and to predict the properties of the system with a predetermined accuracy. In contrast to other approaches, in which electron correlations are taken into account only in the limiting cases of an infinitely large and infinitesimal electron density, in this method, electron correlations are described in the general case of an arbitrary density. The cluster expansion is obtained for the density of states and electrical conductivity of disordered systems. We show that the contribution of the electron scattering processes to clusters is decreasing, along with increasing the number of sites in the cluster, which depends on a small parameter
Influence of the ordering of impurities on the appearance of an energy gap and on the electrical conductance of graphene
No full textAbstractIn the one-band model of strong coupling, the influence of substitutional impurity atoms on the energy spectrum and electrical conductance of graphene is studied. It is established that the ordering of substitutional impurity atoms on nodes of the crystal lattice causes the appearance of a gap in the energy spectrum of graphene with width η|δ| centered at the point yδ, where η is the parameter of ordering, δ is the difference of the scattering potentials of impurity atoms and carbon atoms, and y is the impurity concentration. The maximum value of the parameter of ordering is
η
max
=
2
y
,
y
≤
1
/
2
. For the complete ordering of impurity atoms, the energy gap width equals
2
y
|
δ
|
. If the Fermi level falls in the region of the mentioned gap, then the electrical conductance
σ
α
α
→
0
at the ordering of graphene, i.e., the metal–dielectric transition arises. If the Fermi level is located outside the gap, then the electrical conductance increases with the parameter of order η by the relation
σ
α
α
~
(
y
2
−
1
4
η
2
)
−
1
. At the concentration
y
=
1
/
2
, as the ordering of impurity atoms η →1, the electrical conductance of graphene
σ
α
α
→
∞
, i.e., the transition of graphene in the state of ideal electrical conductance arises.</jats:p
