arXiv subjects

L. A. Falkovsky

Publications and source records attributed to L. A. Falkovsky.

At least 19 recordsLinked to original sources

arXiv2014

Structure and electron bands of phosphorus allotropes

The small difference between the rhombohedral phosphorus lattice ($A$-7 phase) and the simple cubic phase as well as between phosphorene and the cubic structure is used in order to construct their quasiparticle band dispersion. We exploit the Peierls idea of the Brillouin zone doubling, which has been previously employed in consideration of semimetals of the $V$ period and $IV$--$VI$ semiconductors. In the common framework, individual properties of phosphorus allotropes are revealed.

cond-mat.mes-hall↗

arXiv2014

Effect of electron-phonon interactions on Raman line at ferromagnetic ordering

The theory of Raman scattering in half-metals by optical phonons interacting with conduction electrons is developed. We evaluate the effect of electron-phonon interactions at ferromagnetic ordering in terms of the Boltzmann equation for carriers. The chemical potential is found to decrease with temperature decreasing. Both the linewidth and frequency shift exhibit a dependence on temperature.

cond-mat.mtrl-sci↗

arXiv2013

Influence of ferromagnetic ordering on Raman scattering in CoS$_2$

The effects of phonon anharmonicity, phonon-magnon and electron-phonon interactions on the temperature dependence of Raman optical phonon modes are theoretically investigated. Besides of the Klemens result for the phonon width due to anharmonicity, the corresponding lineshift is derived. We argue that the phonon decay into two magnons has very low intensity in ferromagnets with low Curie temperatures. Therefore, the electron interband transitions accompanied with the ferromagnetic ordering are included in considerations to get a good quantitative agreement with experiments.

cond-mat.str-el↗

arXiv2013

Thermodynamics of electron-hole liquids in graphene

The impact of renormalization of the electron spectrum on the chemical potential, heat capacity, and oscillating magnetic moment is studied. The cases of low and high temperatures are considered. At low temperatures, doped graphene behaves as the usual Fermi liquids with the power temperature laws for thermodynamic properties. However, at high temperatures and relatively low carrier concentrations, it exhibits the collective electron-holes features: the chemical potential tends to its value in the undoped case going with the temperature to the charge neutrality point. Simultaneously, the electron contribution into the heat capacity tends to the constant value, as in the case of the Boltzmann statistics.

cond-mat.mes-hall↗

arXiv2012

Quantum magneto-optics of graphite family

The optical conductivity of graphene, bilayer graphene, and graphite in quantizing magnetic fields is studied. Both dynamical conductivities, longitudinal and Hall's, are analytically evaluated. The conductivity peaks are explained in terms of electron transitions. We have shown that trigonal warping can be considered within the perturbation theory for strong magnetic fields larger than 1 T and in the semiclassical approach for weak fields when the Fermi energy is much larger than the cyclotron frequency. The main optical transitions obey the selection rule with \Deltan = 1 for the Landau number n, however the \Deltan = 2 transitions due to the trigonal warping are also possible. The Faraday/Kerr rotation and light transmission/reflection in the quantizing magnetic fields are calculated. Parameters of the Slonczewski-Weiss-McClure model are used in the fit taking into account the previous dHvA measurements and correcting some of them for the case of strong magnetic fields.

cond-mat.mes-hall↗

arXiv2012

Berry phase, semiclassical quantization and Landau levels

We propose the semiclassical quantization for complicated electron systems governed by a many-band Hamiltonian. An explicit analytical expression of the corresponding Berry phase is derived. This impact allows us to evaluate the Landau magnetic levels when the rigorous quantization fails, for instance, for bilayer graphene and graphite with the trigonal warping. We find that the magnetic breakdown can be observed for the certain type of classical electron orbits.

cond-mat.mes-hall↗

arXiv2011

Quantum magneto-optics of graphite with trigonal warping

The optical conductivity of graphite in quantizing magnetic fields is studied. Both the dynamical conductivities, longitudinal as well as Hall's, are analytically evaluated. The conductivity peaks are explained in terms of electron transitions. We have shown that the trigonal warping in graphite can be considered within the perturbation theory at the strong magnetic field larger than 1 T approximately. The main optical transitions obey the selection rule with $Δn=1$ for the Landau number $n$, however the $Δn=2$ transitions due to the trigonal warping with the small probability are also essential. The Kerr rotation and reflectivity in graphite in the quantizing magnetic fields are calculated. Parameters of the Slonczewski--Weiss--McClure model are used in the fit taking into account the previous dHvA measurements and correcting some of them for the case of the strong magnetic fields.

cond-mat.mtrl-sci↗

arXiv2011

Cyclotron resonance and Faraday rotation in graphite

The optical conductivity of graphite in quantizing magnetic fields is analytically evaluated for frequencies in the range of 10--300 meV, where the electron relaxation processes can be neglected and the low-energy excitations at the "Dirac lines" are more essential. The conductivity peaks are explained in terms of the electron transitions in graphite. Conductivity calculated per one graphite layer tends on average to the universal conductivity of graphene while the frequency is larger than the Landau spacing. The (semi)metal-insulator transformation is possible under doping in high magnetic fields.

cond-mat.mtrl-sci↗

arXiv2010

Replay to "Comment on 'Screening in gated bilayer graphene' "

We discuss the physics of the tunable bandgap in bilayer graphene with the gate voltage and doping. A comparison with experimental data obtained by Kuzmenko et al [Phys. Rev. B \textbf{80}, 165406 (2009)] demonstrates the good agreement.

cond-mat.mes-hall↗

arXiv2010

Anisotropy of graphite optical conductivity

The graphite conductivity is evaluated for frequencies between 0.1 eV, the energy of the order of the electron-hole overlap, and 1.5 eV, the electron nearest hopping energy. The in-plane conductivity per single atomic sheet is close to the universal graphene conductivity $e^2/4\hbar$ and, however, contains a singularity conditioned by peculiarities of the electron dispersion. The conductivity is less in the $c-$direction by the factor of the order of 0.01 governed by electron hopping in this direction.

cond-mat.mes-hall↗

arXiv2010

Universal infrared conductivity of graphite

The conductivity of graphite is analytically evaluated in the range of 0.1-1.5 eV, where the electron relaxation processes can be neglected, and the low energy excitations at the "Dirac" points are most essential. The value of conductivity calculated per one graphite layer is close to the universal conductivity of graphene. The features of the conductivity are explained in terms of singularities of the electron dispersion in graphite.

cond-mat.mes-hall↗

arXiv2009

Gate-tunable bandgap in bilayer graphene

The tight-binding model of bilayer graphene is used to find the gap between the conduction and valence bands, as a function of both the gate voltage and as the doping by donors or acceptors. The total Hartree energy is minimized and the equation for the gap is obtained. This equation for the ratio of the gap to the chemical potential is determined only by the screening constant. Thus the gap is strictly proportional to the gate voltage or the carrier concentration in the absence of donors or acceptors. In the opposite case, where the donors or acceptors are present, the gap demonstrates the asymmetrical behavior on the electron and hole sides of the gate bias. A comparison with experimental data obtained by Kuzmenko et al demonstrates the good agreement.

cond-mat.mes-hall↗

arXiv2009

Screening in gated bilayer graphene

The tight-binding model of a graphene bilayer is used to find the gap between the conduction and valence bands, as a function of both the gate voltage and as the doping by donors or acceptors. The total Hartree energy is minimized and the equation for the gap is obtained. This equation for the ratio of the gap to the chemical potential is determined only by the screening constant. Thus the gap is strictly proportional to the gate voltage or the carrier concentration in the absence of donors or acceptors. In the opposite case, where the donors or acceptors are present, the gap demonstrates the asymmetrical behavior on the electron and hole sides of the gate bias.

cond-mat.mes-hall↗

arXiv2009

InN dielectric function from the midinfrared to the visible range

The dispersion of the dielectric function for wurtzite InN is analytically evaluated in the region near the fundamental energy gap. The real part of the dielectric function has a logarithmic singularity at the absorption edge. This results in the large contribution into the optical dielectric constant. For samples with degenerate carriers, the real part of the dielectric function is divergent at the absorption edge. The divergence is smeared with temperatures or relaxation rate. The imaginary part of the dielectric function has a plateau far away from the absorption onset.

cond-mat.mtrl-sci↗

arXiv2008

Optical properties of graphene

Reflectance and transmittance of graphene in the optical region are analyzed as a function of frequency, temperature, and carrier density. We show that the optical graphene properties are determined by the direct interband electron transitions. The real part of the dynamic conductivity in doped graphene at low temperatures takes the universal constant value, whereas the imaginary part is logarithmically divergent at the threshold of interband transitions.

cond-mat.mes-hall↗

arXiv2008

Features of interband absorption in narrow-gap semiconductors

For semiconductors and semimetals possessing a narrow gap between bands with different parity, the dispersion of the dielectric function is explicitly evaluated in the infrared region. The imaginary part of the dielectric function has a plateau above the absorption threshold for the interband electron transitions. The real part of the dielectric function has a logarithmic singularity at the threshold. This results in the large contribution into the dielectric constant for pure semiconductors at low frequencies. For samples with degenerate carriers, the real part of the dielectric function is divergent at the absorption threshold. This divergence is smeared with the temperature or the collision rate.

cond-mat.mtrl-sci↗

arXiv2008

Symmetry constraints on phonon dispersion in graphene

Taking into account the constraints imposed by the lattice symmetry, we calculate the phonon dispersion for graphene with interactions between the first, second, and third nearest neighbors in the framework of the Born--von Karman model. Analytical expressions obtained for the dispersion of the out-of-plane (bending) modes give the nonzero sound velocity. The dispersion of four in-plane modes is determined by coupled equations. Values of the force constants are found in fitting with frequencies at critical points and with elastic constants measured on graphite.

cond-mat.mes-hall↗

arXiv2007

Phonon dispersion in graphene

Taking into account the constraints imposed by the lattice symmetry, the phonon dispersion is calculated for graphene with interactions between the first and second nearest neighbors in the framework of the Born-von Karman model. Analytical expressions are obtained for the out-of-plane (bending) modes determined only by two force constants as well as for the in-plane modes with four force constants. Values of the force constants are found in fitting to elastic constants and Raman frequencies observed in graphite.

cond-mat.mes-hall↗