arXiv subjects

V. P. Gusynin

Publications and source records attributed to V. P. Gusynin.

At least 73 records · Page 4Linked to original sources

arXiv2008

Dynamics in the quantum Hall effect and the phase diagram of graphene

The dynamics responsible for lifting the degeneracy of the Landau levels in the quantum Hall (QH) effect in graphene is studied by utilizing a low-energy effective model with a contact interaction. A detailed analysis of the solutions of the gap equation for Dirac quasiparticles is performed at both zero and nonzero temperatures. The characteristic feature of the solutions is that the order parameters connected with the QH ferromagnetism and magnetic catalysis scenarios necessarily coexist. The solutions reproduce correctly the experimentally observed novel QH plateaus in graphene in strong magnetic fields. The phase diagram of this system in the plane of temperature and electron chemical potential is analyzed. The phase transitions corresponding to the transitions between different QH plateaus in graphene are described.

cond-mat.mes-hall↗

arXiv2008

Edge states, mass and spin gaps, and quantum Hall effect in graphene

Motivated by recent experiments and a theoretical analysis of the gap equation for the propagator of Dirac quasiparticles, we assume that the physics underlying the recently observed removal of sublattice and spin degeneracies in graphene in a strong magnetic field is connected with the generation of both Dirac masses and spin gaps. The consequences of such a scenario for the existence of the gapless edge states with zigzag and armchair boundary conditions are discussed. In the case of graphene on a half-plane with a zigzag edge, there are gapless edge states in the spectrum only when the spin gap dominates over the mass gap. In the case of an armchair edge, however, the existence of the gapless edge states depends on the specific type of mass gaps.

cond-mat.mes-hall↗

arXiv2007

AC conductivity of graphene: from tight-binding model to 2+1-dimensional quantum electrodynamics

We consider the relationship between the tight-binding Hamiltonian of the two-dimensional honeycomb lattice of carbon atoms with nearest neighbor hopping only and the 2+1 dimensional Hamiltonian of quantum electrodynamics which follows in the continuum limit. We pay particular attention to the symmetries of the free Dirac fermions including spatial inversion, time reversal, charge conjugation and chirality. We illustrate the power of such a mapping by considering the effect of the possible symmetry breaking which corresponds to the creation of a finite Dirac mass, on various optical properties. In particular, we consider the diagonal AC conductivity with emphasis on how the finite Dirac mass might manifest itself in experiment. The optical sum rules for the diagonal and Hall conductivities are discussed.

cond-mat.mes-hall↗

arXiv2007

Gap generation for Dirac fermions on Lobachevsky plane in a magnetic field

We study symmetry breaking and gap generation for fermions in the 2D space of constant negative curvature (the Lobachevsky plane) in an external covariantly constant magnetic field in a four-fermion model. It is shown that due to the magnetic and negative curvature catalysis phenomena the critical coupling constant is zero and there is a symmetry breaking condensate in the chiral limit even in free theory. We analyze solutions of the gap equation in the cases of zero, weak, and strong magnetic fields. As a byproduct we calculate the density of states and the Hall conductivity for noninteracting fermions that may be relevant for studies of graphene.

hep-ph↗

arXiv2007

Magneto-optical conductivity in Graphene

Landau level quantization in graphene reflects the Dirac nature of its quasiparticles and has been found to exhibit an unusual integer quantum Hall effect. In particular the lowest Landau level can be thought as shared equally by electrons and holes and this leads to characteristic behaviour of the magneto-optical conductivity as a function of frequency $Ω$ for various values of the chemical potential $μ$. Particular attention is paid to the optical spectral weight under various absorption peaks and its redistribution as $μ$ is varied. We also provide results for magnetic field $B$ as well as chemical potential sweeps at selected fixed frequencies which can be particularly useful for possible measurements in graphene. Both diagonal and Hall conductivity are considered.

cond-mat.mes-hall↗

arXiv2007

Sum Rules for the Optical and Hall Conductivity in Graphene

Graphene has two atoms per unit cell with quasiparticles exhibiting the Dirac-like behavior. These properties lead to interband in addition to intraband optical transitions and modify the $f$-sum rule on the longitudinal conductivity. The expected dependence of the corresponding spectral weight on the applied gate voltage $V_g$ in a field effect graphene transistor is $\sim {const}- |V_g|^{3/2}$. For $V_g =0$, its temperature dependence is $T^3$ rather than the usual $T^2$. For the Hall conductivity, the corresponding spectral weight is determined by the Hall frequency $ω_H$ which is linear in the carrier imbalance density $ρ$, and hence proportional to $V_g$, and is different from the cyclotron frequency for Dirac quasiparticles.

cond-mat.mes-hall↗

arXiv2007

Anomalous Absorption Line in the Magneto-Optical Response of Graphene

The intensity as well as position in energy of the absorption lines in the infrared conductivity of graphene, both exhibit features that are directly related to the Dirac nature of its quasiparticles. We show that the evolution of the pattern of absorption lines as the chemical potential is varied encodes the information about the presence of the anomalous lowest Landau level. The first absorption line related to this level always appears with full intensity or is entirely missing, while all other lines disappear in two steps. We demonstrate that if a gap develops, the main absorption line splits into two provided that the chemical potential is greater than or equal to the gap.

cond-mat.str-el↗

arXiv2006

Excitonic gap, phase transition, and quantum Hall effect in graphene: strong-coupling regime

We suggest that physics underlying the recently observed removal of sublattice and spin degeneracies in graphene in a strong magnetic field describes a phase transition connected with the generation of excitonic and spin gaps. The strong-coupling regime is described using a phenomenological model with enhanced Zeeman splitting (spin gap) and excitonic gaps. The experimental form of the Hall conductivity $σ_{xy}$ with the additional $ν= 0, \pm 1$ plateaus is reproduced. The form of $σ_{xy}$ in the case of a strong-coupling regime with no enhanced Zeeman splitting is also discussed.

cond-mat.str-el↗

arXiv2006

Excitonic gap, phase transition, and quantum Hall effect in graphene

We suggest that physics underlying the recently observed removal of sublattice and spin degeneracies in graphene in a strong magnetic field describes a phase transition connected with the generation of an excitonic gap. The experimental form of the Hall conductivity is reproduced and the main characteristics of the dynamics are described. Predictions of the behavior of the gap as a function of temperature and a gate voltage are made.

cond-mat.str-el↗

arXiv2006

Transport of Dirac quasiparticles in graphene: Hall and optical conductivities

The analytical expressions for both diagonal and off-diagonal ac and dc conductivities of graphene placed in an external magnetic field are derived. These conductivities exhibit rather unusual behavior as functions of frequency, chemical potential and applied field which is caused by the fact that the quasiparticle excitations in graphene are Dirac-like. One of the most striking effects observed in graphene is the odd integer quantum Hall effect. We argue that it is caused by the anomalous properties of the Dirac quasiparticles from the lowest Landau level. Other quantities such as Hall angle and Nernst signal also exhibit rather unusual behavior, in particular when there is an excitonic gap in the spectrum of the Dirac quasiparticle excitations.

cond-mat.mes-hall↗

arXiv2006

Unusual Microwave Response of Dirac Quasiparticles in Graphene

Recent experiments have proven that the quasiparticles in graphene obey a Dirac equation. Here we show that microwaves are an excellent probe of their unusual dynamics. When the chemical potential is small the intraband response can exhibit a cusp around zero frequency $Ω$ and this unusual lineshape changes to Drude-like by increasing the chemical potential $|μ|$, with width also increasing linearly with $μ$. The interband contribution at T=0 is a constant independent of $Ω$ with a lower cutoff at $2 μ$. Distinctly different behavior occurs if interaction-induced phenomena in graphene cause an opening of a gap $Δ$. At large magnetic field $B$, the diagonal and Hall conductivities at small $Ω$ become independent of $B$ but remain nonzero and show structure associated with the lowest Landau level. This occurs because in the Dirac theory the energy of this level, $E_0 = \pm Δ$, is field independent in sharp contrast to the conventional case.

cond-mat.str-el↗

arXiv2005

Unconventional Integer Quantum Hall effect in graphene

Monolayer graphite films, or graphene, have quasiparticle excitations that can be described by 2+1 dimensional Dirac theory. We demonstrate that this produces an unconventional form of the quantized Hall conductivity $σ_{xy} = - (2 e^2/h)(2n+1)$ with $n=0,1,...$, that notably distinguishes graphene from other materials where the integer quantum Hall effect was observed. This unconventional quantization is caused by the quantum anomaly of the $n=0$ Landau level and was discovered in recent experiments on ultrathin graphite films.

cond-mat.mes-hall↗

arXiv2005

Magnetic oscillations in planar systems with the Dirac-like spectrum of quasiparticle excitations II: transport properties

The quantum magnetic oscillations of electrical (Shubnikov de Haas effect) and thermal conductivities are studied for graphene which represents a distinctive example of planar systems with a linear, Dirac-like spectrum of quasiparticle excitations. We show that if a utmost care was taken to separate electron and phonon contributions in the thermal conductivity, the oscillations of electron thermal conductivity, $κ(B)$ and the Lorenz number, $L(B)$ would be observable in the low field (less than a few Teslas) regime.

cond-mat.str-el↗

arXiv2004

Surprises in nonperturbative dynamics in sigma-model at finite density

The linear $SU(2)_L \times SU(2)_R$ sigma-model occupies a unique place in elementary particle physics and quantum field theory. It has been recently realized that when a chemical potential for hypercharge is added, it becomes a toy model for the description of the dynamics of the kaon condensate in high density QCD. We review recent results in nonperturbative dynamics obtained in the ungauged and gauged versions of this model.

hep-ph↗

arXiv2004

Magnetic oscillations in planar systems with the Dirac-like spectrum of quasiparticle excitations

The quantum magnetic oscillations are studied for planar condensed matter systems with a linear, Dirac-like spectrum of quasiparticle excitations. We derive analytical expressions for magnetic oscillations (de Haas - van Alphen effect) in the density of states, thermodynamic potential, magnetization and chemical potential both for zero and finite temperatures, and in the presence of scattering from impurities. We discuss also a possibility of using magnetic oscillations for detection of a gap that may open in the spectrum of quasiparticle excitations due to a nontrivial interaction between them.

cond-mat.str-el↗

arXiv2004

Thermal conductivity and competing orders in d-wave superconductors

We derive the expression for the thermal conductivity κin the low-temperature limit T \to 0 in d-wave superconductors, taking into account the presence of competing orders such as spin-density wave, is-pairing, etc.. The expression is used for analyzing recent experimental data in La_{2-x}Sr_xCuO_4. Our analysis strongly suggests that competing orders can be responsible for anomalies in behavior of thermal conductivity observed in those experiments.

cond-mat.str-el↗

arXiv2003

Spontaneous rotational symmetry breaking and roton like excitations in gauged sigma-model at finite density

The linear $σ$-model with a chemical potential for hypercharge is a toy model for the description of the dynamics of the kaon condensate in high density QCD. We analyze the dynamics of the gauged version of this model. It is shown that spontaneous breakdown of $SU(2) \times U(1)_{Y}$ symmetry, caused by the chemical potential, is always accompanied by spontaneous breakdown of both rotational symmetry and electromagnetic $U(1)_{em}$. The spectrum of excitations in this model is rich and, because of rotational symmetry breakdown, anisotropic. It is shown that there exist excitation branches that behave as phonon like quasiparticles for small momenta and as roton like ones for large momenta. This suggests that this model can be relevant for anisotropic superfluid systems.

hep-ph↗

arXiv2003

Infrared cutoff dependence of the critical flavor number in three-dimensional QED

We solve, analytically and numerically, a gap equation in parity invariant QED_3 in the presence of an infrared cutoff μand derive an expression for the critical fermion number N_c as a function of μ. We argue that this dependence of N_c on the infrared scale might solve the discrepancy between continuum Schwinger-Dyson equations studies and lattice simulations of QED_3.

hep-ph↗