arXiv subjects

G. L. Klimchitskaya

Publications and source records attributed to G. L. Klimchitskaya.

At least 91 records · Page 5Linked to original sources

arXiv2016

Casimir free energy and pressure for magnetic metal films

We examine the Casimir free energy and pressure of magnetic metal films, which are free-standing in vacuum, sandwiched between two dielectric plates, and deposited on either nonmagnetic or magnetic metallic plates. All calculations are performed using both the Drude and plasma model approaches to the Lifshitz theory. According to our results, the Casimir free energies and pressures calculated using both theoretical approaches are significantly different in the magnitude and sign even for thin films of several tens of nanometers thickness. Thus, for the Ni film of 47\,nm thickness deposited on a Fe plate the obtained magnitudes of the Casimir free energy differ by the factor of 5866. We show that the Casimir free energy and pressure of a magnetic film calculated using the plasma model approach do not possess the classical limit, but exponentially fast drop to zero with increasing film thickness. If the Drude model approach is used, the classical limit is reached for magnetic films of about 150\,nm thickness, but the Casimir free energy remains nonzero in the limit of ideal metal, contrary to expectations. For the plasma model approach the Casimir free energy of a film vanishes in this case. Numerical computations are performed for the magnetic films made of Ni, nonmagnetic plates made of Cu and Al, and magnetic plates made of Fe using the tabulated optical data for the complex indexes of refraction of all metals. The obtained results can be used for a discrimination between the plasma and Drude model approaches in the Casimir physics and in the investigation of stability of thin films.

quant-ph↗

arXiv2016

Conductivity of pure graphene: Theoretical approach using the polarization tensor

We obtain analytic expressions for the conductivity of pristine (pure) graphene in the framework of the Dirac model using the polarization tensor in (2+1)-dimensions defined along the real frequency axis. It is found that at both zero and nonzero temperature $T$ the in-plane and out-of-plane conductivities of graphene are equal to each other with a high precision and essentially do not depend on the wave vector. At $T=0$ the conductivity of graphene is real and equal to $σ_0=e^2/(4\hbar)$ up to small nonlocal corrections in accordance with many authors. At some fixed $T\neq 0$ the real part of the conductivity varies between zero at low frequencies $ω$ and $σ_0$ for optical $ω$. If $ω$ is fixed, the conductivity varies between $σ_0$ at low $T$ and zero at high $T$. The imaginary part of the conductivity of graphene is shown to depend on the ratio of $ω$ to $T$. In accordance to the obtained asymptotic expressions, at fixed $T$ it varies from infinity at $ω=0$ to a negative minimum value reached at some $ω$, and then approaches to zero with further increase of $ω$. At fixed $ω$ the imaginary part of the conductivity varies from zero at $T=0$, reaches a negative minimum at some $T$ and then goes to infinity together with $T$. The numerical computations of both the real and imaginary parts of the conductivity are performed. The above results are obtained in the framework of quantum electrodynamics at nonzero temperature and can be generalized for graphene samples with nonzero mass gap parameter and chemical potential.

cond-mat.mtrl-sci↗

arXiv2016

Reflectivity properties of graphene with nonzero mass-gap parameter

The reflectivity properties of graphene with nonzero mass-gap parameter are investigated in the framework of Dirac model using the polarization tensor in (2+1)-dimensional space-time. For this purpose, a more simple explicit representation for the polarization tensor along the real frequency axis is found. The approximate analytic expressions for the polarization tensor and for the reflectivities of graphene are obtained in different frequency regions at any temperature. We show that the nonzero mass-gap parameter has a profound effect on the reflectivity of graphene. Specifically, at zero temperature the reflectivity of gapped graphene goes to zero with vanishing frequency. At nonzero temperature the same reflectivities are equal to unity at zero frequency. We also find the resonance behavior of the reflectivities of gapped graphene at both zero and nonzero temperature at the border frequency determined by the width of the gap. At nonzero temperature the reflectifities of graphene drop to zero in the vicinity of some frequency smaller than the border frequency. Our analytic results are accompanied with numerical computations performed over a wide frequency region. The developed formalism can be used in devising nanoscale optical detectors, optoelectronic switches and in other optical applications of graphene.

cond-mat.mes-hall↗

arXiv2016

Characteristic properties of the Casimir free energy for metal films deposited on metallic plates

The Casimir free energy and pressure of thin metal films deposited on metallic plates are considered using the Lifshitz theory and the Drude and plasma model approaches to the role of conduction electrons. The bound electrons are taken into account by using the complete optical data of film and plate metals. It is shown that for films of several tens of nanometers thickness the Casimir free energy and pressure calculated using these approaches differ by hundreds and thousands percent and can be easily discriminated experimentally. According to our results, the free energy of a metal film does not vanish in the limiting case of ideal metal if the Drude model approach is used in contradiction with the fact that the fluctuating field cannot penetrate in its interior. Numerical computations of the Casimir free energy and pressure of Ag and Au films deposited on Cu and Al plates have been performed using both theoretical approaches. It is shown that the free energy of a film can be both negative and positive depending on the metals used. For a Au film on a Ag plate and vice versa the Casimir energy of a film changes its sign with increasing film thickness. Applications of the obtained results for resolving the Casimir puzzle and the problem of stability of thin films are discussed.

quant-ph↗

arXiv2016

Quantum field theoretical description for the reflectivity of graphene

We derive the polarization tensor of graphene at nonzero temperature in (2+1)-dimensional space-time. The obtained tensor coincides with the previously known one at all Matsubara frequencies, but, in contrast to it, admits analytic continuation to the real frequency axis satisfying all physical requirements. Using the obtained representation for the polarization tensor, we develope quantum field theoretical description for the reflectivity of graphene. The analytic asymptotic expressions for the reflection coefficients and reflectivities at low and high frequencies are derived for both independent polarizations of the electromagnetic field. The dependencies of reflectivities on the frequency and angle of incidence are investigated. Numerical computations using the exact expressions for the polarization tensor are performed and application regions for the analytic asymptotic results are determined.

cond-mat.mes-hall↗

arXiv2016

Theory of reflectivity properties of graphene-coated material plates

The theoretical description for the reflectivity properties of dielectric, metal and semiconductor plates coated with graphene is developed in the framework of the Dirac model. Graphene is described by the polarization tensor allowing the analytic continuation to the real frequency axis. The plate materials are described by the frequency-dependent dielectric permittivities. The general formulas for the reflection coefficients and reflectivities of the graphene-coated plates, as well as their asymptotic expressions at high and low frequencies, are derived. The developed theory is applied to the graphene-coated dielectric (fused silica), metal (Au and Ni), and semiconductor (Si with various charge carrier concentrations) plates. In all these cases the impact of graphene coating on the plate reflectivity properties is calculated over the wide frequency ranges. The obtained results can be used in many applications exploiting the graphene coatings, such as the optical detectors, transparent conductors, anti-reflection surfaces etc.

cond-mat.mtrl-sci↗

arXiv2016

Quantum field theory of the Casimir force for graphene

We present theoretical description of the Casimir interaction in graphene systems which is based on the Lifshitz theory of dispersion forces and the formalism of the polarization tensor in (2+1)-dimensional space-time. The representation for the polarization tensor of graphene allowing the analytic continuation to the whole plane of complex frequencies is given. This representation is used to obtain simple asymptotic expressions for the reflection coefficients at all Matsubara frequencies and to investigate the origin of large thermal effect in the Casimir force for graphene. The developed theory is shown to be in a good agreement with the experimental data on measuring the gradient of the Casimir force between a Au-coated sphere and a graphene-coated substrate. The possibility to observe the thermal effect for graphene due to a minor modification of the already existing experimental setup is demonstrated.

quant-ph↗

arXiv2015

The van der Waals and Casimir energy of anisotropic atomically thin metallic films

We discuss the van der Waals (Casimir) free energies and pressures of thin metallic films, consisting from one to fifteen atomic layers, with regard to the anisotropy in their dielectric properties. Both free-standing films and films deposited on a dielectric substrate are considered. The computations are performed for a Au film and a sapphire substrate. According to our results, for free-standing Au films consisting of one and three atomic layers the respective relative error arising from the use of an isotropic (bulk) dielectric permittivity is equal to 73% and 37% for the van der Waals energy, and 70% and 35% for the pressure. We tabulate the energy and pressure van der Waals coefficients of thin Au films computed with account of their anisotropy. It is shown that the bulk permittivity of Au can be used for the films consisting of more than 30 atomic layers, i.e., more than approximately 7 nm thickness. The role of relativistic effects is also investigated and shown to be important even for the films consisting of two or three layers. The obtained results can find applications in the investigation of stability of thin films and development of novel nanoscale devices.

cond-mat.other↗

arXiv2015

Casimir free energy of metallic films: Discriminating between Drude and plasma model approaches

We investigate the Casimir free energy of a metallic film either sandwiched between two dielectric plates or in vacuum. It is shown that even for a thin film of several tens of nanometer thickness the Casimir free energy and pressure calculated with the Lifshitz theory using the Drude model and the plasma model approaches take significantly different values and can be easily discriminated. According to our results, the classical limit is already achieved for films of about 100\,nm thickness if the Drude model approach is used in calculations. In this case the classical expressions for the Casimir free energy and pressure are common for both configurations considered. If the plasma model approach is used, the classical limit is not achieved for any film thickness. Instead, the Casimir free energy and pressure are decreasing exponentially to zero. When the plasma frequency goes to infinity, the Casimir free energy obtained using the Drude model approach goes to a nonzero limit in contradiction with expectations. If the plasma model approach is used the free energy of metallic film goes to zero in the limit of infinitely large plasma frequency. All analytic results are accompanied by numerical computations performed for a Au film and sapphire plates. The possibilities to observe the predicted effects discriminating between the Drude and plasma model approaches are discussed.

quant-ph↗

arXiv2015

Analytic results for the Casimir free energy between ferromagnetic metals

We derive perturbation analytic expressions for the Casimir free energy and entropy between two dissimilar ferromagnetic plates which are applicale at arbitrarily low temperature. The dielectric properties of metals are described using either the nondissipative plasma model or the Drude model taking into account the dissipation of free charge carriers. Both cases of constant and frequency-dependent magnetic permeability are considered. It is shown that for ferromagnetic metals described by the plasma model the Casimir entropy goes to zero when the temperature vanishes, i.e., the Nernst heat theorem is satisfied. For ferromagnetic metals with perfect crystal lattices described by the Drude model the Casimir entropy goes to a nonzero constant depending on the parameters of a system with vanishing temperature, i.e., the Nernst heat theorem is violated. This constant can be positive which is quite different from the earlier investigated case of two nonmagnetic metals.

quant-ph↗

arXiv2015

Casimir and van der Waals forces: Advances and problems

We review modern achievements and problems in physics of the van der Waals and Casimir forces which arise due to zero-point and thermal fluctuations of the electromagnetic field between closely spaced material surfaces. This subject attracted great experimental and theoretical attention during the last few years because the fluctuation-induced forces find a lot of applications in both fundamental physics and nanotechnology. After a short introduction to the subject, we describe main experimental and theoretical results obtained in the field during the last fifteen years. In the following presentation, we discuss some of the recent results by the authors and their collaborators which are of high promise for future developments. Specifically, we consider new features of the Casimir force acting between a gold sphere and an indium tin oxide plate, present the experimental and theoretical results on measuring the Casimir interaction between two gold surfaces by means of dynamic atomic force microscope, and outline first measurements of the Casimir interaction between magnetic surfaces and related theory. Special attention is devoted to the Casimir effect for graphene, which is the prospective material for microelectromechanical devices of next generations.

quant-ph↗

arXiv2015

Origin of large thermal effect in the Casimir interaction between two graphene sheets

Using the recently derived representation for the polarization tensor in (2+1)-dimensional space-time allowing an analytic continuation to the entire plane of complex frequencies, we obtain simple analytic expressions for the reflection coefficients of graphene at nonzero Matsubara frequencies. In the framework of the Lifshitz theory, these coefficients are shown to lead to nearly exact results for the Casimir free energy and pressure between two graphene sheets. The constituent parts of large thermal effect, arising in the Casimir interaction at short separations due to an explicit parametric dependence of the polarization tensor on the temperature and an implicit dependence through a summation over the Matsubara frequencies, are calculated. It is demonstrated that an explicit thermal effect exceeds an implicit one at shorter separations, both effects are similar in magnitudes at moderate separations, and that an implicit effect becomes a larger one with further increase of separation. Possible applications of the developed formalism, other than the Casimir effect, are discussed.

cond-mat.other↗

arXiv2015

Improved constraints on the coupling constants of axion-like particles to nucleons from recent Casimir-less experiment

We obtain improved constraints on the coupling constants of axion-like particles to nucleons from a recently performed Casimir-less experiment. For this purpose, the differential force between a Au-coated sphere and either Au or Si sectors of a rotating disc, arising due to two-axion exchange, is calculated. Over a wide region of axion masses from 1.7 meV to 0.9 eV the obtained constraints are stronger up to a factor of 60 than the previously known ones following from the Cavendish-type experiment and measurements of the effective Casimir pressure.

hep-ph↗

arXiv2015

Constraints on axion and corrections to Newtonian gravity from the Casimir effect

Axion is a light pseudoscalar particle of much interest for physics of elementary particles and for astrophysics. We review the recently obtained constraints on axion to nucleon coupling constants following from different experiments on measuring the Casimir interaction. These constraints are compared with those following from other laboratory experiments within the wide range of masses of axion-like particles from 10^{-10} to 20 eV. We also collect the most strong constraints on the Yukawa-type and power-type corrections to the Newton law of gravitation which follow from measurements of the Casimir interaction, Eotvos- and Cavendish-type experiments. The possibility to obtain stronger constraints on an axion from the Casimir effect is proposed.

hep-ph↗

arXiv2015

Comparison of hydrodynamic model of graphene with recent experiment on measuring the Casimir interaction

We obtain the reflection coefficients from a graphene sheet deposited on a material substrate under a condition that graphene is described by the hydrodynamic model. Using these coefficients, the gradient of the Casimir force in the configuration of recent experiment is calculated in the framework of the Lifshitz theory. It is shown that the hydrodynamic model is excluded by the measurement data at the 99% confidence level over a wide range of separations. From the fact that the same data are in a very good agreement with theoretical predictions of the Dirac model of graphene, the low-energy character of the Casimir interaction is confirmed.

cond-mat.other↗

arXiv2014

Casimir entropy for magnetodielectrics

We find the analytic expressions for the Casimir free energy, entropy and pressure at low temperature in the configuration of two parallel plates made of magnetodielectic material. The cases of constant and frequency-dependent dielectic permittivity and magnetic permeability of the plates are considered. Special attention is paid to the account of dc conductivity. It is shown that in the case of finite static dielectric permittivity and magnetic permeability the Nernst heat theorem for the Casimir entropy is satisfied. If the dc conductivity is taken into account, the Casimir entropy goes to a positive nonzero limit depending on the parameters of a system when the temperature vanishes, i.e., the Nernst theorem is violated. The experimental situation is also discussed.

quant-ph↗

arXiv2014

Constraints on axion-nucleon coupling constants from measuring the Casimir force between corrugated surfaces

We obtain stronger laboratory constraints on the coupling constants of axion-like particles to nucleons from measurements of the normal and lateral Casimir forces between sinusoidally corrugated surfaces of a sphere and a plate. For this purpose, the normal and lateral additional force arising in the experimental configurations due to two-axion exchange between protons and neutrons are calculated. Our constraints following from measurements of the normal and lateral Casimir forces are stronger than the laboratory constraints reported so far for masses of axion-like particles larger than 11eV and 8eV, respectively. A comparison between various laboratory constraints on the coupling constants of axion-like particles to nucleons obtained from the magnetometer measurements, Eotvos- and Cavendish-type experiments, and from the Casimir effect is performed over the wide range of masses of axion-like particles from 10^{-10}eV to 20eV.

hep-ph↗

arXiv2014

Impact of graphene coating on the atom-plate interaction

Using the recently proposed quantum electrodynamical formalism, we calculate the Casimir-Polder free energies and forces between the ground state atoms of Rb, Na, Cs and He${}^{\ast}$ and the plates made of Au, Si, sapphire and fused silica coated with a graphene sheet. It is shown that the graphene coating has no effect on the Casimir-Polder interaction for metallic plates, but influences significantly for plates made of dielectric materials. The influence of graphene coating increases with decreasing static dielectric permittivity of the plate material and the characteristic frequency of an atomic dynamic polarizability. Simple analytic expressions for the classical limit of the Casimir-Polder free energy and force between an atom and a graphene-coated plate are obtained. From the comparison with the results of numerical computations, the application region of these expressions is determined.

quant-ph↗