arXiv subjects

V. M. Apalkov

Publications and source records attributed to V. M. Apalkov.

29 records · Page 2Linked to original sources

arXiv2001

Two-subband system in quantizing magnetic field: Probing many-body gap by non-equilibrium phonons

We study the many-body effects in a two-subband quasi-two-dimensional electron system in a quantizing magnetic field at filling factor three. A manifestation of these effects in the phonon absorption spectroscopy is discussed. The electron system is mapped onto a two-level system with the separation between levels determined by the intersubband splitting and the cyclotron energy. The electron-electron interaction enhances the excitation gap, which exists at all values of the interlevel splitting. This results in a single-peak structure of the phonon absorption rate as a function of magnetic field, instead of the double-peak structure for non-interacting electrons.

cond-mat.mes-hall↗

arXiv2001

Tuning gaps and phases of a two-subband system in a quantizing magnetic field

In this work we study the properties of a two-subband quasi-two-dimensional electron system in a strong magnetic field when the electron filling factor is equal to four. When the cyclotron energy is close to the intersubband splitting the system can be mapped onto a four-level electron system with an effective filling factor of two. The ground state is either a ferromagnetic state or a spin-singlet state, depending on the values of the inter-level splitting and Zeeman energy. The boundaries between these phases are strongly influenced by the inter-electron interaction. A significant exchange-mediated enhancement of the excitation gap results in the suppression of the electron-phonon interaction. The rate of absorption of non-equilibrium phonons is calculated as a function of Zeeman energy and inter-subband splitting. The phonon absorption rate has two peaks as a function of intersubband splitting and has a step-like structure as a function of Zeeman energy.

cond-mat.mes-hall↗

arXiv2001

Random Resonators and Prelocalized Modes in Disordered Dielectric Films

Areal density of disorder-induced resonators with a high quality factor, $Q\gg 1$, in a film with fluctuating refraction index is calculated theoretically. We demonstrate that for a given $kl>1$, where $k$ is the light wave vector, and $l$ is the transport mean free path, when {\em on average} the light propagation is diffusive, the likelihood for finding a random resonator increases dramatically with increasing the correlation radius of the disorder. Parameters of {\em most probable} resonators as functions of $Q$ and $kl$ are found.

cond-mat.dis-nn↗

arXiv2001

Crossover Between Universality Classes in the Statistics of Rare Events in Disordered Conductors

The crossover from orthogonal to the unitary universality classes in the distribution of the anomalously localized states (ALS) in two-dimensional disordered conductors is traced as a function of magnetic field. We demonstrate that the microscopic origin of the crossover is the change in the symmetry of the underlying disorder configurations, that are responsible for ALS. These disorder configurations are of weak magnitude (compared to the Fermi energy) and of small size (compared to the mean free path). We find their shape explicitly by means of the direct optimal fluctuation method.

cond-mat.dis-nn↗

arXiv2001

Interaction of a quantum dot with an incompressible two-dimensional electron gas

We consider a system of a incompressible quantum Hall liquid in close proximity to a parabolic quantum dot containing a few electrons. We observe a significant influence of the interacting electrons in the dot on the excitation spectrum of the incompressible state in the electron plane. Our calculated charge density indicates that unlike in the case of an impurity, interacting electrons in the dot seem to confine the fractionally charged excitations in the incompressible liquid.

cond-mat.mes-hall↗

arXiv2001

Optical properties of a Quantum-Dot Cascade Structure

We report on our theoretical studies of the luminescence spectra of a quantum cascade laser where the quantum wells in the active regions are replaced by parabolic quantum dots. We analyze the influence of shape and size of the dots on the luminescence spectra. The emission spectra have interaction induced blueshift which increases almost linearly with increasing electron number. The blueshift is smaller for larger and non-circular dots. For large dots, shape of the emission line has weak dependence on the shape of quantum dots.

cond-mat.str-el↗

arXiv2000

Influence of disorder and a parallel magnetic field on a Quantum Cascade Laser

The luminescence spectra of a quantum cascade laser in a strong magnetic field is influenced significantly by the presence of disorder (charged or neutral) in the system. An externally applied magnetic field parallel to the electron plane causes a red shift of the luminescence peak in the absence of any disorder potential. Our results indicate that the disorder potential tends to cancel that red shift and causes a rapid decrease of the luminescence peak. A similar behavior was observed in a recent experiment on QCL in a parallel magnetic field.

cond-mat.mes-hall↗

arXiv2000

Magnetic field induced luminescence spectra in a quantum cascade laser

We report on our study of the luminescence spectra of a quantum cascade laser in the presence of an external magnetic field tilted from the direction perpendicular to the electron plane. The effect of the tilted field is to allow novel optical transitions because of the coupling of intersubband-cyclotron energies. We find that by tuning the applied field, one can get optical transitions at different energies that are as sharp as the zero-field transitions.

cond-mat.mes-hall↗

arXiv2000

Theory of the Half-Polarized Quantum Hall States

We report a theoretical analysis of the half-polarized quantum Hall states observed in a recent experiment. Our numerical results indicate that the ground state energy of the quantum Hall $ν= 2/3$ and $ν= 2/5$ states versus spin polarization has a downward cusp at half the maximal spin polarization. We map the two-component fermion system onto a system of excitons and describe the ground state as a liquid state of excitons with non-zero values of exciton angular momentum.

cond-mat.mes-hall↗

arXiv2000

Comment on ``Composite Fermion Hofstadter Problem: Partially Polarized Density Wave States in the $ν=2/5$ ...''

In a recent paper [Phys.Rev.Lett. 82, 3665 (1999)], magnetic field driven spin transitions in fractional quantum Hall (FQH) states were reported, and in particular, at filling factors 2/3 and 2/5, weak features were observed at half polarization. This would imply that the ground state energy is non-monotonic at half polarization. It was proposed in Ref.[Phys. Rev. Lett. 84, 350 (2000)] that the system is then a charge density wave (CDW) state of composite fermions with a subband gap that could explain the observed plateaus at half polarization. Similar CDW state is also expected at filling factor 2/3. Here we show that the proposed CDW state is not the half polirized ground state at these two filling factors.

cond-mat.mes-hall↗

arXiv1998

Internal sinks and the smoothing of the surface structure in solids under irradiation

We consider in the article the influence of the irradiation and the internal sinks of the point defects on the rate of the flattening of the surface structure in solids. The irradiation produces only the additional external sources of point defects(vacancies and interstitial atoms). The general system of equations is formulated. The solution of the system on the stationary stage of the process is found. It is shown that depending on the values of some parameters of the solid the irradiation can increase or decrease the rate of the surface flattening.

cond-mat.mtrl-sci↗