arXiv subjects

A. V. Germanenko

Publications and source records attributed to A. V. Germanenko.

52 records · Page 3Linked to original sources

arXiv2002

Electron-electron interaction at decreasing $k_Fl$

The contribution of the electron-electron interaction to conductivity is analyzed step by step in gated GaAs/InGaAs/GaAs heterostructures with different starting disorder. We demonstrate that the diffusion theory works down to $k_F l\simeq 1.5-2$, where $k_F$ is the Fermi quasimomentum, $l$ is the mean free paths. It is shown that the e-e interaction gives smaller contribution to the conductivity than the interference independent of the starting disorder and its role rapidly decreases with $k_Fl$ decrease.

cond-mat.dis-nn↗

arXiv2001

Quantum corrections to conductivity: from weak to strong localization

Results of detailed investigations of the conductivity and Hall effect in gated single quantum well GaAs/InGaAs/GaAs heterostructures with two-dimensional electron gas are presented. A successive analysis of the data has shown that the conductivity is diffusive for $k_F l=25-2$ and behaves like diffusive one for $k_F l=2-0.5$ down to the temperature T=0.4 K. It has been therewith found that the quantum corrections are not small at low temperature when $k_F l\simeq 1$. They are close in magnitude to the Drude conductivity so that the conductivity $σ$ becomes significantly less than $e^{2}/h$ (the minimal $σ$ value achieved in our experiment is about $3\times 10^{-8}Ω^{-1}$ at $k_Fl\simeq 0.5$ and $T=0.46$ K). We conclude that the temperature and magnetic field dependences of conductivity in whole $k_Fl$ range are due to changes of quantum corrections.

cond-mat.dis-nn↗

arXiv2001

Role of doped layers in dephasing of 2D electrons in quantum well structures

The temperature and gate voltage dependences of the phase breaking time are studied experimentally in GaAs/InGaAs heterostructures with single quantum well. It is shown that appearance of states at the Fermi energy in the doped layers leads to a significant decrease of the phase breaking time of the carriers in quantum well and to saturation of the phase breaking time at low temperature.

cond-mat.soft↗

arXiv2001

Does theory of quantum correction to conductivity agree with experimental data in 2D systems?

The quantum correction to the conductivity have been studied in two types of 2D heterostructures: with doped quantum well and doped barriers. The consistent analysis shows that in the structures where electrons occupy the states in quantum well only, all the temperature and magnetic field dependencies of the components of resistivity tensor are well described by the theories of quantum corrections. The contribution of electron-electron interaction to the conductivity have been determined reliably in the structures with different electron density. A possible reason of large scatter in experimental data concerning the contribution of electron-electron interaction, obtained in previous papers, and the role of the carriers, occupied the states of the doped layers, is discussed.

cond-mat.dis-nn↗

arXiv2001

Weak localization in macroscopically inhomogeneous two-dimensional systems: a simulation approach

A weak-localization effect has been studied in macroscopically inhomogeneous 2D system. It is shown, that although the real phase breaking length tends to infinity when the temperature tends to zero, such a system can reveal a saturated behavior of the temperature dependence of that parameter, which is obtained from the standard analysis of the negative magnetoresistance and usually identified by experimentalists with the phase braking length.

cond-mat.dis-nn↗

arXiv2000

Low field negative magnetoresistance in double layer structures

The weak localization correction to the conductivity in coupled double layer structures is studied both experimentally and theoretically. Statistics of closed paths has been obtained from the analysis of magnetic field and temperature dependencies of negative magnetoresistance for magnetic field perpendicular and parallel to the structure plane. The comparison of experimental data with results of computer simulation of carrier motion over two 2D layers with scattering shows that inter-layers transitions play decisive role in the weak localization.

cond-mat.dis-nn↗

arXiv1999

New approach to analysis of negative magnetoresistance. The statistics of the closed paths

It is shown that a new kind of information can be extracted from the Fourier transform of negative magnetoresistance (MR) in 2D semiconductor structures. The procedure proposed provides the information on the area distribution function of the closed paths and on the area dependence of the mean length of closed paths $\bar{L} (S)$ . Based on this line of attack the method of analysis of the negative MR is suggested. The method is used for data treatment of negative MR in 2D structures. In previous version (cond-mat/9902038) we suppoused that the difference in area dependence of $\bar{L} (S)$ for structures investigated came from the difference in scattering ansotropy. The more detailed analysis shows that main reason for such difference is different relations between momentum and phase relaxation times.

cond-mat↗

arXiv1999

Statistics of closed paths in two-dimensional systems and negative magnetoresistance studied by computer simulation

Statistics of closed paths in two-dimensional systems, which just determines the interference quantum correction to conductivity and anomalous magnetoconductance, has been studied by computer simulation of a particle motion over the plane with randomly distributed scatters. Both ballistic and diffusion regimes have been considered. The results of simulation have been analyzed in the framework of diffusion approximation. They are used for calculation of the magnetic field dependence of magnetoconductance in the model 2D system. It is shown that the anomalous magnetoconductance can be in principle described by the well known expression, obtained in the diffusion approximation, but with the prefactor less than unity and phase breaking which differs from true value.

cond-mat.stat-mech↗

arXiv1999

Analysis of negative magnetoresistance. Statistics of closed paths. I. Theory

Statistics of closed paths in two-dimensional (2D) systems, which just determines the interference quantum correction to conductivity and anomalous magnetoconductance, has been studied by computer simulation of a particle motion over the plane with randomly distributed scatterers. Both ballistic and diffusion regimes have been considered. The results of simulation have been analyzed in the framework of diffusion approximation. They are used for calculation of the magnetic field dependence of magnetoconductance in the model 2D system. It is shown that the anomalous magnetoconductance can be in principle described by the well known expression, obtained in the diffusion approximation, but with the prefactor less than unity and phase breaking length which differs from true value.

cond-mat.dis-nn↗

arXiv1999

Analysis of negative magnetoresistance. Statistics of closed paths. II. Experiment

It is shown that a new kind of information can be extracted from the Fourier transform of negative magnetoresistance in 2D semiconductor structures. The procedure proposed provides the information on the area distribution function of closed paths and on the area dependence of the average length of closed paths. Based on this line of attack the method of analysis of the negative magnetoresistance is suggested. The method has been used to process the experimental data on negative magnetoresistance in 2D structures with different relations between the momentum and phase relaxation times. It is demonstrated this fact leads to distinction in the area dependence of the average length of closed paths.

cond-mat.dis-nn↗

arXiv1999

Magnetic-field-dependent zero-bias diffusive anomaly in Pb oxide-n-InAs structures: Coexistence of two- and three-dimensional states

The results of experimental and theoretical studies of zero-bias anomaly (ZBA) in the Pb-oxide-n-InAs tunnel structures in magnetic field up to 6T are presented. A specific feature of the structures is a coexistence of the 2D and 3D states at the Fermi energy near the semiconductor surface. The dependence of the measured ZBA amplitude on the strength and orientation of the applied magnetic field is in agreement with the proposed theoretical model. According to this model, electrons tunnel into 2D states, and move diffusively in the 2D layer, whereas the main contribution to the screening comes from 3D electrons.

cond-mat.mes-hall↗

arXiv1999

Anomalous magnetoconductance due to weak localization in 2D systems with anisotropic scattering: computer simulation

The results of computer simulation of particle motion over the plane with randomly distributed scatters are presented. They are used to analyse the influence of scattering anisotropy on the negative magnetoresistance due to weak localisation. It is shown that the magnetic field dependence of magnetoresistance in this case can be described by the well known expression, obtained in the diffusion limit for isotropic scatternig, but with the prefactor less than unity and breaking-phase length which differs from the true value.

cond-mat↗

arXiv1999

The new line of attack of analyses of NMR in 2D structures

There was shown that Fourier transform of the negative magnetoresistance (NMR) which is due to interference correction to the conductivity contains the information about the area distribution function of the closed paths and about area dependence of the mean length of closed paths \bar{L}(S). Based on this line of attack we suggest the method of analysis of NMR and use it for data treatment of the NMR in 2D structure with doped barrier. There was shown that in structure investigated \bar{L}(S)dependence is determined by the scattering anisotropy.

cond-mat↗

arXiv1996

Interband mixing between two-dimensional states localized in a surface quantum well and heavy hole states of the valence band in narrow gap semiconductor

Theoretical calculations in the framework of Kane model have been carried out in order to elucidate the role of interband mixing in forming the energy spectrum of two-dimensional carriers, localized in a surface quantum well in narrow gap semiconductor. Of interest was the mixing between the 2D states and heavy hole states in the volume of semiconductor. It has been shown that the interband mixing results in two effects: the broadening of 2D energy levels and their shift, which are mostly pronounced for semiconductors with high doping level. The interband mixing has been found to influence mostly the effective mass of 2D carriers for large their concentration, whereas it slightly changes the subband distribution in a wide concentration range.

cond-mat↗

arXiv1996

Spin-dependent tunneling in metal-insulator-narrow gap semiconductor structures in a magnetic field

We present results of tunneling studies of p-Hg_{1-x}Cd_{x}Te-oxide-Al structures with 0.165<x<0.2 in a magnetic field up to 6 T. The tunneling conductivity oscillations resulting from the Landau quantization of the energy spectrum in the semiconductor volume are investigated. Under an in-plane magnetic field the amplitudes of tunneling conductivity maxima connected with the tunneling into `a' and `b' spin sublevels are found to differ substantionally from one another, and the amplitude ratio varying from structure to structure. To understand the cause of this behavior, the tunneling conductivity for this magnetic field orientation is calculated taking into consideration the multi-band energy spectrum. It is shown that the contributions of the different spin-sublevels to the tunneling conductivity are dissimilar and the relationship between them depends strongly on the value of surface potential.

cond-mat↗

arXiv1996

Tunnelling Studies of Two-Dimensional States in Semiconductors with Inverted Band Structure: Spin-orbit Splitting, Resonant Broadening

The results of tunnelling studies of the energy spectrum of two-dimensional (2D) states in a surface quantum well in a semiconductor with inverted band structure are presented. The energy dependence of quasimomentum of the 2D states over a wide energy range is obtained from the analysis of tunnelling conductivity oscillations in a quantizing magnetic field. The spin-orbit splitting of the energy spectrum of 2D states, due to inversion asymmetry of the surface quantum well, and the broadening of 2D states at the energies, when they are in resonance with the heavy hole valence band, are investigated in structures with different strength of the surface quantum well. A quantitative analysis is carried out within the framework of the Kane model of the energy spectrum. The theoretical results are in good agreement with the tunnelling spectroscopy data.

cond-mat↗