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A. V. Germanenko

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

At least 37 records · Page 2Linked to original sources
arXiv2010

Energy relaxation rate of 2D hole gas in GaAs/InGaAs/GaAs quantum well within wide range of conductivitiy

The nonohmic conductivity of 2D hole gas (2DHG) in single $GaAsIn_{0.2}Ga_{0.8}AsGaAs$ quantum well structures within the temperature range of 1.4 - 4.2K, the carrier's densities $p=(1.5-8)\cdot10^{15}m^{-2}$ and a wide range of conductivities $(10^{-4}-100)G_0$ ($G_0=e^2/π\,h$) was investigated. It was shown that at conductivity $σ>G_0$ the energy relaxation rate $P(T_h,T_L)$ is well described by the conventional theory (P.J. Price J. Appl. Phys. 53, 6863 (1982)), which takes into account scattering on acoustic phonons with both piezoelectric and deformational potential coupling to holes. At the conductivity range $0.01G_0<σ<G_0$ energy the relaxation rate significantly deviates down from the theoretical value. The analysis of $\frac{dP}{dσ}$ at different lattice temperature $T_L$ shows that this deviation does not result from crossover to the hopping conductivity, which occurs at $σ<10^{-2}$, but from the Pippard ineffectiveness.

cond-mat.dis-nn↗
arXiv2010

Analysis of homogeneity of 2D electron gas at decreasing of electron density

We investigate the gate voltage dependence of capacitance of a system gate - 2D electron gas (C-Vg). The abrupt drop of capacitance at decreasing concentration was found. The possible reasons of this drop, namely inhomogeneity of electron density distribution and serial resistance of 2D electron gas are discussed. Simultaneous analysis of gate voltage dependences of capacitance and resistance has shown that in heavily doped 2D systems the main role in the drop of capacitance at decreasing concentration plays the resistance of 2D gas. It is found that the investigated systems remains homogeneous down to the low temperature conductivity about (10^-2-10^-3)e^2/h.

cond-mat.mes-hall↗
arXiv2010

Dephasing and interwell transitions in double quantum well heterostructures

The interference quantum correction to the conductivity in the gated double quantum well Al$_x$Ga$_{1-x}$As/GaAs/Al$_x$Ga$_{1-x}$As structures is studied experimentally. The consistent analysis of the interference induced positive magnetoconductivity allows us to find the interwell transition time $τ_{12}$ and the electron dephasing time $τ_ϕ$. It has been obtained that $τ_{12}^{-1}$ resonantly depends on the difference between the electron densities in the wells as predicted theoretically. The dephasing times have been determined under the conditions when one and both quantum wells are occupied. The surprising result is that the $τ_ϕ$ value in the one well does not depend on the occupation of the other one.

cond-mat.dis-nn↗
arXiv2010

Low magnetic field anomaly of the Hall effect in disordered 2D systems: Interplay between weak localization and electron-electron interaction

The nonlinear behavior of the Hall resistivity at low magnetic fields in single quantum well GaAs/In$_x$Ga$_{1-x}$As/GaAs heterostructures with degenerated electron gas is studied. It has been found that this anomaly is accompanied by the weaker temperature dependence of the conductivity as compared with that predicted by the first-order theory of the quantum corrections to the conductivity. We show that both effects in strongly disordered systems stem from the second order quantum correction caused by the effect of weak localization on the interaction correction and vice versa. This correction contributes mainly to the diagonal component of the conductivity tensor, it depends on the magnetic field like the weak localization correction and on the temperature like the interaction contribution.

cond-mat.dis-nn↗
arXiv2009

Disorder and temperature renormalization of interaction contribution to the conductivity in two-dimensional In$_{x}$Ga$_{1-x}$As electron systems

We study the electron-electron interaction contribution to the conductivity of two-dimensional In$_{0.2}$Ga$_{0.8}$As electron systems in the diffusion regime over the wide conductivity range, $σ\simeq(1-150) G_0$, where $G_0=e^2/(2π^2\hbar)$. We show that the data are well described within the framework of the one-loop approximation of the renormalization group (RG) theory when the conductivity is relatively high, $σ\gtrsim 15 G_0$. At lower conductivity, the experimental results are found to be in drastic disagreement with the predictions of this theory. The theory predicts much stronger renormalization of the Landau's Fermi liquid amplitude, which controls the interaction in the triplet channel, than that observed experimentally. A further contradiction is that the experimental value of the interaction contribution does not practically depend on the magnetic field, whereas the RG theory forecasts its strong decrease due to decreasing diagonal component of the conductivity tensor in the growing magnetic field.

cond-mat.str-el↗
arXiv2008

Diffusion conductivity and weak localization in two-dimensional structures with electrostatically induced random antidots array

Results of experimental study of the weak localization phenomenon in 2D system with artificial inhomogeneity of potential relief are presented. It is shown that the shape of the magnetoconductivity curve is determined by the statistics of closed paths. The area distribution function of closed paths has been obtained using the Fourier transformation of the magnetoconductivity curves taken at different temperatures. The experimental results are found in a qualitative agreement with the results of computer simulation.

cond-mat.dis-nn↗
arXiv2007

Renormalization of hole-hole interaction at decreasing Drude conductivity

The diffusion contribution of the hole-hole interaction to the conductivity is analyzed in gated GaAs/In$_x$Ga$_{1-x}$As/GaAs heterostructures. We show that the change of the interaction correction to the conductivity with the decreasing Drude conductivity results both from the compensation of the singlet and triplet channels and from the arising prefactor $α_i<1$ in the conventional expression for the interaction correction.

cond-mat.dis-nn↗
arXiv2007

Interference induced metallic-like behavior of a two-dimensional hole gas in asymmetric GaAs/In$_{x}$Ga$_{1-x}$As/GaAs quantum well

The temperature and magnetic field dependences of the conductivity of the heterostructures with asymmetric In$_x$Ga$_{1-x}$As quantum well are studied. It is shown that the metallic-like temperature dependence of the conductivity observed in the structures investigated is quantitatively understandable within the whole temperature range, $T=0.4-20$ K. It is caused by the interference quantum correction at fast spin relaxation for 0.4 K$ < T < 1.5$ K. At higher temperatures, 1.5 K$ 4-6$ K, the metallic-like behavior is determined by the phonon scattering.

cond-mat.dis-nn↗
arXiv2006

Giant suppression of the Drude conductivity due to quantum interference in disordered two-dimensional systems

Temperature and magnetic field dependences of the conductivity in heavily doped, strongly disordered two-dimensional quantum well structures GaAs/In$_x$Ga$_{1-x}$As/GaAs are investigated within wide conductivity and temperature ranges. Role of the interference in the electron transport is studied in the regimes when the phase breaking length $L_ϕ$ crosses over the localization length $ξ\sim l\exp{(πk_Fl/2)}$ with lowering temperature, where $k_F$ and $l$ are the Fermi quasimomentum and mean free path, respectively. It has been shown that all the experimental data can be understood within framework of simple model of the conductivity over delocalized states. This model differs from the conventional model of the weak localization developed for $k_Fl\gg 1$ and $L_ϕ\llξ$ by one point: the value of the quantum interference contribution to the conductivity is restricted not only by the phase breaking length $L_ϕ$ but by the localization length $ξ$ as well. We show that just the quantity $(τ_ϕ^\ast)^{-1}=τ_ϕ^{-1}+τ_ξ^{-1}$ rather than $τ_ϕ^{-1}$, where $τ_ϕ\propto T^{-1}$ is the dephasing time and $τ_ξ\simτ\exp(πk_F l)$, is responsible for the temperature and magnetic field dependences of the conductivity over the wide range of temperature and disorder strength down to the conductivity of order $10^{-2} e^2/h$.

cond-mat.dis-nn↗
arXiv2006

Nonuniversality of the interference quantum correction to conductivity beyond the diffusion regime

Results of numerical simulation of the weak localization in two-dimensional systems in wide range of magnetic filed are presented. Three cases are analyzed: (i) the isotropic scattering and randomly distributed scatterers; (ii) the anisotropic scattering and randomly distributed scatterers; (iii) the isotropic scattering and the correlated distribution of the scatterers. It is shown that the behavior of the conductivity beyond the diffusion regime strongly depends on the scattering anisotropy and correlation in the scatterer distribution.

cond-mat.dis-nn↗
arXiv2005

Diffusion and ballistic contributions of the interaction correction to the conductivity of a two-dimensional electron gas

The results of an experimental study of interaction quantum correction to the conductivity of two-dimensional electron gas in A$_3$B$_5$ semiconductor quantum well heterostructures are presented for a wide range of $Tτ$-parameter ($Tτ\simeq 0.03-0.8$), where $τ$ is the transport relaxation time. A comprehensive analysis of the magnetic field and temperature dependences of the resistivity and the conductivity tensor components allows us to separate the ballistic and diffusion parts of the correction. It is shown that the ballistic part renormalizes in the main the electron mobility, whereas the diffusion part contributes to the diagonal and does not to the off-diagonal component of the conductivity tensor. We have experimentally found the values of the Fermi-liquid parameters describing the electron-electron contribution to the transport coefficients, which are found in a good agreement with the theoretical results.

cond-mat.dis-nn↗
arXiv2005

Hole-hole interaction in a strained In$_x$Ga$_{1-x}$As two dimensional system

The interaction correction to the conductivity of 2D hole gas in strained GaAs/In$_x$Ga$_{1-x}$As/GaAs quantum well structures was studied. It is shown that the Zeeman splitting, spin relaxation and ballistic contribution should be taking into account for reliable determination of the Fermi-liquid constant $F_0^σ$. The proper consideration of these effects allows us to describe both th temperature and magnetic field dependences of the conductivity and find the value of $F_0^σ$.

cond-mat.dis-nn↗
arXiv2004

Magnetoresistance and dephasing in a two-dimensional electron gas at intermediate conductances

We study, both theoretically and experimentally, the negative magnetoresistance (MR) of a two-dimensional (2D) electron gas in a weak transverse magnetic field $B$. The analysis is carried out in a wide range of zero-$B$ conductances $g$ (measured in units of $e^2/h$), including the range of intermediate conductances, $g\sim 1$. Interpretation of the experimental results obtained for a 2D electron gas in GaAs/In$_x$Ga$_{1-x}$As/GaAs single quantum well structures is based on the theory which takes into account terms of higher orders in $1/g$, stemming from both the interference contribution and the mutual effect of weak localization (WL) and Coulomb interaction. We demonstrate that at intermediate conductances the negative MR is described by the standard WL "digamma-functions" expression, but with a reduced prefactor $α$. We also show that at not very high $g$ the second-loop corrections dominate over the contribution of the interaction in the Cooper channel, and therefore appear to be the main source of the lowering of the prefactor, $α\simeq 1-2/πg$. We further analyze the regime of a "weak insulator", when the zero-$B$ conductance is low $g(B=0)<1$ due to the localization at low $T$, whereas the Drude conductance is high, $g_0>>1.$ In this regime, while the MR still can be fitted by the digamma-functions formula, the experimentally obtained value of the dephasing rate has nothing to do with the true one. The corresponding fitting parameter in the low-$T$ limit is determined by the localization length and may therefore saturate at $T\to 0$, even though the true dephasing rate vanishes.

cond-mat.mes-hall↗
arXiv2003

Nonohmic conductivity as a probe of crossover from diffusion to hopping in two dimensions

We show that the study of conductivity nonlinearity gives a possibility to determine the condition when the diffusion conductivity changes to the hopping one with increasing disorder. It is experimentally shown that the conductivity of single quantum well GaAs/InGaAs/GaAs heterostructures behaves like diffusive one down to value of order $10^{-2}e^2/h$.

cond-mat.dis-nn↗
arXiv2003

Weak antilocalization in quantum wells in tilted magnetic fields

Weak antilocalization is studied in an InGaAs quantum well. Anomalous magnetoresistance is measured and described theoretically in fields perpendicular, tilted and parallel to the quantum well plane. Spin and phase relaxation times are found as functions of temperature and parallel field. It is demonstrated that spin dephasing is due to the Dresselhaus spin-orbit interaction. The values of electron spin splittings and spin relaxation times are found in the wide range of 2D density. Application of in-plane field is shown to destroy weak antilocalization due to competition of Zeeman and microroughness effects. Their relative contributions are separated, and the values of the in-plane electron g-factor and characteristic size of interface imperfections are found.

cond-mat.mes-hall↗
arXiv2003

Transverse negative magnetoresistance of 2D structures in the presence of strong in-plane magnetic field: weak localization as a probe of interface roughness

The interference induced transverse negative magnetoresistance of GaAs/InGaAs/GaAs quantum well heterostructures has been studied in the presence of strong in-plane magnetic field. It is shown that effect of in-plane magnetic field is determined by the interface roughness and strongly depends on the relationship between mean free path, phase breaking length and roughness correlation length. Analysis of the experimental results allows us to estimate parameters of short- and long-range correlated roughness which have been found in a good agreement with atomic force microscopy data obtained for just the same samples.

cond-mat↗