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ABSTRACT: The results of experimental study of interference induced magnetoconductivity
in narrow quantum well HgTe with the normal energy spectrum are presented.
Analysis is performed with taking into account the conductivity anisotropy. It
is shown that the fitting parameter \tau_\phi corresponding to the phase
relaxation time increases in magnitude with the increasing conductivity
(\sigma) and decreasing temperature following the 1/T law. Such a behavior is
analogous to that observed in usual two-dimensional systems with simple energy
spectrum and corresponds to the inelasticity of electron-electron interaction
as the main mechanism of the phase relaxation. However, it drastically differs
from that observed in the wide HgTe quantum wells with the inverted spectrum,
in which \tau_\phi being obtained by the same way is practically independent of
\sigma. It is presumed that a different structure of the electron
multicomponent wave function for the inverted and normal quantum wells could be
reason for such a discrepancy.
04/2013;
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ABSTRACT: The results of experimental study of the magnetoresistivity, the Hall and
Shubnikov-de Haas effects for the heterostructure with HgTe quantum well of
20.2 nm width are reported. The measurements were performed on the gated
samples over the wide range of electron and hole densities including vicinity
of a charge neutrality point. Analyzing the data we conclude that the energy
spectrum is drastically different from that calculated in framework of
$kP$-model. So, the hole effective mass is equal to approximately $0.2 m_0$ and
practically independent of the quasimomentum ($k$) up to $k^2\gtrsim 0.7\times
10^{12}$ cm$^{-2}$, while the theory predicts negative (electron-like)
effective mass up to $k^2=6\times 10^{12}$ cm$^{-2}$. The experimental
effective mass near k=0, where the hole energy spectrum is electron-like, is
close to $-0.005 m_0$, whereas the theoretical value is about $-0.1 m_0$.
11/2012;
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ABSTRACT: This study is devoted to investigation of the nonlinear behavior of the Hall resistance in low magnetic fields. When investigating
two-dimensional electron gas in single GaAs/In
x
Ga1 − x
As/GaAs quantum wells, it is shown that the anomaly of the Hall effect in disordered systems can be described taking into
account the second-order quantum corrections to conductivity.
Semiconductors 04/2012; 44(11):1430-1434. · 0.63 Impact Factor
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ABSTRACT: The results of experimental study of the magnetoconductivity of 2D electron
gas caused by suppression of the interference quantum correction in HgTe single
quantum well heterostructure with the inverted energy spectrum are presented.
It is shown that only the antilocalization magnetoconductivity is observed at
the relatively high conductivity $\sigma>(20-30)G_0$, where $G_0=
e^2/2\pi^2\hbar$. The antilocalization correction demonstrates a crossover from
$0.5\ln{(\tau_\phi/\tau)}$ to $1.0\ln{(\tau_\phi/\tau)}$ behavior with the
increasing conductivity or decreasing temperature (here $\tau_\phi$ and $\tau$
are the phase relaxation and transport relaxation times, respectively). It is
interpreted as a result of crossover to the regime when the two chiral branches
of the electron energy spectrum contribute to the weak antilocalization
independently. At lower conductivity $\sigma<(20-30)G_0$, the
magnetoconductivity behaves itself analogously to that in usual 2D systems with
the fast spin relaxation: being negative in low magnetic field it becomes
positive in higher one. We have found that the temperature dependences of the
fitting parameter $\tau_\phi$ corresponding to the phase relaxation time
demonstrate reasonable behavior, close to 1/T, over the whole conductivity
range from $5G_0$ up to $130G_0$. However, the $\tau_\phi$ value remains
practically independent of the conductivity in distinction to the conventional
2D systems with the simple energy spectrum, in which $\tau_\phi$ is enhanced
with the conductivity.
02/2012;
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ABSTRACT: The electron-electron interaction quantum correction to the conductivity of
the gated single quantum well InP/In$_{0.53}$Ga$_{0.47}$As heterostructures is
investigated experimentally. The analysis of the temperature and magnetic field
dependences of the conductivity tensor allows us to obtain reliably the
diffusion part of the interaction correction for different values of spin
relaxation rate, $1/\tau_s$. The surprising result is that the spin relaxation
processes do not suppress the interaction correction in the triplet channel
and, thus, do not enhance the correction in magnitude contrary to theoretical
expectations even in the case of relatively fast spin relaxation,
$1/T\tau_s\simeq (20-25)\gg 1$.
11/2011;
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ABSTRACT: The nonohmic conductivity of two-dimensional hole gas (2DHG) in single GaAsIn0.2Ga0.8AsGaAs quantum-well structures within the temperature range of 1.4–4.2 K, the carrier’s densities p=(1.5-8)×1015m-2 and a wide range of conductivities (10-4–100)G0 (G0=e2/π h) was investigated. It was shown that at conductivity σ>G0 the energy relaxation rate P(Th,TL) 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 0.01G0<σ<G0 energy the relaxation rate significantly deviates down from the theoretical value. The analysis of DP/dσ at different lattice temperature TL shows that this deviation does not result from crossover to the hopping conductivity, which occurs at σ<10-2, but from the Pippard ineffectiveness.
Phys. Rev. B. 02/2011; 83(8).
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ABSTRACT: The electron-electron interaction quantum correction to the conductivity of
the gated double well Al$_x$Ga$_{1-x}$As/GaAs structures is investigated
experimentally. The analysis of the temperature and magnetic field dependences
of the conductivity tensor allows us to obtain reliably the diffusion part of
the interaction correction for the regimes when the structure is balanced and
when only one quantum well is occupied. The surprising result is that the
interaction correction does not reveal resonant behavior; it is practically the
same for both regimes.
01/2011;
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ABSTRACT: 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 $(10^{-4}-100)G_0$ ($G_0=e^2/\pi\,h$) was investigated. It was shown that at conductivity $\sigma>G_0$ 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 $0.01G_0<\sigma<G_0$ energy the relaxation rate significantly deviates down from the theoretical value. The analysis of $\frac{dP}{d\sigma}$ at different lattice temperature $T_L$ shows that this deviation does not result from crossover to the hopping conductivity, which occurs at $\sigma<10^{-2}$, but from the Pippard ineffectiveness. Comment: 13 pages, 6 figures
10/2010;
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ABSTRACT: 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. Comment: 5 pages, 5 figures
09/2010;
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ABSTRACT: 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 $\tau_{12}$ and the electron dephasing time $\tau_\phi$. It has been obtained that $\tau_{12}^{-1}$ 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 $\tau_\phi$ value in the one well does not depend on the occupation of the other one. Comment: 7 pages, 8 figures
07/2010;
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ABSTRACT: 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. Comment: 7 pages, 7 figures
04/2010;
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Physica E Low-dimensional Systems and Nanostructures 01/2010; 42:960. · 1.53 Impact Factor
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ABSTRACT: 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, $\sigma\simeq(1-150) G_0$, where $G_0=e^2/(2\pi^2\hbar)$. 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, $\sigma \gtrsim 15 G_0$. 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.
04/2009;
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ABSTRACT: We report experimental observations of a novel magnetoresistance (MR)
behavior of two-dimensional electron systems in perpendicular magnetic field in
the ballistic regime, for k_BT\tau/\hbar>1. The MR grows with field and
exhibits a maximum at fields B>1/\mu, where \mu is the electron mobility. As
temperature increases the magnitude of the maximum grows and its position moves
to higher fields. This effect is universal: it is observed in various Si- and
GaAs- based two-dimensional electron systems. We compared our data with recent
theory based on the Kohn anomaly modification in magnetic field, and found
qualitative similarities and discrepancies.
02/2009;
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ABSTRACT: 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.
06/2008;
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ABSTRACT: The temperature dependence of the conductivity of the two-dimensional hole gas in an asymmetric GaAs/In
x
Ga1 − x
As/GaAs quantum well has been investigated. It is shown that fast spin relaxation leads to metallic-like behavior of the temperature
dependence of the conductivity.
Bulletin of the Russian Academy of Sciences Physics 01/2008; 72(2):219-222.
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ABSTRACT: 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 $\alpha_i<1$ in the conventional expression for the interaction correction.
06/2007;
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ABSTRACT: Temperature and magnetic-field dependences of the conductivity in heavily doped, strongly disordered two-dimensional quantum well structures GaAs∕InxGa1−xAs∕GaAs are investigated within wide conductivity and temperature ranges. The role of the interference in electron transport is studied in the regimes where the phase breaking length Lϕ crosses over the localization length ξ∼l exp(πkFl∕2) with decreasing temperature, where kF and l are the Fermi quasimomentum and mean free path, respectively. It is shown that all the experimental data can be understood within a simple model of the conductivity over delocalized states. This model differs from the conventional model of weak localization developed for kFl⪢1 and Lϕ⪡ξ in one respect: the value of the quantum interference contribution to the conductivity is restricted not only by the phase breaking length Lϕ but also by the localization length ξ. In this approach, it is the quantity (τϕ*)−1=τϕ−1+τξ−1, rather than τϕ−1 [where τϕ∝T−1 is the dephasing time and τξ∼τ exp(πkFl)], that governs temperature and magnetic-field dependences of the conductivity over the wide range of temperature and disorder strength down to the conductivity of order 10−2e2∕h.
Phys. Rev. B. 06/2007; 75(23).
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ABSTRACT: 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$<T<4$ K, it is due to the interaction quantum correction. Finally, at $T>4-6$ K, the metallic-like behavior is determined by the phonon scattering.
03/2007;
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ABSTRACT: 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 $L_\phi$ crosses over the localization length $\xi\sim l\exp{(\pi k_Fl/2)}$ 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 $L_\phi\ll\xi$ by one point: the value of the quantum interference contribution to the conductivity is restricted not only by the phase breaking length $L_\phi$ but by the localization length $\xi$ as well. We show that just the quantity $(\tau_\phi^\ast)^{-1}=\tau_\phi^{-1}+\tau_\xi^{-1}$ rather than $\tau_\phi^{-1}$, where $\tau_\phi\propto T^{-1}$ is the dephasing time and $\tau_\xi\sim\tau\exp(\pi k_F l)$, 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 $10^{-2} e^2/h$.
07/2006;
