Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userTwo sub-band conductivity of Si quantum well
222
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report on two sub-band transport in double gate SiO$_2$-Si-SiO$_2$ quantum well with 14 nm thick Si layer at 270 mK. At symmetric well potential the experimental sub-band spacing changes monotonically from 2.3 to 0.3 meV when the total density is adjusted by gate voltages between $sim 0.7times 10^{16}$ $-3.0times 10^{16}$ m$^{-2}$. The conductivity is mapped in large gate bias window and it shows strong non-monotonic features. At symmetric well potential and high density these features are addressed to sub-band wave function delocalization in the quantization direction and to different disorder of the top and bottom interfaces of the Si well. Close to bi-layer/second sub-band threshold the non-monotonic behavior is interpreted to arise from scattering from localized band tail electrons.
rate research
Read More
In one-dimensional electronic systems with strong repulsive interactions, charge excitations propagate much faster than spin excitations. Such systems therefore have an intermediate temperature range [termed the spin-incoherent Luttinger liquid (SILL) regime] where charge excitations are cold (i.e., have low entropy) whereas spin excitations are hot. We explore the effects of charge-sector disorder in the SILL regime in the absence of external sources of equilibration. We argue that the disorder localizes all charge-sector excitations; however, spin excitations are protected against full localization, and act as a heat bath facilitating charge and energy transport on asymptotically long timescales. The charge, spin, and energy conductivities are widely separated from one another. The dominant carriers of energy are neither charge nor spin excitations, but neutral phonon modes, which undergo an unconventional form of hopping transport that we discuss. We comment on the applicability of these ideas to experiments and numerical simulations.
Magnetotransport measurements in combination with molecular dynamics (MD) simulations on two-dimensional disordered Lorentz gases in the classical regime are reported. In quantitative agreement between experiment and simulation, the magnetoconductivity displays a pronounced peak as a function of perpendicular magnetic field $B$ which cannot be explained in the framework of existing kinetic theories. We show that this peak is linked to the onset of a directed motion of the electrons along the contour of the disordered obstacle matrix when the cyclotron radius becomes smaller than the size of the obstacles. This directed motion leads to transient superdiffusive motion and strong scaling corrections in the vicinity of the insulator-to-conductor transitions of the Lorentz gas.
We have measured the conductivity of high-mobility (001) Si metal-oxide-semiconductor field effect transistors (MOSFETs) over wide ranges of electron densities n=(1.8-15)x10^11cm^2, temperatures T=30mK-4.2K, and in-plane magnetic fields B=0-5T. The experimental data have been analyzed using the theory of interaction effects in the conductivity of disordered 2D systems. The parameters essential for comparison with the theory, such as the intervalley scattering time and valley splitting, have been measured or evaluated in independent experiments. The observed behavior of the conductivity, including its quasi-linear increase with decreasing T down to ~0.4K and its downturn at lower temperatures, is in agreement with the theory. The values of the Fermi- liquid parameter obtained from the comparison agree with the corresponding values extracted from the analysis of Shubnikov-de Haas oscillations based on the theory of magnetooscillations in interacting 2D systems.
We discuss quantum propagation of dipole excitations in two dimensions. This problem differs from the conventional Anderson localization due to existence of long range hops. We found that the critical wavefunctions of the dipoles always exist which manifest themselves by a scale independent diffusion constant. If the system is T-invariant the states are critical for all values of the parameters. Otherwise, there can be a metal-insulator transition between this ordinary diffusion and the Levy-flights (the diffusion constant logarithmically increasing with the scale). These results follow from the two-loop analysis of the modified non-linear supermatrix $sigma$-model.
We report experimental studies of conductance and magnetoconductance of GaAs/AlGaAs quantum well structures where both wells and barriers are doped by acceptor impurity Be. Temperature dependence of conductance demonstrate a non-monotonic behavior at temperatures around 100 K. At small temperatures (less than 10 K) we observed strong negative magnetoresistance at moderate magnetic field which crossed over to positive magnetoresistance at very strong magnetic fields and was completely suppressed with an increase of temperature. We ascribe these unusual features to effects of temperature and magnetic field on a degree of disorder. The temperature dependent disorder is related to charge redistribution between different localized states with an increase of temperature. The magnetic field dependent disorder is also related by charge redistribution between different centers, however in this case an important role is played by the doubly occupied states of the upper Hubbard band, their occupation being sensitive to magnetic field due to on-site spin correlations. The detailed theoretical model is present.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
