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Register a new userInteraction Effects in Conductivity of a Two-Valley Electron System in High-Mobility Si Inversion Layers
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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.
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We report the observation of an electron gas in a SiGe/Si/SiGe quantum well with maximum mobility up to 240 m^2/Vs, which is noticeably higher than previously reported results in silicon-based structures. Using SiO, rather than Al_2O_3, as an insulator, we obtain strongly reduced threshold voltages close to zero. In addition to the predominantly small-angle scattering well known in the high-mobility heterostructures, the observed linear temperature dependence of the conductivity reveals the presence of a short-range random potential.
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.
We report direct measurements of the valley susceptibility, the change of valley population in response to applied symmetry-breaking strain, in an AlAs two-dimensional electron system. As the two-dimensional density is reduced, the valley susceptibility dramatically increases relative to its band value, reflecting the systems strong electron-electron interaction. The increase has a remarkable resemblance to the enhancement of the spin susceptibility and establishes the analogy between the spin and valley degrees of freedom.
We show that the temperature dependence of conductivity of high mobility organic crystals Pentacene and Rubrene can be quantitatively described in the framework of the model where carriers are scattered by quenched local impurities and interact with phonons by Su-Schrieffer-Hegger (SSH) coupling. Within this model, we present approximation free results for mobility and optical conductivity obtained by world line Monte Carlo, which we generalize to the case of coupling both to phonons and impurities. We find fingerprints of carrier dynamics in these compounds which differ from conventional metals and show that the dynamics of carriers can be described as a superposition of a Drude term representing diffusive mobile particles and a Lorentz term associated with dynamics of localized charges.
Mean-field theory of non-interacting disordered electron systems is widely and successfully used to describe equilibrium properties of alloys in the whole range of disorder strengths. It, however, fails to take into account effects of quantum coherence and localizing back-scattering effects when applied to transport phenomena. We present an approximate scheme extending the mean-field theory for one-electron properties in that it offers a formula for the two-particle vertex and the electrical conductivity non-perturbatively including the leading-order vertex corrections in a way that the approximation remains consistent and the conductivity non-negative in all disorder regimes.
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