Probing Electron Interactions in a Two-Dimensional System by Quantum Magneto-Oscillations
We have experimentally studied the renormalized effective mass m* and Dingle temperature TD in two spin subbands with essentially different electron populations. Firstly, we found that the product m*T_D that determines the damping of quantum oscillations, to the first approximation, is the same in the majority and minority subbands even at a spin polarization degree as high as 66%. This result confirms the theoretical predictions that the interaction takes place at high energies ~EF rather than within a narrow strip of energies EF ± kBT . Secondly, to the next approximation, we revealed a difference in the damping factor of the two spin subbands, which causes skewness of the oscillation line shape. In the absence of the in-plane magnetic field , the damping factor m*T_D is systematically smaller in the spin-majority subband. The difference, quantified with the skew
factor γ = (TD↓ − TD↑)/2T_D0 can be as large as 20%. The skew factor tends to decrease as B or temperature grow, or B⊥ decreases; for low electron densities and high in-plane fields, the skew factor even changes sign. Finally, we compared the temperature and magnetic field dependencies of the magneto-oscillation amplitude with predictions of the interaction correction theory, and found, besides some qualitative similarities, several quantitative and qualitative differences. To explain qualitatively our results, we suggested an empirical model that assumes the existence of easily magnetized triplet scatterers on the Si/SiO2 interface.
Strongly interacting two-dimensional (2D) carrier system has a tendency to spontaneous spin magnetization and mass divergence. Numerous experiments aimed to reveal these instabilities were not entirely convincing. In particular, spin susceptibility of itinerant electrons, determined from quantum oscillations, remains finite at the critical density of the 2D metal-insulator transition (MIT), n = nc. In contrast, the susceptibility and effective mass determined from high field magnetotransport were reported to diverge. Later, it became clear that as interactions grow, the homogeneous 2D Fermi liquid breaks into a two phase state which hampers interpretation of the experimental data. The thermodynamic magnetization measurements have revealed spontaneous formation of the spin-polarized collective electron droplets (“nanomagnets”) in the correlated 2D Fermi liquid, while the spin susceptibility of itinerant electrons in the surrounding 2D “Fermi sea” remains finite. Here, we report how the non Fermi-liquid two-phase state (dilute ferromagnet) reveals itself in magnetotransport and zero field transport. We found in the correlated 2D system a novel energy scale T∗<TF. At T≈T∗ the in-plane field magnetotransport and zero field transport exhibit features. Finally, in thermodynamic magnetization, the spin susceptibility per electron, ∂χ/∂n changes sign at T≈T∗. All three notable temperatures are close to each other, behave critically, <span data-mathml="∝(Н−П−С)∝(Н−П−С); we associate, therefore, T∗ with a novel energy scale caused by interactions in the two-phase 2DE system.
We develop a systematic strong coupling approach for studying an extended t-V model with interactions of a finite range. Our technique is not based on the Bethe ansatz and is applicable to both integrable and non-integrable models. We illustrate our technique by presenting analytic results for the ground state energy (up to order 7 in t/V), the current density and density-density correlations for integrable and non-integrable models with commensurate filling factors. We further present preliminary numerical results for incommensurate non- integrable models.
We study the thermodynamics of the three-dimensional Hubbard model at half filling on approach to the Néel transition by means of large-scale unbiased diagrammatic determinant Monte Carlo simulations. We obtain the transition temperature in the strongly correlated regime, as well as the temperature dependence of the energy, entropy, double occupancy, and nearest-neighbor spin correlation function. Our results improve the accuracy of previous unbiased studies and present accurate benchmarks in the ongoing effort to realize the antiferromagnetic state of matter with ultracold atoms in optical lattices.
The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.
This volume presents new results in the study and optimization of information transmission models in telecommunication networks using different approaches, mainly based on theiries of queueing systems and queueing networks .
The paper provides a number of proposed draft operational guidelines for technology measurement and includes a number of tentative technology definitions to be used for statistical purposes, principles for identification and classification of potentially growing technology areas, suggestions on the survey strategies and indicators. These are the key components of an internationally harmonized framework for collecting and interpreting technology data that would need to be further developed through a broader consultation process. A summary of definitions of technology already available in OECD manuals and the stocktaking results are provided in the Annex section.