Soft inter-Landau level spin-flip magnetoexciton as a precursor of ferromagnetic instability
We investigate the impact of Coulomb correlations on the low-energy collective excitations in two-dimensional electron systems in the quantum Hall state ν = 2. The collective excitations are studied using inelastic light scattering in the set of MgZnO/ZnO heterostructures with high-mobility two-dimensional electrons. The study focuses on the lowest-energy collective excitations in the paramagnetic state ν = 2, the cyclotron spin-flip magnetoexcitons (CSFMs), which are associated with inter-Landau-level transitions with a simultaneous spin flip. The Coulomb contribution to the CSFM energy is measured independently of the Zeeman term as a function of electron density. It is established that in the range of electron concentrations corresponding to theWigner-Seitz parameter rs ∼ 5–7, the combination of the Coulomb and Zeeman contributions leads to a softening of the CSFM. This softening accompanies spontaneous switching of the spin configuration in the ν = 2 quantum Hall system from paramagnetic to ferromagnetic. Theoretical estimates are given for the correlation energy terms of the CSFM responsible for its softening and a concomitant ferromagnetic transition.
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.
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.
By using superconducting quantum interference device (SQUID) magnetometry, we investigated anisotropic high-field (H less than or similar to 7T) low-temperature (10 K) magnetization response of inhomogeneous nanoisland FeNi films grown by rf sputtering deposition on Sitall (TiO2) glass substrates. In the grown FeNi films, the FeNi layer nominal thickness varied from 0.6 to 2.5 nm, across the percolation transition at the d(c) similar or equal to 1.8 nm. We discovered that, beyond conventional spin-magnetism of Fe21Ni79 permalloy, the extracted out-of-plane magnetization response of the nanoisland FeNi films is not saturated in the range of investigated magnetic fields and exhibits paramagnetic-like behavior. We found that the anomalous out-of-plane magnetization response exhibits an escalating slope with increase in the nominal film thickness from 0.6 to 1.1 nm, however, it decreases with further increase in the film thickness, and then practically vanishes on approaching the FeNi film percolation threshold. At the same time, the in-plane response demonstrates saturation behavior above 1.5-2T, competing with anomalously large diamagnetic-like response, which becomes pronounced at high magnetic fields. It is possible that the supported-metal interaction leads to the creation of a thin charge-transfer (CT) layer and a Schottky barrier at the FeNi film/Sitall (TiO2) interface. Then, in the system with nanoscale circular domains, the observed anomalous paramagnetic-like magnetization response can be associated with a large orbital moment of the localized electrons. In addition, the inhomogeneous nanoisland FeNi films can possess spontaneous ordering of toroidal moments, which can be either of orbital or spin origin. The system with toroidal inhomogeneity can lead to anomalously strong diamagnetic-like response. The observed magnetization response is determined by the interplay between the paramagnetic-and diamagnetic-like contributions.
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.