118 research outputs found
Temperature Dependence of Microwave Photoresistance in 2D Electron Systems
We report on the temperature dependence of microwave-induced resistance
oscillations in high-mobility two-dimensional electron systems. We find that
the oscillation amplitude decays exponentially with increasing temperature, as
, where scales with the inverse magnetic field.
This observation indicates that the temperature dependence originates primarily
from the modification of the single particle lifetime, which we attribute to
electron-electron interaction effects.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
A Noncommutative Space Approach to Confined Dirac Fermions in Graphene
A generalized algebra of noncommutative coordinates and momenta embracing
non-Abelian gauge fields is proposed. Through a two-dimensional realization of
this algebra for a gauge field including electromagnetic vector potential and
two spin-orbit-like coupling terms, a Dirac-like Hamiltonian in noncommutative
coordinates is introduced. We established the corresponding energy spectrum and
from that we derived the relation between the energy level quantum number and
the magnetic field at the maxima of Shubnikov-de Haas oscillations. By tuning
the non-commutativity parameter \theta in terms of the values of magnetic field
at the maxima of Shubnikov-de Haas oscillations we accomplished the
experimentally observed Landau plot of the peaks for graphene. Accepting that
the experimentally observed behavior is due to the confinement of carriers, we
conclude that our method of introducing noncommutative coordinates provides
another formulation of the confined massless Dirac fermions in graphene.Comment: 14 pages, 1 figure, paper extended, new references added. Version to
appear in JM
Microwave Photoresistance in dc-driven 2D Systems at Cyclotron Resonance Subharmonics
We study microwave photoresistivity oscillations in a high mobility
two-dimensional electron system subject to strong dc electric fields. We find
that near the second subharmonic of the cyclotron resonance the frequency of
the resistivity oscillations with dc electric field is twice the frequency of
the oscillations at the cyclotron resonance, its harmonics, or in the absence
of microwave radiation. This observation is discussed in terms of the
microwave-induced sidebands in the density of states and the interplay between
different scattering processes in the separated Landau level regime.Comment: 4 pages, 4 figure
Spin-polarized supercurrents for spintronics: a review of current progress
During the past 15 years a new field has emerged, which combines
superconductivity and spintronics, with the goal to pave a way for new types of
devices for applications combining the virtues of both by offering the
possibility of long-range spin-polarized supercurrents. Such supercurrents
constitute a fruitful basis for the study of fundamental physics as they
combine macroscopic quantum coherence with microscopic exchange interactions,
spin selectivity, and spin transport. This report follows recent developments
in the controlled creation of long-range equal-spin triplet supercurrents in
ferromagnets and its contribution to spintronics. The mutual proximity-induced
modification of order in superconductor-ferromagnet hybrid structures
introduces in a natural way such evasive phenomena as triplet
superconductivity, odd-frequency pairing, Fulde-Ferrell-Larkin-Ovchinnikov
pairing, long-range equal-spin supercurrents, -Josephson junctions, as
well as long-range magnetic proximity effects. All these effects were rather
exotic before 2000, when improvements in nanofabrication and materials control
allowed for a new quality of hybrid structures. Guided by pioneering
theoretical studies, experimental progress evolved rapidly, and since 2010
triplet supercurrents are routinely produced and observed. We have entered a
new stage of studying new phases of matter previously out of our reach, and of
merging the hitherto disparate fields of superconductivity and spintronics to a
new research direction: super-spintronics.Comment: 95 pages, 23 Figures; published version with minor typos corrected
and few references adde
Statistical Mechanics and the Physics of the Many-Particle Model Systems
The development of methods of quantum statistical mechanics is considered in
light of their applications to quantum solid-state theory. We discuss
fundamental problems of the physics of magnetic materials and the methods of
the quantum theory of magnetism, including the method of two-time temperature
Green's functions, which is widely used in various physical problems of
many-particle systems with interaction. Quantum cooperative effects and
quasiparticle dynamics in the basic microscopic models of quantum theory of
magnetism: the Heisenberg model, the Hubbard model, the Anderson Model, and the
spin-fermion model are considered in the framework of novel
self-consistent-field approximation. We present a comparative analysis of these
models; in particular, we compare their applicability for description of
complex magnetic materials. The concepts of broken symmetry, quantum
protectorate, and quasiaverages are analyzed in the context of quantum theory
of magnetism and theory of superconductivity. The notion of broken symmetry is
presented within the nonequilibrium statistical operator approach developed by
D.N. Zubarev. In the framework of the latter approach we discuss the derivation
of kinetic equations for a system in a thermal bath. Finally, the results of
investigation of the dynamic behavior of a particle in an environment, taking
into account dissipative effects, are presented.Comment: 77 pages, 1 figure, Refs.37
METHODICAL APPROACH TO THE EVALUATION OF INVESTMENT PROJECTS IN OIL PRODUCTION IN CONDITIONS OF UNCERTAINTY AND RISKS
Development of oilfield is a long term capital-intensive investment project, which is characterized by incomplete and inaccurate information about conditions of its realization. Efficiency evaluation of license area development is impossible without accounting uncertainty associated with oil production. The article analyzes the current state of the Russian oil industry, highlights the main risks affecting the activities of oil companies. Classification of risks in the qualitative and quantitative characteristics is suggested. Methods of economic efficiency evaluation of investments in oil field development in new production regions are considered, the expediency of the fuzzy set theory application is shown. The task of expert systems building for efficiency evaluation of oil field development in terms of uncertainty in risks by investor is actualized. Scheme of an expert system for efficiency evaluation of oil field development using elements of theory of fuzzy sets is proposed
Broken time reversal of light interaction with planar chiral nanostructures
We report unambiguous experimental evidence of broken time-reversal symmetry for the interaction of light with an artificial nonmagnetic material. Polarized color images of planar chiral gold-on-silicon nanostructures consisting of arrays of gammadions show intriguing and unusual symmetry: structures, which are geometrically mirror images, lose their mirror symmetry in polarized light. The symmetry of images can be described only in terms of antisymmetry (black-and-white symmetry) appropriate to a time-odd process. The effect results from a transverse chiral nonlocal electromagnetic response of the structure and has some striking resemblance with the expected features of light scattering on anyon matter
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