21 research outputs found
Boundary resistance in magnetic multilayers
Quasiclassical boundary conditions for electrochemical potentials at the
interface between diffusive ferromagnetic and non-magnetic metals are derived
for the first time. An expression for the boundary resistance accurately
accounts for the momentum conservation law as well as essential gradients of
the chemical potentials. Conditions are established at which spin-asymmetry of
the boundary resistance has positive or negative sign. Dependence of the spin
asymmetry and the absolute value of the boundary resistance on the exchange
splitting of the conduction band opens up new possibility to estimate spin
polarization of the conduction band of ferromagnetic metals. Consistency of the
theory is checked on existing experimental data.Comment: 8 pages, 3 figures, designed using IOPART styl
Surface potential at a ferroelectric grain due to asymmetric screening of depolarization fields
Nonlinear screening of electric depolarization fields, generated by a stripe
domain structure in a ferroelectric grain of a polycrystalline material, is
studied within a semiconductor model of ferroelectrics. It is shown that the
maximum strength of local depolarization fields is rather determined by the
electronic band gap than by the spontaneous polarization magnitude.
Furthermore, field screening due to electronic band bending and due to presence
of intrinsic defects leads to asymmetric space charge regions near the grain
boundary, which produce an effective dipole layer at the surface of the grain.
This results in the formation of a potential difference between the grain
surface and its interior of the order of 1 V, which can be of either sign
depending on defect transition levels and concentrations. Exemplary acceptor
doping of BaTiO3 is shown to allow tuning of the said surface potential in the
region between 0.1 and 1.3 V.Comment: 14 pages, 11 figures, submitted to J. Appl. Phy
Electron-phonon interaction via Pekar mechanism in nanostructures
We consider an electron-acoustic phonon coupling mechanism associated with
the dependence of crystal dielectric permittivity on the strain (the so-called
Pekar mechanism) in nanostructures characterized by strong confining electric
fields. The efficiency of Pekar coupling is a function of both the absolute
value and the spatial distribution of the electric field. It is demonstrated
that this mechanism exhibits a phonon wavevector dependence similar to that of
piezoelectricity and must be taken into account for electron transport
calculations in an extended field distribution. In particular, we analyze the
role of Pekar coupling in energy relaxation in silicon inversion layers.
Comparison with the recent experimental results is provided to illustrate its
potential significance
Bloch's theory in periodic structures with Rashba's spin-orbit interaction
We consider a two-dimensional electron gas with Rashba's spin-orbit
interaction and two in-plane potentials superimposed along directions
perpendicular to each other. The first of these potentials is assumed to be a
general periodic potential while the second one is totally arbitrary. A general
form for Bloch's amplitude is found and an eigen-value problem for the band
structure of the system is derived. We apply the general result to the two
particular cases in which either the second potential represents a harmonic
in-plane confinement or it is zero. We find that for a harmonic confinement
regions of the Brillouin zone with high polarizations are associated with the
ones of large group velocity.Comment: 6 pages, 5 figure
Essential spectra and exponential estimates of eigenfunctions of lattice operators of quantum mechanics
This paper is devoted to estimates of the exponential decay of eigenfunctions
of difference operators on the lattice Z^n which are discrete analogs of the
Schr\"{o}dinger, Dirac and square-root Klein-Gordon operators. Our
investigation of the essential spectra and the exponential decay of
eigenfunctions of the discrete spectra is based on the calculus of so-called
pseudodifference operators (i.e., pseudodifferential operators on the group
Z^n) with analytic symbols and on the limit operators method. We obtain a
description of the location of the essential spectra and estimates of the
eigenfunctions of the discrete spectra of the main lattice operators of quantum
mechanics, namely: matrix Schr\"{o}dinger operators on Z^n, Dirac operators on
Z^3, and square root Klein-Gordon operators on Z^n
Nature of the quantum critical point as disclosed by extraordinary behavior of magnetotransport and the Lorentz number in the heavy-fermion metal YbRh2Si2
Physicists are engaged in vigorous debate on the nature of the quantum
critical points (QCP) governing the low-temperature properties of heavy-fermion
(HF) metals. Recent experimental observations of the much-studied compound
YbRh2Si2 in the regime of vanishing temperature incisively probe the nature of
its magnetic-field-tuned QCP. The jumps revealed both in the residual
resistivity rho_0 and the Hall resistivity R_H, along with violation of the
Wiedemann-Franz law, provide vital clues to the origin of such non-Fermi-liquid
behavior. The empirical facts point unambiguously to association of the
observed QCP with a fermion-condensation phase transition. Based on this
insight, the resistivities rho_0 and R_H are predicted to show jumps at the
crossing of the QCP produced by application of a magnetic field, with attendant
violation of the Wiedemann-Franz law. It is further demonstrated that
experimentally identifiable multiple energy scales are related to the scaling
behavior of the effective mass of the quasiparticles responsible for the
low-temperature properties of such HF metals.Comment: 7 pages, 4 figures, revised and accepted by JETP Let