39 research outputs found
Spectroscopy of phonons and spin torques in magnetic point contacts
Phonon spectroscopy is used to investigate the mechanism of current-induced
spin torques in nonmagnetic/ferromagnetic (N/F) point contacts. Magnetization
excitations observed in the magneto-conductance of the point contacts are
pronounced for diffusive and thermal contacts, where the electrons experience
significant scattering in the contact region. We find no magnetic excitations
in highly ballistic contacts. Our results show that impurity scattering at the
N/F interface is the origin of the new single-interface spin torque effect.Comment: 4 pages, 5 figs., accepted for publication in PR
Non-Equilibrium Magnetization in a Ballistic Quantum Dot
We show that Aharonov-Bohm (AB) oscillations in the magnetic moment of an
integrable ballistic quantum dot can be destroyed by a time dependent magnetic
flux. The effect is due to a nonequilibrium population of perfectly coherent
electronic states. For real ballistic systems the equilibrization process,
which involves a special type of inelastic electron backscattering, can be so
ineffective, that AB oscillations are suppressed when the flux varies with
frequency 10-10 s. The effect can be used to
measure relaxation times for inelastic backscattering.Comment: 11 pages LaTeX v3.14 with RevTeX v3.0, 3 post script figures
available on request, APR 93-X2
Neutron charge radius and the Dirac equation
We consider the Dirac equation for a finite-size neutron in an external
electric field. We explicitly incorporate Dirac-Pauli form factors into the
Dirac equation. After a non-relativistic reduction, the Darwin-Foldy term is
cancelled by a contribution from the Dirac form factor, so that the only
coefficient of the external field charge density is , i. e. the
root mean square radius associated with the electric Sachs form factor . Our
result is similar to a recent result of Isgur, and reconciles two apparently
conflicting viewpoints about the use of the Dirac equation for the description
of nucleons.Comment: 7 pages, no figures, to appear in Physical Review
Point-contact spectroscopy of the antiferromagnetic superconductor HoNi2B2C in the normal and superconducting state
Point-contact (PC) spectroscopy measurements on antiferromagnetic (AF)
(T_N=5.2K) HoNi2B2C single crystals in the normal and two different
superconducting (SC) states (T_c=8.5K and T_c^*=5.6K<T_c, with 2\Delta/kT_c^*=3.9. The strong coupling
Eliashberg analysis of the low-temperature SC phase with T_c^*=5.6K =T_N,
coexisting with the commensurate AF structure, suggests a sizable value of the
EPI constant \lambda_s=0.93. We also provide strong support for the recently
proposed by us ''Fermi surface (FS) separation'' scenario for the coexistence
of magnetism and superconductivity in magnetic borocarbides, namely, that the
superconductivity in the commensurate AF phase survives at a special (nearly
isotropic) FS sheet without an admixture of Ho 5d states. Above T_c^* the SC
features in the PC characteristics are strongly suppressed pointing to a
specific weakened SC state between T_c* and T_c.Comment: 11 pages, 8 figs, to be published in PRB, Vol.75, Iss.2
Noise in a Quantum Point Contact due to a Fluctuating Impurity Configuration
We propose a theoretical model for the low-frequency noise observed in a
quantum point contact (QPC) electrostatically defined in the 2D electron gas at
a GaAs-AlGaAs interface. In such contacts electron scattering by soft impurity-
or boundary potentials coherently splits an incoming wave function between
different transverse modes. Interference between these modes have been
suggested to explain observed non-linearities in the QPC-conductance. In this
study we invoke the same mechanism and the time-dependent current due to soft
dynamical impurity scattering in order to analyze the low-frequency
(telegraph-like) noise which has been observed along with a nonlinear
conductance. For the simplified case of a channel with two extended (current
carrying) modes, a simple analytical formula for the noise intensity is
derived. Generally we have found qualitative similarities between the noise and
the square of the transconductance. Nevertheless, incidentally there may be
situations when noise is suppressed but transconductance enhanced.Comment: 9 revte
Chiral spin resonance and spin-Hall conductivity in the presence of the electron-electron interactions
We discuss the electron spin resonance in two-dimensional electron gas at
zero external magnetic field. This spin-resonance is due to the transitions
between the electron states, which are split by the spin-orbit (SO)
interaction, and is termed as the chiral spin resonance (CSR). It can be
excited by the in-plane component of the electric field of microwave radiation.
We show that there exists an inherent relationship between the spin-Hall
conductivity and the CSR in a system with the SO interaction. Since in the
presence of the SO interaction spin is not conserved, the electron-electron
interaction renormalizes the spin-Hall conductivity as well as the frequency of
the CSR. The effects of the electron interaction in systems with the SO
interaction are analyzed both phenomenologically and microscopically.Comment: 14 page
Steam turbines produced by the Ural Turbine Works for combined-cycle plants
The most interesting and innovative solutions adopted in the projects of steam turbines for combined-cycle plants with capacities from 115 to 900 MW are pointed out. The development of some ideas and components from the first projects to subsequent ones is shown. © 2013 Pleiades Publishing, Ltd
Joule Heating and Current-Induced Instabilities in Magnetic Nanocontacts
We consider the electrical current through a magnetic point contact in the
limit of a strong inelastic scattering of electrons. In this limit local Joule
heating of the contact region plays a decisive role in determining the
transport properties of the point contact. We show that if an applied constant
bias voltage exceeds a critical value, the stationary state of the system is
unstable, and that periodic, non-harmonic oscillations in time of both the
electrical current through the contact and the local temperature in the contact
region develop spontaneously. Our estimations show that the necessary
experimental conditions for observing such oscillations with characteristic
frequencies in the range Hz can easily be met. We also show a
possibility to manipulate upon the magnetization direction of a magnetic grain
coupled through a point contact to a bulk ferromagnetic by exciting the
above-mentioned thermal-electric oscillations.Comment: 9 pages, 6 figures, submitted to Physical Review
Charge and Spin Effects in Mesoscopic Josephson Junctions
We consider the charge and spin effects in low dimensional superconducting
weak links. The first part of the review deals with the effects of
electron-electron interaction in Superconductor/Luttinger liquid/Superconductor
junctions. The experimental realization of this mesoscopic hybrid system can be
the individual single wall carbon nanotube that bridges the gap between two
bulk superconductors. The dc Josephson current through a Luttinger liquid in
the limits of perfectly and poorly transmitting junctions is evaluated. The
relationship between the Josephson effect in a long SNS junction and the
Casimir effect is discussed. In the second part of the paper we review the
recent results concerning the influence of the Zeeman and Rashba interactions
on the thermodynamical properties of ballistic S/QW/S junction fabricated in
two dimensional electron gas. It is shown that in magnetically controlled
junction there are conditions for resonant Cooper pair transition which results
in giant supercurrent through a tunnel junction and a giant magnetic response
of a multichannel SNS junction. The supercurrent induced by the joint action of
the Zeeman and Rashba interactions in 1D quantum wires connected to bulk
superconductors is predicted.Comment: 36 pages, 8 figures; minor changes in reference