arXiv subjects

V. L. Gurevich

Publications and source records attributed to V. L. Gurevich.

At least 19 recordsLinked to original sources

arXiv2015

Comments on the quantum correlation and entanglement

In recent decades it was established that the quantum measurements of physical quantities in space-time points divided by space-like intervals may be correlated. Though such correlation follows from the formulas of quantum mechanics its physics so far remains unclear and there is a number of different and rather contradictory interpretations. They concern particularly the so-called Einstein-Podolsky-Rosen paradox where the momentary action at a distance together with non-local entangled states is used for the interpretation. We assume that the quantum theory can be formulated as local and look for the consequences of this assumption. Accordingly we try to explain the correlation phenomena in a local way looking for the origin of correlation. To exclude a presupposed correlation of participating quantum particles we consider two independent particle sources and two detectors that are independent as well. We show that the origin of the correlation is the feature that the occupation number of a particle (and other its measurable quantities) is formed by a pair of complex conjugated wave functions with in general arbitrary phases. We consider this point as crucial as it provides interpretation of the observed correlation phenomena that may otherwise look puzzling. We briefly discuss a special type of noise that is typical for the quantum correlation phenomena.

quant-ph↗

arXiv2015

Drag of ballistic electrons by an ion beam

Drag of electrons of 1D ballistic nanowire by a nearby 1D beam of ions is considered. We assume that the ion beam is represented by an ensemble of heavy ions of the same velocity $\bf V$. The ratio of the drag current to primary current carried by the ion beam is calculated. The drag current appears to be a nonmonotonic function of velocity $V$, it has maxima for $V$ near $v_{nF}/2$ where $n$ is the number of electron miniband (channel) and $v_{nF}$ is the corresponding Fermi velocity. This means that the ion beam drag can be applied for ballistic nanostructure spectroscopy.

cond-mat.mes-hall↗

arXiv2011

On the temperature dependence of ballistic Coulomb drag in nanowires

We have investigated within the theory of Fermi liquid dependence of Coulomb drag current in a passive quantum wire on the applied voltage $V$ across an active wire and on the temperature $T$ for any values of $eV/k_BT$. We assume that the bottoms of the 1D minibands in both wires almost coincide with the Fermi level. We come to conclusions that 1) within a certain temperature interval the drag current can be a descending function of the temperature $T$; 2) the experimentally observed temperature dependence $T^{-0.77}$ of the drag current can be interpreted within the framework of Fermi liquid theory; 3) at relatively high applied voltages the drag current as a function of the applied voltage saturates; 4) the screening of the electron potential by metallic gate electrodes can be of importance.

cond-mat.mes-hall↗

arXiv2008

Spin-magnetophonon level splitting in semimagnetic quantum wells

Spin-magnetophonon level splitting in a quantum well made of a semimagnetic wide gap semiconductor is considered. The semimagnetic semiconductors are characterized by a large effective $g$ factor. The resonance conditions $\hbarω_{\rm LO}=μ_BgB$ for the spin flip between two Zeeman levels due to interaction with longitudinal optical phonons can be achieved sweeping magnetic field $B$. This condition is studied in quantum wells. It is shown that it leads to a level splitting that is dependent on the electron-phonon coupling strength as well as on the spin-orbit interaction in this structure. We treat in detail the Rashba model for the spin-orbit interaction assuming that the quantum well lacks inversion symmetry and briefly discuss other models. The resonant transmission and reflection of light by the well is suggested as a suitable experimental probe of the level splitting.

cond-mat.other↗

arXiv2007

Vibrational instability, two-level systems and Boson peak in glasses

We show that the same physical mechanism is fundamental for two seemingly different phenomena such as the formation of two-level systems in glasses and the Boson peak in the reduced density of low-frequency vibrational states g(w)/w^2. This mechanism is the vibrational instability of weakly interacting harmonic modes. Below some frequency w_c << w_0 (where w_0 is of the order of Debye frequency) the instability, controlled by the anharmonicity, creates a new stable universal spectrum of harmonic vibrations with a Boson peak feature as well as double-well potentials with a wide distribution of barrier heights. Both are determined by the strength of the interaction I ~ w_c between the oscillators. Our theory predicts in a natural way a small value for the important dimensionless parameter C ~ 10^{-4} for two-level systems in glasses. We show that C ~ I^{-3} and decreases with increasing of the interaction strength I. We show that the number of active two-level systems is very small, less than one per ten million of oscillators, in a good agreement with experiment. Within the unified approach developed in the present paper the density of the tunneling states and the density of vibrational states at the Boson peak frequency are interrelated.

cond-mat.dis-nn↗

arXiv2007

A binuclear atom -- a special type of close bound state between proton and heavy atom

It is established within the Thomas -- Fermi model that a bound state of a proton with a heavy atom should exist. On the one hand, the electrons of the atom screen the proton's field. This decreases the repulsion force between the proton and the nucleus. On the other hand, the attraction force between the proton and the electrons is directed towards the gradient of the electron density, i. e. towards the nucleus. For instance, for Z=80 both forces become equal at approximately 0.6a where a is the Bohr radius. The corresponding minimum of the proton potential energy is in the region of negative energies (attraction) that can be of the order of several tens of eV. We propose to call such a system a binuclear atom. In contrast to the molecules where a coupling with a hydrogen atom is due to an essential modification of one or several states of the outer electrons the formation of a binuclear atom is a result of collective response of the whole system of inner electrons to the screened potential of a proton that is well inside the electron system of the heavy atom. The variation of the wave function of each electron can be considered as a small perturbation. The bound state is formed as a result of joint action of a large number of perturbed inner electrons. The important problem concerning the accuracy of our calculation within the Thomas -- Fermi model is discussed.

physics.atom-ph↗

arXiv2006

Spontaneous symmetry breaking in a system of strongly interacting multicomponent fermions (electrons with spin and conducting nanotubes)

We have calculated the ground state wave functions for a systems of multicomponent interacting fermions. We show that it describes the state with spontaneously broken chiral symmetry. In the limit of an infinitely strong interaction it turns into a phase with a finite density of chiral complexes. The number of particles constituting a complex depends on the number of fermion components. For example, in the case of two component electrons (spin) the condensate is built of four-particle complexes consisting of two "right" electrons and two "left" holes with the opposite spins.

cond-mat.str-el↗

arXiv2005

Thermoelectric effect in superconducting nanostructures

We study thermoelectric effects in superconducting nanobridges and demonstrate that the magnitude of these effects can be comparable or even larger than that for a macroscopic superconducting circuit. The reason is related to a possibility to have very large gradients of electron temperature within the nanobridge. The corresponding heat conductivity problems are considered. It is shown that the nanoscale devices allow one to get rid of masking effects related to spurious magnetic fields.

cond-mat.supr-con↗

arXiv2004

Pressure dependence of the Boson peak in glasses

The inelastic scattering intensities of glasses and amorphous materials has a maximum at a low frequency, the so called Boson peak. Under applied hydrostatic pressure, $P$, the Boson peak frequency, $ω_{\rm b}$, is shifted upwards. We have shown previously that the Boson peak is created as a result of a vibrational instability due to the interaction of harmonic quasi localized vibrations (QLV). Applying pressure one exerts forces on the QLV. These shift the low frequency part of the excess spectrum to higher frequencies. For low pressures we find a shift of the Boson peak linear in $P$, whereas for high pressures the shift is $\propto P^{1/3}$. Our analytics is supported by simulation. The results are in agreement with the existing experiments.

cond-mat.dis-nn↗

arXiv2004

Coulomb drag in longitudinal magnetic field in quantum wells

The influence of a longitudinal magnetic field on the Coulomb drag current created in the ballistic transport regime in a quantum well by a ballistic current in a nearby parallel quantum well is investigated. We consider the case where the magnetic field is so strong that the Larmour radius is smaller than the width of the well. Both in Ohmic and non-Ohmic case, sharp oscillations of the drag current as a function of the gate voltage or chemical potential are predicted. We also study dependence of the drag current on the voltage $V$ across the driving wire, as well as on the magnetic field $B$. Studying the Coulomb drag one can make conclusions about the electron spectrum and and electron-electron interaction in quantum wells.

cond-mat.mes-hall↗

arXiv2003

Anharmonicity, vibrational instability and Boson peak in glasses

We show that a {\em vibrational instability} of the spectrum of weakly interacting quasi-local harmonic modes creates the maximum in the inelastic scattering intensity in glasses, the Boson peak. The instability, limited by anharmonicity, causes a complete reconstruction of the vibrational density of states (DOS) below some frequency $ω_c$, proportional to the strength of interaction. The DOS of the new {\em harmonic modes} is independent of the actual value of the anharmonicity. It is a universal function of frequency depending on a single parameter -- the Boson peak frequency, $ω_b$ which is a function of interaction strength. The excess of the DOS over the Debye value is $\proptoω^4$ at low frequencies and linear in $ω$ in the interval $ω_b \ll ω\ll ω_c$. Our results are in an excellent agreement with recent experimental studies.

cond-mat.dis-nn↗

arXiv2002

Magnetophonon resonance in quantum wells in tilted field. What is concealed behind its angular dependence?

Magnetophonon resonance in quantum wells in a tilted magnetic field B is investigated. Measurements of the Hall coefficient and correspondingly of the carrier concentration as a functions of magnetic field and temperature are simultaneously performed. It is shown that the experimental data can be interpreted in terms of a great sensitivity of the effect to the variation of the two dimensional carrier concentration n in a certain concentration interval. In other words, the observed angular dependence of the MPR amplitudes is a manifestation of dependence of n on the magnitude of the magnetic field B.

cond-mat.str-el↗

arXiv2002

Is weak temperature dependence of electron dephasing possible?

The first-principle theory of electron dephasing by disorder-induced two state fluctuators is developed. There exist two mechanisms of dephasing. First, dephasing occurs due to direct transitions between the defect levels caused by inelastic electron-defect scattering. The second mechanism is due to violation of the time reversal symmetry caused by time-dependent fluctuations of the scattering potential. These fluctuations originate from an interaction between the dynamic defects and conduction electrons forming a thermal bath. The first contribution to the dephasing rate saturates as temperature decreases. The second contribution does not saturate, although its temperature dependence is rather weak, $\propto T^{1/3}$. The quantitative estimates based on the experimental data show that these mechanisms considered can explain the weak temperature dependence of the dephasing rate in some temperature interval. However, below some temperature dependent on the model of dynamic defects the dephasing rate tends rapidly to zero. The relation to earlier studies of the dephasing caused by the dynamical defects is discussed.

cond-mat.mes-hall↗

arXiv2002

Theory of magnetophonon resonance in 2D electron gas in tilted magnetic field

A theory of magnetophonon resonance in quantum wells in a magnetic field tilted to the perpendicular to 2DEG is developed. The resonance is due to the resonant interaction of 2D conduction electrons with the longitudinal optic phonons. The electrons are assumed to be nondegenerate. The angular dependence of the resonant maxima is investigated. The sharpness of the angular dependence, as well as the existence of double resonances, i.e. two resonant peaks for each resonance number is explained. A relation between the electron concentration dependence of the resonance amplitude in the perpendicular magnetic field and the angular dependence in the tilted field is analyzed. Investigation of the angular dependence can give information concerning the electron spectra, optic phonon and electron damping and the electron-phonon interaction in quantum wells.

cond-mat.mes-hall↗

arXiv2001

On the theory of thermoelectric phenomena in superconductors

The theory of thermoelectric effects in superconductors is discussed in connection to the recent publication by Marinescu and Overhauser, Phys. Rev. B 55, 11637 (1997). We argue that the charge on-conservation arguments by Marinescu and Overhauser do not require any revision of the Boltzmann transport equation in superconductors, and show that their ``electron-conserving transport theory'' contradicts thermodynamics. Possible mechanisms responsible for the discrepancy between some experimental data and the theory by Galperin, Gurevich, and Kozub, JETP Lett. 17, 476 (1973) are discussed.

cond-mat.supr-con↗

arXiv2001

Theory of shot noise in space-charge limited diffusive conduction regime

As is well known, the fluctuations from a stable stationary nonequilibrium state are described by a linearized nonhomogeneous Boltzmann-Langevin equation. The stationary state itself may be described by a nonlinear Boltzmann equation. The ways of its linearization sometimes seem to be not unique. We argue that there is actually a unique way to obtain a linear equation for the fluctuations. In the present paper we treat as an example an analytical theory of nonequilibrium shot noise in a diffusive conductor under the space charge limited regime. Our approach is compared with that of Schomerus, Mishchenko and Beenakker [Phys. Rev. B 60, 5839 (1999)]. We find some difference between the present theory and the approach of their paper and discuss a possible origin of the difference. We believe that it is related to the fundamentals of the theory of fluctuation phenomena in a nonequilibrium electron gas.

cond-mat.mes-hall↗

arXiv2000

Shot noise of Coulomb drag current

We work out a theory of shot noise in a special case. This is a noise of the Coulomb drag current excited under the ballistic transport regime in a one-dimensional nanowire by a ballistic non-Ohmic current in a nearby parallel nanowire. We predict sharp oscillation of the noise power as a function of gate voltage or the chemical potential of electrons. We also study dependence of the noise on the voltage V across the driving wire. For relatively large values of V the noise power is proportional to V^2.

cond-mat.mes-hall↗

arXiv2000

Non-Ohmic Coulomb drag in the ballistic electron transport regime

We work out a theory of the Coulomb drag current created under the ballistic transport regime in a one-dimensional nanowire by a ballistic non-Ohmic current in a nearby parallel nanowire. As in the Ohmic case, we predict sharp oscillation of the drag current as a function of gate voltage or the chemical potential of electrons. We study also dependence of the drag current on the voltage V across the driving wire. For relatively large values of V the drag current is proportional to V^2.

cond-mat.mes-hall↗