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M. Yu. Kuchiev

Publications and source records attributed to M. Yu. Kuchiev.

50 records · Page 3Linked to original sources
arXiv1997

The bulk Josephson responce of the d-g-wave cuprate superconductor

We consider the implications of the small Fermi surface for the ab-plane microwave absorption. The small Fermi surface results in two superconducting condensates. Linear combinations of these condensates correspond to the d- and g-wave pairings. Microwave electric field applied in the ab-plane induces Josephson transitions between the condensates. Dependence of the absorption upon direction, amplitude and frequency of the external microwave field is calculated. Results of the calculation are compared with the observed recently novel non-linear phenomena in microwave absorption of $YBaCu_2O_{7-δ}$ single crystals.

cond-mat.supr-con↗
arXiv1997

Post-Collision Interaction with Wannier electrons

A theory of the Post-Collision Interaction (PCI) is developed for the case when an electron atom impact results in creation of two low-energy Wannier electrons and an ion excited into an autoionizing state. The following autoionization decay exposes the Wannier pair to the influence of PCI resulting in variation of the shape of the line in the autoionization spectrum. An explicit dependence of the autoionization profile on the wave function of the Wannier pair is found. PCI provides an opportunity to study this wave function for a wide area of distances

physics.atom-ph↗
arXiv1997

Multiphoton detachment from negative ions: new theory vs experiment

In this paper we compare the results of our adiabatic theory (Gribakin and Kuchiev, Phys. Rev. A, accepted for publication) with other theoretical and experimental results, mostly for halogen negative ions. The theory is based on the Keldysh approach. It shows that the multiphoton detachment rates and the corresponding n-photon detachment cross sections depend only on the asymptotic behaviour of the bound state radial wave function. The dependence on the exponent is very strong. This is the main reason for the disagreement with some previous calculations, which employed bound state wave functions with incorrect asymptotic forms. In a number of cases our theoretical results produces best agreement with absolute and relative experimental data.

physics.atom-ph↗
arXiv1997

Multiphoton detachment of electrons from negative ions

A simple analytical solution for the problem of multiphoton detachment from negative ions by a linearly polarized laser field is found. It is valid in the wide range of intensities and frequencies of the field, from the perturbation theory to the tunneling regime, and is applicable to the excess-photon as well as near-threshold detachment. Practically, the formulae are valid when the number of photons is greater than two. They produce the total detachment rates, relative intensities of the excess-photon peaks, and photoelectron angular distributions for the hydrogen and halogen negative ions, in agreement with those obtained in other, more numerically involved calculations in both perturbative and non-perturbative regimes. Our approach explains the extreme sensitivity of the multiphoton detachment probability to the asymptotic behaviour of the bound-state wave function. Rapid oscillations in the angular dependence of the $n$-photon detachment probability are shown to arise due to interference of the two classical trajectories which lead to the same final state after the electron emerges at the opposite sides of the atom when the field is close to maximal.

physics.atom-ph↗
arXiv1996

The search for ``polarized'' instantons in the vacuum

The new phase of a gauge theory in which the instantons are ``polarized'', i.e. have the preferred orientation is discussed. A class of gauge theories with the specific condensates of the scalar fields is considered. In these models there exists an interaction between instantons resulting from one-fermion loop correction. The interaction makes the identical orientation of instantons to be the most probable, permitting one to expect the system to undergo the phase transition into the state with polarized instantons. The existence of this phase is confirmed in the mean-field approximation in which there is the first order phase transition separating the ``polarized phase'' from the usual non-polarized one. The considered phase can be important for the description of gravity in the framework of the gauge field theory.

hep-th↗
arXiv1996

Adiabatic mechanism of the multiply charged ion production by a laser field through ATI states of an atom

ATI can be followed by an inelastic collision of the ionized electron with the parent atomic particle resulting in an excitation of the ion. It may be a continuum state excitation producing the doubly charged ion or a discrete state which also enhances the doubly charged ion production. Absorption of a few quanta above the atomic threshold is sufficient to make this mechanism work. As a result the two-electron processes can take place even in moderate fields. The example of two-electron excitations of He atoms in a 780 nm laser field with intensity above $ 10^{14}$W/cm$^2$ is discussed

atom-ph↗
arXiv1996

ATI as a source for multiply charged ion production in a laser field

A theory for the many-electron multi-photon process is presented. It is shown that after single-electron excitation into some level in the continuum (ATI) an inelastic collision of the excited electron with the parent atomic particle can result in an excitation of the ion. It may be the continuum state excitation giving the doubly charged ion or the discrete state which also greatly enhances the doubly charged ion production. The probability of these phenomena greatly exceeds that of the direct ionization of a single-charged ion. The single-electron ATI makes possible the two-electron process even in the moderate field. The example of two-electron excitations of He atom in a 780 nm laser field with intensity above $\approx 10^{14}$W/cm$^2$ is discussed.

atom-ph↗
arXiv1995

Interaction of instantons in a gauge theory forcing their identical orientation

A gauge theory model in which there exists a specific interaction between instantons is considered. An effective action describing this interaction possesses a minimum when the instantons have identical orientation. The considered interaction might provide a phase transition into the state where instantons have a preferred orientation. This phase of the gauge-field theory is important because it can give the description of gravity in the framework of the gauge theory.

hep-th↗
arXiv1995

Many Body Correlation Corrections to Superconducting Pairing in Two Dimensions.

We demonstrate that in the strong coupling limit (the superconducting gap $Δ$ is as large as the chemical potential $μ$), which is relevant to the high-$T_c$ superconductivity, the correlation corrections to the gap and critical temperature are about 10\% of the corresponding mean field approximation values. For the weak coupling ($Δ\ll μ$) the correlation corrections are very large: of the order of 100\% of the corresponding mean field values.

cond-mat↗
arXiv1995

Two-hole bound states in modified t-J model

We consider modified $t-J$ model with minimum of single-hole dispersion at the points $(0,\pm π)$, $(\pm π,0)$. It is shown that two holes on antiferromagnetic background produce a bound state which properties strongly differs from the states known in the unmodified $t-J$ model. The bound state is d-wave, it has four nodes on the face of the magnetic Brillouin zone. However, in the coordinate representation it looks like as usual s-wave.

supr-con↗
arXiv1994

Polarization of Instantons and Gravity

Gravity can arise in a conventional non-Abelian gauge theory in which a specific phenomenon takes place. Suppose there is a condensation of polarized instantons and antiinstantons in the vacuum state. Then the excitations of the gauge field in the classical approximation are described through the variables of Riemann geometry satisfying the Einstein equations of general relativity. There are no dimensional coupling constants in the theory.

hep-th↗
arXiv1994

Large size two-hole bound states in t-J model

Several series of shallow large-size ($l \gg lattice~ spacing$) two-hole bound states are found in the two-dimensional t-J model. Their binding energies depend exponentially on the inverse value of the hole-spin-wave coupling constant. Their parity is connected with the angular wave function in a nonstandard way. The possible role of these states in the formation of superconducting pairing is considered.

cond-mat↗
arXiv1994

The hole-hole superconducting pairing in t-J model induced by the long-range spin-wave exchange

Long-range $(r \sim p_F^{-1} \gg lattice \ spacing)$ spin-wave exchange produces a very strong pairing of the holes. The different symmetry solutions of BCS-type equation for the superconducting gap $Δ$ are found. The most strong pairing corresponds to $d$-wave symmetry. The physical reasons for the strong pairing are: 1)large velocity of the spin-wave, 2) a ``collapse'' effect in the attractive potential (-1/r^2) describing the interaction between two holes induced by spin-wave exchange. 3)strongly asymmetric hole dispersion. At concentration of the holes $δ\sim 0.01-0.3$ we get $Δ\sim T_c \sim ε_F$. At very low concentration of the holes the many-body wave function of the ground state decays into the product of two-hole bound states.

cond-mat↗