Valery I. Rupasov

Bethe Ansatz Approach to the Thermodynamics of Superconducting Magnetic Alloys

We derive thermodynamic Bethe ansatz equations for a model describing an

EXACTLY SOLVABLE MODEL OF SUPERCONDUCTING MAGNETIC ALLOYS

U\to\infty

Temperature and size-dependent suppression of Auger recombination in quantum-confined lead-salt nanowires

Anderson impurity embedded in a BCS superconductor. The equations are solved analytically in the zero-temperature limit, T=0. It is shown that the impurities depress superconductivity in the Kondo limit, however at T=0 the system remains in the superconducting state for any impurity concentration. In the mixed-valence regime, an impurity contribution to the density of states of the system near the Fermi level overcompensates a Cooper pairs weakening, and superconductivity is enhanced.

Electronic structure and optical properties of quantum-confined lead salt nanowires

Abstract A model describing the Anderson impurity embedded in a BCS superconductor is proven to exhibit hidden integrability and is diagonalized exactly by the Bethe ansatz.

HIDDEN INTEGRABILITY OF A KONDO IMPURITY IN AN UNCONVENTIONAL HOST

Auger recombination (AR) of the ground biexciton state in quantum-confined lead-salt nanowires (NWs) with a strong coupling between the conduction and the valence bands is shown to be strongly suppressed, and only excited biexciton states contribute to Auger decay. The AR rate is predicted to be greatly reduced when temperature or the NW radius are decreased, and the effect is explained by decrease in both the population of excited biexciton states and overlap of phonon-broadened single-exciton and biexciton states. Suppression of AR of multiexciton states exhibiting strong radiative decay makes obviously lead-salt NWs a subject of special interest for numerous lasing applications.

Kondo screening in gapless magnetic alloys

In the framework of four-band envelope-function formalism, developed earlier for spherical semiconductor nanocrystals, we study the electronic structure and optical properties of quantum-confined lead salt (PbSe and PbS) nanowires (NWs) with a strong coupling between the conduction and the valence bands. We derive spatial quantization equations, and calculate numerically energy levels of spatially quantized states of a transverse electron motion in the plane perpendicular to the NW axis, and electronic subbands developed due to a free longitudinal motion along the NW axis. Using explicit expressions for eigenfunctions of the electronic states, we also derive analytical expressions for matrix elements of optical transitions and study selection rules for interband absorption. Next we study a two-particle problem with a conventional long-range Coulomb interaction and an interparticle coupling via medium polarization. We derive analytical expressions for an effective direct Coulomb coupling and an effective coupling via medium polarization averaging corresponding coupling energies over the fast transverse motion of charge carriers and then compute numerically the effective couplings for the lowest-energy electron-hole pair in a PbSe NW of the radius

EXACTLY SOLVABLE MODELS OF UNCONVENTIONAL MAGNETIC ALLOYS : BETHE ANSATZ VERSUS RENORMALIZATION-GROUP METHOD

R=5\text{ }\text{nm}

Quantum Gap Solitons and Many-Polariton-Atom Bound States in Dispersive Medium and Photonic Band Gap.

in vacuum. The obtained results show that due to a large magnitude of the high-frequency dielectric permittivity of PbSe material, and hence, a high dielectric NW/vacuum contrast, the effective coupling via medium polarization significantly exceeds the effective direct Coulomb coupling at all interparticle separations along the NW axis. Furthermore, the strong coupling via medium polarization results in a bound state of the longitudinal motion of the lowest-energy electron-hole pair (a longitudinal exciton) while fast transverse motions of charge carriers remain independent of each other. For a PbSe NW of the radius

MULTIPHOTON LOCALIZATION AND PROPAGATING QUANTUM GAP SOLITONS IN A FREQUENCY GAP MEDIUM

R=5\text{ }\text{nm}

Resonance Raman scattering in photonic band-gap materials

, the binding energy of the longitudinal exciton is found to be about 77.9 meV that is approximately two times smaller than the energy of spatial quantization of the lowest-energy electronic states. Thus, the strong interparticle coupling via medium polarization in quantum-confined lead salt NWs significantly modifies the single-particle electronic spectrum and could result in essential modifications such Coulomb phenomena as impact ionization, Auger recombination, and carrier multiplication.