S. N. Klimin

Photoluminescence of spherical quantum dots

In order to interpret the phonon-assisted optical transitions in semiconductor quantum dots, a theory is developed comprising the exciton interaction with both adiabatic and Jahn-Teller phonons and also the external nonadiabaticity (pseudo-Jahn-Teller effect). The effects of nonadiabaticity of the exciton-phonon system are shown to lead to a significant enhancement of phonon-assisted transition probabilities and to multiphonon optical spectra that are considerably different from the Franck-Condon progression. The calculated relative intensity of the phonon satellites and its temperature dependence compare well with the experimental data on the photoluminescence of CdSe quantum dots, both colloidal and embedded in glass.

Theory of electron energy spectrum and Aharonov-Bohm effect in self-assembled Inx Ga1-x As quantum rings in GaAs

We analyze theoretically the electron energy spectrum and the magnetization of an electron in a strained

Multiphonon Raman scattering in semiconductor nanocrystals: importance of nonadiabatic transitions

{\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}∕\mathrm{Ga}\mathrm{As}

Bipolaron binding in quantum wires

self-assembled quantum ring (SAQR) with realistic parameters, determined from the cross-sectional scanning-tunneling microscopy characterization of that nanostructure. The SAQRs have an asymmetric indium-rich craterlike shape with a depression rather than an opening at the center. Although the real SAQR shape differs strongly from an idealized circular-symmetric open ring structure, the Aharonov-Bohm oscillations of the magnetization survive.

Polarons in an ellipsoidal potential well

Multi-phonon Raman scattering in semiconductor nanocrystals is treated taking into account both adiabatic and non-adiabatic phonon-assisted optical transitions. Because phonons of various symmetries are involved in scattering processes, there is a considerable enhancement of intensities of multi-phonon peaks in nanocrystal Raman spectra. Cases of strong and weak band mix- ing are considered in detail. In the first case, fundamental scattering takes place via internal electron-hole states and is participated by s- and d-phonons, while in the second case, when the intensity of the one-phonon Raman peak is strongly influenced by the interaction of an electron and of a hole with in- terface imperfections (e. g., with trapped charge), p-phonons are most active. Calculations of Raman scattering spectra for CdSe and PbS nanocrystals give a good quantitative agreement with recent experimental results.

Enhanced Probabilities of Phonon-Assisted Optical Transitions in Semiconductor Quantum Dots

A theory of bipolaron states in quantum wires with a parabolic potential well is developed applying the Feynman variational principle. The basic parameters of the bipolaron ground state (the binding energy, the no. of phonons in the bipolaron cloud, the effective mass, and the bipolaron radius) are studied as a function of sizes of the potential well. Two cases are considered in detail: a cylindrical quantum wire and a planar quantum wire. Anal. expressions for the bipolaron parameters are obtained at large and small sizes of the quantum well. It is shown that at R.mchgt.1 [where R means the radius (half width) of a cylindrical (planar) quantum wire, expressed in Feynman units], the influence of confinement on the bipolaron binding energy is described by the function .apprx.1/R2 for both cases, while at small sizes this influence is different in each case. In quantum wires, the bipolaron binding energy W(R) increases logarithmically with decreasing radius. The shapes and the sizes of a nanostructure, which are favorable for observation of stable bipolaron states, are detd. [on SciFinder (R)]

Effect of population imbalance on the Berezinskii-Kosterlitz-Thouless phase transition in a superfluid Fermi gas

Abstract Applying the Feynman variational principle, we analyze the basic polaron parameters – the ground-state energy, the polaron effective mass, the number of phonons in the polaron cloud, and the polaron radius – for a three-axis ellipsoidal potential well. Numerical calculations are performed for the specific cases when the potential well determines (i) a cylindrical quantum wire, (ii) a planar quantum wire, and (iii) a spherical quantum dot. The polaron parameters are derived analytically for the limiting cases of large and small cross-section sizes of a quantum wire, and of large and small radii of a quantum dot. A boundary between the weak and strong coupling regions is studied as a function of sizes of the structures under consideration. It is shown that with confinement strengthening, regions of the weak and intermediate coupling shorten, while the strong-coupling region widens. For a “squeezed” polaron state in a quantum dot, when the radius of confinement R is smaller than the polaron radius R p =(ℏ/ m ω 0 ) 1/2 (with the electron band mass m and the LO phonon frequency ω 0 ), the electron–phonon coupling constant α is scaled as αR p / R .

Interface superconductivity inLaAlO3−SrTiO3heterostructures

A theory of phonon-assisted optical transitions in semiconductor quantum dots is developed which takes into account the non-adiabaticity of the exciton-phonon system. The role of non-adiabaticity is shown to be of paramount importance in spherical quantum dots, where the lowest one-exciton state can be degenerate or quasi-degenerate. In quantum dots of lower symmetry, the effects of non-adiabaticity reveal themselves mainly due to the phonon-induced mixing of states which belong to different energy levels. Our approach is applied to explain the optical spectra of several quantum-dot structures: ensembles of spherical CdSe, CdSexS1-x and PbS quantum dots, self-assembled InAs/GaAs and CdSe/ZnSe quantum dots, brick-shaped InAs/GaAs quantum dots and CdS/HgS/CdS quantum dot heterostructures.

Wigner lattice of ripplopolarons in a multielectron bubble in helium

The Berezinskii-Kosterlitz-Thouless (BKT) mechanism describes the breakdown of superfluidity in a two-dimensional Bose gas or a two-dimensional gas of paired fermions. In the latter case, a population imbalance between the two pairing partners in the Fermi mixture is known to influence pairing characteristics. Here, we investigate the effects of imbalance on the two-dimensional BKT superfluid transition and show that superfluidity is even more sensitive to imbalance than for three-dimensional systems. Finite-temperature phase diagrams are derived using the functional integral formalism in combination with a hydrodynamic action functional for the phase fluctuations. This allows to identify a phase-separation region and tricritical points due to imbalance. In contrast to superfluidity in the three-dimensional case, the effect of imbalance is also pronounced in the strong-coupling regime.

Phase separation in imbalanced fermion superfluids beyond the mean-field approximation

The interface superconductivity in LaAlO3-SrTiO3 heterostructures reveals a nonmonotonic behavior of the critical temperature as a function of the two-dimensional density of charge carriers. We develop a theoretical description of interface superconductivity in strongly polar heterostructures, based on the dielectric function formalism. The density dependence of the critical temperature is calculated, accounting for all phonon branches including different types of optical (interface and half-space) and acoustic phonons. The longitudinal-optic- and acoustic-phonon mediated electron-electron interaction is shown to be the dominating mechanism governing the superconducting phase transition in the heterostructure.