M. Ya. Amusia

Scaling behavior of heavy fermion metals

Strongly correlated Fermi systems are fundamental systems in physics that are best studied experimentally, which until very recently have lacked theoretical explanations. This review discusses the construction of a theory and the analysis of phenomena occurring in strongly correlated Fermi systems such as heavy-fermion (HF) metals and two-dimensional (2D) Fermi systems. It is shown that the basic properties and the scaling behavior of HF metals can be described within the framework of a fermion condensation quantum phase transition (FCQPT) and an extended quasiparticle paradigm that allow us to explain the non-Fermi liquid behavior observed in strongly correlated Fermi systems. In contrast to the Landau paradigm stating that the quasiparticle effective mass is a constant, the effective mass of new quasiparticles strongly depends on temperature, magnetic field, pressure, and other parameters. Having analyzed the collected facts on strongly correlated Fermi systems with quite a different microscopic nature, we find these to exhibit the same non-Fermi liquid behavior at FCQPT. We show both analytically and using arguments based entirely on the experimental grounds that the data collected on very different strongly correlated Fermi systems have a universal scaling behavior, and materials with strongly correlated fermions can unexpectedly be uniform in their diversity. Our analysis of strongly correlated systems such as HF metals and 2D Fermi systems is in the context of salient experimental results. Our calculations of the non-Fermi liquid behavior, the scales and thermodynamic, relaxation and transport properties are in good agreement with experimental facts.

Two-electron photoionization of helium

Cross sections of such processes as double photoionization and photoionization accompanied by excitation of He-like atomic systems are investigated in the limit of high, but still not relativistic, photon energies. In addition to total cross sections electron energy and angular distributions are also obtained. Coulomb wave and Green functions were employed in the momentum representation. Results for the total double ionization cross section as a function of photon energy are close to those obtained by predecessors with much more complicated ground state wavefunctions. The cross section of ionization with simultaneous excitation differs considerably from those obtained before. Angular and energy distributions of ionized electrons, are, to this extent, investigated for the first time.

Interference effects in photoionization of noble gas atoms outer s-subshells

A strong influence of ns2np6 → ns2np5 ϵd transition on the outer ns subshell photoionization cross section of noble gas atomsis demonstrated.

Angular distribution of photoelectrons with many-electron correlations

Abstract The angular distribution of electrons in the noble gas photoionization is calculated with many-electron correlations taken into account in the random phase approximation with exchange.

Photodetachment of negative C60− ions

Abstract A model that describes the electron structure of negative fullerene C60− ions is proposed. The model contains only two experimentally observed parameters, namely the fullerene radius and the affinity energy of the electron to neutral C60. In the frame of this model, cross sections are calculated of elastic scattering of slow electrons on neutral fullerene, of C60− photodetachment near the threshold of this process and of radiative recombination of slow electrons with neutral fullerenes.

On the possibility of considering the fullerene shell C60 as a conducting sphere

Abstract The dynamical and static dipole polarizabilities of the C 60 molecule have been calculated on the basis of the experimental data on the cross section of the fullerene photoabsorption. It has been shown that the fullerene shell in the static electric field behaves most likely as a set of separate carbon atoms rather than as a conducting sphere.

The theory of collective motion probed by light

A review of collective phenomena in atomic and quasi-atomic systems is presented. The fundamental unity of the subject is stressed by appealing to a simple conceptual scheme, namely the Landau theory of wave propagation applied to a Fermi fluid. Collective giant resonances in nuclei, atoms, metallic clusters and fullerenes are all discussed and related to each other. Single-photon dipole, two-photon and quadrupole excitation are considered, as well as the observation of harmonics, and the enhancement of double excitations by a giant resonance. Other near-threshold phenomena are discussed, and experiments involving strong-field lasers are also considered in this context.

Relative intensities in x-ray photoelectron spectra. Part VI. The spectra of He(I), He(II), Y Mζ and Zr Mζ☆

The 2s- and 2p-electron photoionization cross-sections at photon energies up to 190 eV have been calculated, using the RPAE method for averaged configurations of the C, N, O and Ne atoms. The RPAE method ensures a more accurate relation between the cross-sections, 2s/2p, than that obtained using the Hartree—Fock method. Within the framework of the Gelius—Siegbahn model, but with the use of theoretical atomic cross-sections, we have calculated the photoionization cross-sections for He(I), He(II), Y Mζ, Zr Mζ for CH4, C2H6, C3H8, C2H4, C2H2, NH3, H2O, CN−, N2, CO, CO2, N2O and NO2− molecules. For CO, N2, CO2, N2O and H2O molecules, a comparison is made between the theoretical and experimental cross-sections for hν < 60 eV. The calculated absolute and relative values of the molecular-orbital cross-sections are in reasonable agreement with experiment, especially at hν ⩾ 40 eV. The calculations correctly reproduce the change in intensities under the transition He(I) → He(II). We have shown that our calculations have a significant advantage over those performed using the PW and OPW approximations. It is shown for NO, N2, CO, H2O, CH4, NH3 and N2O molecules that the total photoionization cross-section calculated taking into account the real structure of the molecular orbitals is in better agreement with the experimental photoabsorption cross-section than is the sum of the cross-sections for the atoms in a molecule.

Quasiparticle picture of high-temperature superconductors in the frame of a Fermi liquid with the fermion condensate

A model of a Fermi liquid with the fermion condensate (FC) is applied to the consideration of quasiparticle excitations in high-temperature superconductors, in their superconducting and normal states. Within our model the appearance of the fermion condensate presents a quantum phase transition that separates the regions of normal and strongly correlated electron liquids. Beyond the phase transition point the quasiparticle system is divided into two subsystems, one containing normal quasiparticles and the other{emdash}fermion condensate localized at the Fermi surface and characterized by almost dispersionless single-particle excitations. In the superconducting state the quasiparticle dispersion in systems with FC can be presented by two straight lines, characterized by effective masses M{sub FC}{sup *} and M{sub L}{sup *}, respectively, and intersecting near the binding energy, which is of the order of the superconducting gap. This same quasiparticle picture persists in the normal state, thus manifesting itself over a wide range of temperatures as new energy scales. Arguments are presented that fermion systems with FC have features of a {open_quotes}quantum protectorate{close_quotes} [R. B. Laughlin and D. Pines, Proc. Natl. Acad. Sci. U.S.A. >97, 28 (2000); P. W. Anderson, cond-mat/0007185 (unpublished); cond-mat/0007287 (unpublished)].

Dramatic distortion of the 4d giant resonance by the C60 fullerene shell

The photoionization cross section for the endohedral Xe@C60 atom is investigated within the framework of representing the C60 by a delta-type potential. Results demonstrate that in Xe@C60, the 4d giant resonance is distorted significantly when compared with that of the isolated Xe atom. The reflection of the photoelectron waves by the C60 causes strong oscillations in the photoionization cross section resulting in the replacement of the Xe 4d giant resonance by four prominent peaks. The approximation of C60 by an infinitely thin real potential preserves reasonably well the sum rule for the 4d electrons but modifies the dipole polarizability of the 4d shell.