Note: in brackets [ ] an important result from a given subfield and the reference which I co-authored are indicated.
My lifelong research interest has been condensed matter physics, concentrating mostly on quantum theory of electronic structure and properties of condensed matter systems. Outside of this microscopic approach I contributed to three topics, Dispersion relations [ Kramers-Kronig relations in determining optical constants, Czech. J. Phys. 11, 787 (1961)], Zone melting [ultimate distribution of impurity, Phys. Stat. Sol. (b) 5, 207 (1964)], and, notably, Granular systems [ultrasound propagation in externally stressed granular media, Phys. Rev. Lett. 82, 1863 (1999)]. From the field of Optical properties of crystalline semiconductors I select one result, [modeling hyperbolic excitons, Phys. Stat. Sol. (b) 16, 147 (1966)]. Concerning disordered systems, I worked in two areas. In the field of Substitutional Alloys I was involved in development of modern Green function tools, in particular of the Coherent potential approximation (CPA) [Phys. Rev. 175, 747 (1968)] and its applications [paramagnetic alloys: electronic density of states, Phys. Rev. B 1, 3250 (1970), electronic structure of (Cd,Hg)Te, Phys. Rev. B 27, 1088 (1983), electronic states in mixed Cd1−xPbxF2 crystals, Sol. State Comm. 58, 663 (1986)]. A popular technical detail was given in three variants [simplification of Green's-function calculations through analytic continuation, Phys. Rev. B 29, 3697 (1984); Phys. Stat. Sol. (b) 134, 659 (1986); J. Phys. C: Solid State Phys. 19, 7173 (1986)]. Of the work on Amorphous semiconductors, I may refer to my early justification of the Tauc edge reproduced in the Appendix of [Tauc, J.; Grigorovici, R.; Vancu, A. (1966). "Optical Properties and Electronic Structure of Amorphous Germanium". Physica Status Solidi B 15 , 627], and, of the material oriented papers, to [Refractive Index of Crystalline and Amorphous GeS, Phys. Stat. Sol. (b) 104, K95 (1981)]. In Surface physics I single out the derivation of [surface Green function by matching, J. Phys. C: Solid State Phys. 4, L104 (1971)]. In Quantum transport, two papers were important, [electronic transport in disordered binary alloys: coherent-potential approximation, Phys. Rev. 184, 614 (1969)] and [Generalized Kadanoff-Baym Ansatz (GKBA) for deriving quantum transport equations, Phys. Rev. B 34, 6933 (1986)]. Since the latter paper, I worked on a systematic theory of far non-equilibrium non-stationary electronic processes using Non-equilibrium Green’s functions combined with GKBA. This has led to the concept of non-equilibrium quasiparticles, to a non-equilibrium Ward identity, and to the so-called Reconstruction theorem, as summarized in [Fortschr. Phys. 65, No. 6–8, 1700032 (2017)]. Recently, I participate in the study of transient currents through nanoscopic molecular bridges linking bulk metal electrodes. The path to the quantum transport equations based on GKBA works well for normal metal electrodes, but fails for magnetic tunneling between the ferromagnetic ones. A first breakthrough was achieved by supplementing the Ansatz by asymptotic vertex corrections [EPL, 121 (2018) 67002], [ Phys. Status Solidi B 2019, 256 1800594]