The energy-scale-dependent composite operator method for the single-impurity Anderson model

The recently developed energy-scale-dependent Composite Operator Method is applied to the single-impurity Anderson model. A fully self-consistent solution is given and analyzed. At very low temperatures, the density of states presents, on the top of the high-energy background, a Kondo-like peak whose parameter dependence is discussed in detail. The proposed method reproduces the exact results known in the literature with very low numerical effort and it is applicable for arbitrary values of the external parameters.Received: 24 September 2003, Published online: 9 April 2004PACS: 75.50.Ee Antiferromagnetics - 75.30.Et Exchange and superexchange interactions - 75.25. + z Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source X-ray scattering, etc.) - 75.50.-y Studies of specific magnetic materials     

Resonant States in High-Temperature Superconductors with Impurities

A microscopic theory of resonant states for the Zn-doped CuO₂ plane in the superconducting phase is formulated in the effective t–J model. In the model derived from the original p–d model, Zn impurities are considered as vacancies for the d states at Cu sites. In the superconducting phase, in addition to the local static perturbation induced by the vacancy, a dynamical perturbation appears that results in a frequency-dependent perturbation matrix. Using the T-matrix formalism for the Green's functions in terms of the Hubbard operators, we calculate the local density of electronic states with d, p, and s symmetries.     

Non-rigid hole band in the extended t-J model

Based on a simple matrix method, we investigate the effects of Fermi vector mismatch and elastic barrier on the dc Josephoson current through a ballistic, normal, one-dimensional quantum channel in contact with two superconducting electrodes. The coexistence of Andreev reflection and normal reflection forms quasibound states with open gaps in the normal conductor. The quantum transmission of individual electrons (or holes) gives new features to this mesoscopic system. The critical current character of a 2DEG coupled superconducting heterostructure with a length of sevral m0 is extensively studied. More importantly, our theoritical results are able to account for the recent anomalous experimental results.     

Phase resonances in one-dimensional disordered systems-analogy to classical mechanics

According to an analogy to classical mechanics phase resonances in disordered systems occur because of the sensitivity of closed orbits of an integrable system to an additional noise. This analogy permits a unified treatment of the phase resonances, which occur in disordered systems with a periodic background potential. Starting from a general model, we confirm exact results of Derrida and Gardner for the tight-binding model, discuss the influence of a finite correlation length in the nearly free electron case and generalize the work of Gorkov and Dorochov.     

Novel Carboxyl Esterase Preparations for the Resolution of Linalyl Acetate

 Biocatalytic resolution of the tertiary terpene alcohol (±)-linalool was accomplished via hydrolysis of its corresponding acetate ester using two highly enantiospecific enzymes (E > 100). The latter were identified in a crude cell-free extract of Rhodococcus ruber DSM 43338 and could be separated by (partial) protein purification. Since they showed opposite enantiopreference, they were termed (R)- and (S)-linalyl acetate hydrolase (LAH). The activity and selectivity of the enzyme preparations was markedly dependent on the fermentation conditions.     

The bandstructure of the copperoxide-plane including the singlet band

The effects of the Zhang-Rice singlet are included into the RPA-treatment of the Emery model by considering an additional singlet operator. The Fermi level of the doped, paramagnetic case is found within the singlet band. In agreement with the experiments, the dispersion of this band is similar to ordinary bandstructure calculations but it has a reduced bandwidth and is mainly of oxygen character.     

Evolution of the Fermi surface of cuprates on the basis of the spin-polaron approach

A classical field system is considered that consists of two interacting scalar fields, the Higgs real field and a complex scalar field. It is demonstrated that there exists a nontrivial topological solution in this system—a kink carrying a U(1) charge. Certain questions are discussed related to the stability of the solution obtained. An improved variational procedure is proposed for determining topological U(1)-charged configurations.     

Zn doping of YBa2Cu3O7 in melt textured materials: peak effect and high trapped fields

The previously introduced modified melt crystallization process (MMCP) has been applied to prepare single grain YBCO bulk material with Zn partially substituting for Cu. Hole doping was controlled by an appropriate oxidizing treatment of the as-grown bulk. A field induced pinning was indicated by a well pronounced peak of the critical current density j_c in the j_c vs. H relationship for the maximal oxidized (overdoped) material containing Zn, whereas pure overdoped YBCO shows no peak effect. The peak effect for Zn-doped YBCO appearing for T=77 K at a relatively high field of about 3 T can be attributed to pair breaking by locally induced magnetic moments due to in plane Zn for Cu substitution. Besides high quality of the bulk YBCO, the peak effect is the reason for the trapped field as large as 1.12 T at 77 K in the cylinder of only 25 mm in diameter.     

Electronic spectrum in a microscopical model for the Zn-doped CuO2 plane

We consider a microscopical model for the Zn-doped CuO₂ plane with Zn impurities being described as vacancies for the d-states on Cu sites. A reduction of the original p-d model to an effective one-band model results in the t-J model with vacancies for the spin 1/2 d-states at the Zn-sites. By employing the T-matrix formalism for the Green functions in terms of the Hubbard operators the density of electronic states (DOS) is calculated. Symmetry analysis of the perturbation matrix shows that in the system with d-type electronic wave functions additional DOS of d-, p- and s-types appear due to the perturbation of local energy levels and the interaction between nearest neighbors around the vacancy. The local and resonant state formation caused by Zn impurities is analyzed. Received 24 May 2000 and Received in final form 1 August 2000