Real space renormalization group with effective interactions: applications to 2-D spin lattices

The Blochs theory of effective Hamiltonians has been used to improve the Real Space Renormalization Group approach. The effective interactions between elementary blocks of a periodic lattice can be extracted from the knowledge of the spectrum of the dimers or trimers of blocks. The potentialities of the method are illustrated on a series of quasi 1-D and 2-D problems. The spin gap of two-leg ladders is calculated and an estimate of the impact of ferromagnetic couplings between two-leg ladders on the gap is presented. The method satisfactorily identifies the phase transitions in the 1/5-depleted square lattice as well as in the spin-frustrated Shastry-Sutherland lattice. The J ₂/J ₁ checkerboard lattice is studied and a location of the phase transition between the Néel phase and the dimer phase is proposed.Received: 11 June 2004, Published online: 30 September 2004PACS: 71.10.-W Theories and models of many-electron systems - 71.15.Nc Total energy and cohesive energy calculations - 75.10.-b General theory and models of magnetic ordering     

Ueber Untersuchung von Jodoform und Jod enthaltenden Verbandstoffen und Arzneimitteln

Ohne Zusammenfassung     

Electron quantum optics in ballistic chiral conductors

The edge channels of the quantum Hall effect provide one dimensional chiral and ballistic wires along which electrons can be guided in an optics‐like setup. Electronic propagation can then be analyzed using concepts and tools derived from optics. After a brief review of electron optics experiments performed using stationary current sources which continuously emit electrons in the conductor, this paper focuses on triggered sources, which can generate on‐demand a single particle state. It first outlines the electron optics formalism and its analogies and differences with photon optics and then turns to the presentation of single electron emitters and their characterization through the measurements of the average electrical current and its correlations. This is followed by a discussion of electron quantum optics experiments in the Hanbury‐Brown and Twiss geometry where two‐particle interferences occur. Finally, Coulomb interactions effects and their influence on single electron states are considered.     

Melting curve of NaCl0.5Br0.5 up to 4.5 GPa

Abstract

The melting curve of NaCl_0.5Br_0.5 has been measured under pressure up to 4.5 GPa. The melting temperatures of Ag and NaCl have been used to determine the pressure in the sample at its melting temperature.     

Etude de grenats ferrimagnetiques d'yttrium substitues au scandium: Influence de la pression sur leur stabilite et leur temperature de curie

The garnets Y₃Fe₅O₁₂ and Y₃Fe_4.1Sc_0.9O₁₂ are unstable under high temperature and high pressure. They decompose into YFeO₃ and an iron oxide, usually Fe₃O₄. The high temperature decomposition is favoured by pressure and it spreads over a range of temperature which is larger for the substituted garnet than for the pure garnet. The experiments carried out on Y₃Fe₅O₁₂ corroborate the results of Marezio and Geller but do not show the existence of a dense form of this compound, in opposition to the conclusions presented by Shimada.The Curie temperature θ of the garnets Y₃Fe_5?xSc_x O₁₂ (x = 0,35, 0,70 and 0,90) has been measured under pressure up to 60 kbar. The Curie temperature increases under pressure according to the law θ_x (P) = θ_x (0)[ 1 + fP + hp²]. Thef and h coefficients are almost the same for the studied garnets and their average values are f = 2,07 · 10^?3kbar^?1andh = minus;8,37 · 10^?6kbar^?2. Our results are in agreement with what can be inferred from the theories of Geller and Rosencwaig. In addition, the law suggested by Bloch for the Néel ferrimagnetic compounds d Log θ/d Log $\text{V ? ?}\text{10}\text{3}$ can be also applied to these compounds.