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Université de Fribourg

Laser-pumped cesium magnetometers for the PSI-nEDM experiment

Gröger, Stephan ; Weis, Antoine (Dir.) ; Dousse, Jean-Claude (Codir.) ; Daum, Manfred (Codir.)

Thèse de doctorat : Université de Fribourg, 2005 ; Nr. 1487.

This thesis work describes the development of a high resolution magnetic field sensor for a fundamental research project of an international collaboration with participation of the Fribourg Atomic Physics Group. The goal of the collaboration is an experiment searching for an electric dipole moment of the neutron (nEDM), d, which will be performed at Paul Scherrer Institute (PSI). The possible...

Université de Fribourg

Electronic structure and optical properties of TaC from the first principles calculation

Sahnoun, Mohammed ; Daul, Claude A. ; Parlebas, J. C. ; Demangeat, C. ; Driz, M.

In: The European Physical Journal B, 2005, vol. 44, no. 3, p. 281-286

The electronic and optical properties of tantalum carbide TaC have been calculated using the full-potential linearized augmented-plane-wave method within the local density approximation scheme for the exchange-correlation potential. We find that the optical spectra can be extremely sensitive to the Brillouin zone sampling. The influence of relativistic effects on the dielectric function is...

Université de Fribourg

Modeling properties of molecules with open d-shells using density functional theory

Atanasov, Mihail ; Daul, Claude A.

In: Comptes Rendus Chimie, 2005, vol. 8(9-10), p. 1421-1433

An overview of the theory and applications of a recently proposed ligand-field density functional theory (LFDFT) is given. We describe a procedure based on DFT allowing to deduce the parameters of this non-empirical LF approach consisting of the following steps: (i) an average of configuration (AOC) DFT calculation, with equal occupancies of the d-orbitals is carried out (ii) with...

Université de Fribourg

Comparison of discharge lamp and laser pumped cesium magnetometers

Groeger, Stefan ; Pazgalev, Anatoly S. ; Weis, Antoine

In: Applied Physics B: Lasers and Optics, 2005, vol. 80(6), p. 645 - 654

We have performed a comparison of laser (LsOPM) and lamp (LpOPM) pumped cesium vapor magnetometers. Although the LsOPM operated 50% above its shot- noise limit we found an intrinsic sensitivity of 15 fT/√Hz and 25 fT/√Hz for the LsOPM and the LpOPM, respectively. Two modes of operation, viz. the phase-stabilized and the self-oscillating modes, were investigated and found to yield a similar...

Université de Fribourg

Large-scale gene discovery in the oomycete Phytophthora infestans reveals likely components of phytopathogenicity shared with true fungi

Dwyer, Rex A. ; Huitema, Edgar ; Beyer, Katinka ; Cvitanich, Cristina ; Kelkar, Hemant ; Ah Fong, Audrey M. V. ; Gates, Krista ; Roberts, Samuel ; Yatzkan, Einat ; Gaffney, Thomas ; Law, Marcus ; Testa, Antonino ; Torto-Alalibo, Trudy ; Zhang, Meng ; Zheng, Li ; Mueller, Elisabeth ; Windass, John ; Binder, Andres ; Birch, Paul R. J. ; Gisi, Ulrich ; Govers, Francine ; Gow, Neil A. ; Mauch, Felix ; West, Pieter van ; Waugh, Mark E. ; Yu, Jun ; Boller, Thomas ; Kamoun, Sophien ; Lam, Stephen T. ; Judelson, Howard S.

In: Molecular Plant-Microbe Interactions, 2005, vol. 18(3), p. 229

To overview the gene content of the important pathogen Phytophthora infestans, large-scale cDNA and genomic sequencing was performed. A set of 75,757 high-quality expressed sequence tags (ESTs) from P. infestans was obtained from 20 cDNA libraries representing a broad range of growth conditions, stress responses, and developmental stages. These included libraries from P....

Université de Fribourg

Laser-based precision magnetometry in fundamental and applied research

Weis, Antoine ; Wynands, Robert

In: Optics and Lasers in Engineering, 2005, vol. 43, p. 387-401

In this paper we review research done by the recently founded Fribourg group for Atomic Physics (FRAP) using laser-assisted spin coherence spectroscopy of atomic samples in applied and fundamental physics. Spin coherence in optically pumped ensembles of paramagnetic atoms may be extremely long-lived when the samples are well shielded from external perturbations, like static or oscillating...

Université de Fribourg

Circulating-current states and ring-exchange interactions in cuprates

Normand, Bruce ; Oleś, Andrzej M.

In: Physica C: Superconductivity, 2004, vol. 408-410, p. 252-253

We consider circulating charge- and spin-current states in a generalised Hubbard model for the CuO₂ planes in cuprates. We investigate the parameter regimes for these phases in microscopic calculations on small clusters. We demonstrate that a positive ring-exchange interaction enhances (suppresses) spin- (charge-)flux phases.

Université de Fribourg

Exchange constants and spin dynamics in Mn₁₂-acetate

Honecker, A. ; Fukushima, N. ; Normand, Bruce ; Chaboussant, G. ; Güdel, Hans-Ulrich

In: Journal of Magnetism and Magnetic Materials, 2005, vol. 290-291, p. 966-969

We have obtained new inelastic neutron scattering (INS) data for the molecular magnet Mn₁₂-acetate which exhibit at least six magnetic peaks in the energy range 5–35 meV. These are compared with a microscopic Heisenberg model for the 12 quantum spins localised on the Mn ions, coupled by four inequivalent magnetic exchange constants. A fit to the magnetic susceptibility under the constraint...

Université de Fribourg

Phase diagram of the Heisenberg spin ladder with ring exchange

Gritsev, Vladimir ; Normand, Bruce ; Baeriswyl, Dionys

In: Physical Review B, 2004, vol. 69, p. 094431-94446

We investigate the phase diagram of a generalized spin-1/2 quantum antiferromagnet on a ladder with rung, leg, diagonal, and ring-exchange interactions. We consider the exactly soluble models associated with the problem, obtain the exact ground states which exist for certain parameter regimes, and apply a variety of perturbative techniques in the regime of strong ring-exchange coupling. By...

Université de Fribourg

Exactly soluble isotropic spin-½ ladder models

Gritsev, Vladimir ; Baeriswyl, Dionys

In: Journal of Physics A: Mathematical and General, 2003, vol. 36, p. 12129-12142

The undeformed limit of the dilute two-colour braid–monoid algebra gives a natural basis for the description of spin-½ ladder models, and allows different Baxterization ansätze. Based on this observation we find the complete classification of exactly soluble generalized isotropic spin-½ ladder models.