We present fully self-consistent calculations in the fluctuation exchange approximation for the half-filled Hubbard model in 2D. A non-fermi liquid state evolves with decreasing temperature in this self-consistent model of coupled spin fluctuations and quasiparticles. The mean field phase transition to long-range antiferromagnetic order is suppressed and we find no evidence of a phase transitio...

Various types ordering processes in systems with large fluctuation are overviewed. Generally, the so-called order-disorder phase transition takes place in competition between the interaction causing the system be ordered and the entropy causing a random disturbance. Nature of the phase transition strongly depends on the type of fluctuation which is determined by the structure of the order param...

We study the four dimensional Gaussian spin glass in presence of a magnetic field. Using off-equilibrium numerical simulations we have found that the probability distribution of the overlaps is built in the same way as that of the Mean Field approximation with replica symmetry breaking. Finally we have studied the violation of the fluctuation-dissipation theorem in presence of magnetic field.

2014 The charge density oscillations in Al 3d alloys are discussed and the observed values, which are strongly reduced with respect to the values predicted by Friedel’s expression, are explained using the localised spin fluctuation approximation of the Anderson model. Temperature dependence of 039403C1 is discussed as well. LE JOURNAL DE PHYSIQUE LETTRES ~ TOME 38, ler FÉVRIER 1977,

Fluctuation effects in nematic-type phases in quantum systems of spin 1 and 9 are examined. The analogue of the Mermin-Wagnertheoremis formulated and the perturbation theory is shown to be logarithmically divergent under certain conditions. The low-energy excitations depend on the parity of 2s.

In this note, we show how to generalize the stochastic calculus method introduced by Comets and Neveu [3] for two models of spin glasses, namely the SK model with external field and the perceptron model. This method allows to derive quite easily some fluctuation results for the free energy in those two cases.

A theoretical description is presented for low-temperature magnetic-field induced threedimensional (3D) ordering transitions in strongly anisotropic quantum antiferromagnets, consisting of weakly coupled antiferromagnetic spin-1/2 chains and ladders. First, effective continuum field theories are derived for the one-dimensional subsystems. Then the Luttinger parameters, which determine the low-t...

The interplay of disorder and spin-fluctuation effects in a disordered antiferromagnet is studied. In the weak-disorder regime (W<U), while the energy gap decreases rapidly with disorder, the sublattice magnetization, including quantum corrections, is found to remain essentially unchanged in the strong correlation limit. Magnon energies and Néel temperature are enhanced by disorder in this limi...

We study the out-of-equilibrium dynamics of the fully-frustrated XY model. At equilibrium, this model undergoes two phase transitions at two very close temperatures: a Kosterlitz-Thouless topological transition and a secondorder phase transition between a paramagnetic phase and a low-temperature phase where the chiralities of the lattice plaquettes are anti-ferromagnetically ordered. We compute...

The Schwinger boson mean field theory is applied to the quantum ferrimagnetic Heisenberg chain. There is a ferrimagnetic long range order in the ground state. We observe two branches of the low lying excitation and calculate the spin reduction, the gap of the antiferromagnetic branch, and the spin fluctuation at T = 0K. These results agree with the established numerical results quite well. At f...