### Séminaire de groupe

UNIVERSAL FREE ENERGY DISTRIBUTION IN THE CRITICAL POINT OF A RANDOM ISING FERROMAGNET |

Yurij Holovatch |

ICMP, Lviv, Ukraine |

jeudi 20 novembre 2014 , 10h25 |

Salle de séminaire du groupe de Physique Statistique |

It is well known that the presence of weak quenched disorder in a ferromagnetic system can essentially modify its critical properties in the vicinity of the phase transition point such that new universal critical exponents may set in. On the other hand in recent years it is argued that due to the presence of disorder the statistical properties of some thermodynamical quantities at the critical point can become non-self-averaging. The aim of the present study is to demonstrate that due to the presence of weak disorder the statistics of the free energy fluctuations in the critical point of the Ising ferromagnet is described by a nontrivial universal distribution function. We discuss the non-self-averaging phenomena in the critical point of weakly disordered Ising ferromagnet. In terms of the renormalized replica Ginzburg-Landau Hamiltonian in dimensions D<4 we derive an explicit expression for the probability distribution function (PDF) of the critical free energy fluctuations. In particular, using known fixed-point values for the renormalized coupling parameters we obtain the universal curve for such PDF in the dimension D=3. It is demonstrated that this function is strongly asymmetric: its left tail is much more slow than the right one. <br> The work was done in collaboration with Victor Dotsenko. |