QFS2016 Book of Abstracts

Abstracts

O1.8 Condensation of helium in a silica aerogel: a realization of the athermal Random Field Ising Model Geoffroy Jacques Aubry(1), Victor Doebele(1), Edouard Kierlik(2), Panayotis Spathis(1), Pierre-Etienne Wolf(1)

1) Institut Neel, Universitee Grenoble Alpes/CNRS 2) LPTMC, Universite Pierre et Marie Curie/CNRS

We experimentally study the condensation of 4 He in light silica aerogels to probe the effect of dilute disorder on a first order phase transition. Using light scattering to measure the fluid state on a local scale, we show that our system is well described by the, out-of-equilibrium, athermal, Random Field Ising Model (RFIM) introduced by Sethna et al (PRL 70, 3347, 1993). Specifically, we evidence the two phenomena predicted by this model. i) A disorder driven critical point (Aubry et al, PRL 113, 085301, 2014) ii) A microscopic Return Point Memory along minor hysteresis loops. Our measurements are the first to demonstrate these two effects in a single physical system. O1.9 Quantum degradation of the second order phase transition S.M. Stishov, A.E. Petrova Institute for High Pressure Physics of RAS, Troitsk, Russia The specific heat, magnetization and thermal expansion of single crystals of antiferromagnetic insulator EuTe, were measured at temperatures down to 2 K and in magnetic fields up to 90 kOe. The heat capacity and thermal expansion coefficient reveal λ -type anomalies at the second order magnetic phase transition at low magnetic fields, evolving to simple jumps at high magnetic fields and low temperatures, well described in a fluctuation free mean-field theory. The experimental data and the corresponding analysis favor the quantum concept of effective increasing space dimensionality at low temperatures that suppresses a fluctuation divergence at a second order phase transition

20