The renormalization group for disordered systems

• Main Author: Castellana, Michele
• Language: ENG
• Published: Université Paris Sud - Paris XI 2012
• Subjects: [PHYS:COND:CM_GEN] Physics/Condensed Matter/Other; Spin glasses; Structural glasses; Renormalization group
• Online Access: http://tel.archives-ouvertes.fr/tel-00694469; http://tel.archives-ouvertes.fr/docs/00/69/44/69/PDF/VD2_CASTELLANA_MICHELE_31012012.pdf; http://tel.archives-ouvertes.fr/docs/00/69/44/69/ANNEX/VD2_CASTELLANA_MICHELE_31012012_synthI_se.pdf

In this thesis we investigate the employ of the renormalization group for glassy systems. More precisely, we focus on models of spin glasses and structural glasses. Spin-glass models represent disordered uniaxial magnetic materials, such as a dilute solution of Mn in Cu, modeled by an array of spins on the Mn arranged at random in the matrix of Cu, and interacting with a potential which oscillates as a function of the separation of the spins. Structural glasses are liquids that have been cooled fast enough to avoid crystallization, like o-Terphenyl or Glycerol. Spin and structural glasses are physically interesting because their critical properties are known only in the limit where the space dimensionality tends to infinity, i. e. in the mean-field approximation. A fundamental question is whether the physical properties characterizing these systems in the mean-field case still hold for real spin or structural glasses, which live in a space with a finite number of dimensions. The spin and structural glasses that we study in this thesis are models built up on hierarchical lattices, which are the simplest non-mean field systems where the renormalisation group approach can be implemented in a natural way. The features emerging from this implementation clarify the critical behavior of these systems. As far as the finite-dimensional spin glass studied in this thesis is concerned, we developed a new technique to implement the renormalization group transformation for finite-dimensional spin glasses. This technique shows that the system has a finite-temperature phase transition characterized by a critical point where the system's correlation length is infinite. As far as the structural glass studied in this thesis is concerned, this is the first structural glass model where we showed the existence of a phase transition beyond mean field. The ideas introduced in this work can be further developed in order to understand the structure of the low-temperature phase of these systems, and in order to establish whether the properties of the low-temperature phase holding in the mean-field case still hold for finite-dimensional glassy systems.