BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//wp-events-plugin.com//6.4.7.2//EN
TZID:Europe/Paris
X-WR-TIMEZONE:Europe/Paris
BEGIN:VEVENT
UID:1-158@lptms.universite-paris-saclay.fr
DTSTART:20130719T100000Z
DTEND:20130719T130000Z
DTSTAMP:20130712T050700Z
URL:https://www.lptms.universite-paris-saclay.fr/seminars/soutenance-de-th
 ese-arthur-lavarelo/
SUMMARY:Soutenance de thèse : Arthur Lavarélo - LPTMS-batiment 100\, sall
 e des conseils - 19 Juil 13 10:00
DESCRIPTION:Frustration and disorder in quantum spin chains and ladders\nAr
 thur Lavarélo\nIn quantum spins systems\, frustration and low-dimensional
 ity generate quantum fluctuations and give rise to exotic quantum phases. 
 This thesis studies a spin ladder model with frustrating couplings along t
 he legs\, motivated by experiments on cuprate BiCu2PO6.\nFirst\, we presen
 t an original variational method to describe the low-energy excitations of
  a single frustrated chain. Then\, the phase diagram of two coupled chains
  is computed with numerical methods. The model exhibits a quantum phase tr
 ansition between a dimerized phase and resonating valence bound (RVB) phas
 e. The physics of the RVB phase is studied numerically and by a mean-field
  treatment. In particular\, the onset of incommensurability in the dispers
 ion relation\, structure factor and correlation functions is discussed in 
 details.  Then\, we study the effects of non-magnetic impurities on the ma
 gnetization curve and the Curie law at low temperature. A low-energy effec
 tive model is derived within the linear response theory and is used to exp
 lain the behaviors of the magnetization and Curie constant.  Eventually\, 
 we study the effect of bonds disorder\, on a single frustrated chain. The 
 variational method\, introduced in the non-disordered case\, gives a low d
 isorder picture of the dimerized phase instability\, which consists in the
  formation of Imry-Ma domains delimited by localized spinons.
LOCATION:LPTMS-batiment 100\, salle des conseils\, 15 Rue Georges Clemencea
 u\, Orsay\, France
GEO:48.698200;2.181770
X-APPLE-STRUCTURED-LOCATION;VALUE=URI;X-ADDRESS=15 Rue Georges Clemenceau\,
  Orsay\, France;X-APPLE-RADIUS=100;X-TITLE=LPTMS-batiment 100\, salle des 
 conseils:geo:48.698200,2.181770
END:VEVENT
END:VCALENDAR