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SUMMARY:Magnetism of non-magnetic quantum magnets
DTSTART:20091207T161500
DTSTAMP:20260427T225210Z
UID:56b3e6c5c5ae951d36c28ab841fe9ff69ef108de2b20540647841a22
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Dr. Andrey Zheludev\nThe ground state of certain magneti
 c materials is totally disordered due to zero-point quantum spin fluctuati
 ons. Excitations in such "quantum spin liquids" are strongly interacting m
 agnons. Under appropriate conditions these quasiparticles demonstrate all 
 the fundamental properties of quantum Bose fluids. They are subject to the
  same type of interactions\, which may lead to peculiar instabilities\, si
 milar to the roton spectrum termination in superfluid 4He\, strong finite-
 T effects due to mutual scattering\, or even a total collapse of quasipart
 icle states. Obeying the same statistics\, quasiparticles in spin liquids 
 go through a sequence of quantum phase transitions between "Mott-insulator
 " and "superfluid" phases. These can be viewed in terms of Bose-Einstein c
 ondensation. However\, unlike the conventional BEC order parameter (wave f
 unction of the condensate)\, the magnetic analogue is an experimentally ob
 servable physical quantity. Like their counterparts in conventional quantu
 m fluids\, quasiparticles in spin liquids are subject to localization by a
 n external random potential. If the disorder is strong enough\, or the dim
 ensionality low enough\, BEC is preceded by a novel exotic state of bosoni
 c matter\, the so-called Bose glass. But spin liquids also demonstrate uni
 que phenomena\, such as chiral condensates and Luttinget liquid phases\, n
 ot realized in most conventional Bose fluids. \nExcellent realizations of 
 spin liquids are found in several prototypical magnetic materials\, with o
 ne- two or three-dimensional spin networks\, and with endless possibilitie
 s for interaction topologies. Chemical modifications provide opportunities
  to tweaking and fine-tuning the spin Hamiltionian and\, through it\, the 
 properties of quasiparticles. This opens a totally new experimental route 
 to understanding interacting Bosons.  Neutron diffraction and inelastic sc
 attering are especially useful\, as they provide direct access to the spin
  correlation functions. The latter are central to a qualitative interpreta
 tion of the underlying physics\, and are what the theorists typically like
  to calculate. \nIn this context\, in my talk I will review recent neutron
  scattering results for several quantum spin ladder and related materials.
LOCATION:Auditoire CE 4 - Centre Est
STATUS:CONFIRMED
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