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SUMMARY:Hidden topological order in 1D Bose insulators - Ehud Altman (Weiz
 mann Institute)
DTSTART:20080428T143000Z
DTEND:20080428T153000Z
UID:TALK11102@talks.cam.ac.uk
CONTACT:6270
DESCRIPTION:Ground states of integer spin chains are known since the late 
 80's to sustain highly non local order described by infinite string operat
 ors of the spins. Such states defy the usual Landau theory description and
  can be considered simple prototypes of topological order. Recently we est
 ablished the existence of an analogous phase of spinless bosons\, which ex
 hibits similar string order in terms of the boson density. Moreover\, the 
 Bose system can be tuned across quantum phase transitions between the exot
 ic phase\, which we term Haldane insulator\, and the conventional Mott and
  density wave states. The response of the system to external perturbations
  near these phase transitions is revealing of the unusual character of the
  string order. In particular I will show how a perturbation\, seemingly un
 related by symmetry to either phase\, eliminates the critical point betwee
 n the Mott and Haldane phases and allows adiabatic connection between them
 . Finally I will establish the existence of a distinct collective mode tha
 t can serve to identify the new phase in Bragg spectroscopy experiments. \
 n
LOCATION:HEP Seminar Room (980) Rutherford Building\, Cavendish Laboratory
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