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DTSTAMP:20260414T164201
DTSTART:20150522T133000
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DTEND:20150522T133000
URL:https://murmitoyen.com/events/vanille/udem/detail/611142
LOCATION:Université de Montréal - Pavillon Roger-Gaudry\, 2900\, chemin d
 e la Tour\, Montréal\, QC\, Canada\, H3T 1J6
SUMMARY:Soutenance de doctorat de Roger Muller
DESCRIPTION:Topological order in a broken symmetry stateIn contrast to an o
 rdinary topological insulator\, in an antiferromagnetic topological insula
 tor (AFTI) the presence  of magnetic order breaks time reversal symmetry
  as well as primitive-lattice translational symmetry\,  yet the product 
 of both symmetry operations is preserved. This allows the definition of a 
 new topological invariant that characterizes  a topological state with a
 ntiferromagnetic order. Depending on hether the surface breaks  this com
 bined symmetry or not\, metallic surface states may arise within the band 
 gap and a half-integer  quantum Hall effect is expected. Moreover\, the 
 presence of the topological phase is bound to the antiferromagnetic  pha
 se and so vanishes above the Néel temperature. This makes the AFTI articu
 larly interesting\, as the topological state  appears only after the sys
 tem undergoes a  lassical phase transition. Therefore\, changing the temp
 erature allows one to  turn the topological phase on or off\, resulting 
 in a quantum phase transition at the Néel temperature.  Within this fra
 mework we have investigated two possible candidate materials of the half-H
 eusler\, REBiPt family\,  for this new ground state of matter. The REBi
 Pt family shows many interesting properties such as superconductivity\, an
 tiferromagnetic order\,  and super-heavy-fermion behaviour. Band structu
 re calculations and ARPES experiments  on Lu\, Nd\, and GdBiPt indicate 
 the presence of metallic surface states that differ  strongly from the b
 and structure in the bulk.  On this background we have carried out singl
 e crystal and powder neutron and X-ray diffraction experiments\,  to det
 ermine the magnetic structure of GdBiPt and NdBiPt\, as their crystalline 
 structure have the necessary symmetries for being AFTI.
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