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SUMMARY:Quantum Tricritical Points in NbFe2 - Dr. Sven Friedemann\, HH Wil
 ls Laboratory\, University of Bristol\, Bristol BS8 1TL\, UK
DTSTART:20170724T100000Z
DTEND:20170724T113000Z
UID:TALK74581@talks.cam.ac.uk
CONTACT:Alex Summerhill
DESCRIPTION:Quantum critical points (QCPs) emerge when a 2nd order phase t
 ransition is suppressed to zero temperature. In metals the quantum fluctua
 tions at such a QCP can give rise to new phases including unconventional s
 uperconductivity. Whereas antiferromagnetic QCPs have been studied in cons
 iderable detail\, ferromagnetic (FM) QCPs are much harder to access. In al
 most all metals FM QCPs are avoided through either a change to 1st order t
 ransitions or through an intervening spin-density-wave (SDW) phase. Here\,
  we study the prototype of the second case\, NbFe2. We demonstrate that th
 e phase diagram can be modeled using a two-order-parameter theory in which
  the putative FM QCP is buried within a SDW phase. We establish the presen
 ce of quantum tri-critical points (QTCPs) at which both the uniform and fi
 nite q susceptibility diverge. The universal nature of our model suggests 
 that such QTCPs arise naturally from the interplay between SDW and FM orde
 r and exist generally near a buried FM QCP of this type. Our results promo
 te NbFe2 as the first example of a QTCP\, which has been proposed as a key
  concept in a range of narrow-band metals\, including the prominent heavy-
 fermion compound YbRh2Si2.\n
LOCATION:Mott Seminar Room 531
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