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SUMMARY:Quantum criticality in iron-based superconductors - Antony Carring
 ton\, HH Wills Physics Laboratory\, University of Bristol
DTSTART:20141211T111500Z
DTEND:20141211T121500Z
UID:TALK56106@talks.cam.ac.uk
CONTACT:Helen Verrechia
DESCRIPTION:Iron pnictide/chalcogenide superconductors present a so-far un
 ique new perspective on the field of unconventional superconductivity. The
  materials have a relatively high superconducting transition temperature a
 nd in contrast to the cuprates\, multi-band\, mult-orbital physics plays a
  key role but Mott physics less so. One unique property is that the struct
 ure of the superconducting gap function has an unprecedented variation bet
 ween the different compounds. In some cases\, there is a clearly identifia
 ble quantum critical point in the temperature – doping phase diagram and
  this presents an excellent opportunity to study how quantum critical fluc
 tuations affect (or perhaps cause) the superconducting state.\nIn this tal
 k I will review experiments identifying the quantum critical point (QCP) i
 n the iron-pnictide superconductor series BaFe2(As1-xPx)2.  de Haas-van Al
 phen\, magnetic penetration depth and heat capacity results all show clear
  signatures of a diverging mass at its QCP.  The proximity of the QCP yiel
 ds unexpected anomalies in the superconducting critical fields. We find th
 at both the lower and upper critical fields strongly violate the expectati
 ons from conventional theory taking into account the observed mass enhance
 ment near the QCP. This implies that the energy of superconducting vortice
 s is enhanced\, possibly due to a microscopic mixing of antiferromagnetism
  and superconductivity\, suggesting that a highly unusual vortex state is 
 realised in quantum critical superconductors.\n
LOCATION:Mott Seminar Room (531)\, Cavendish Laboratory\, Department of Ph
 ysics
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