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URL:https://murmitoyen.com/events/vanille/udem/detail/559997
LOCATION:Université de Montréal - Pavillon J.-Armand-Bombardier\, 5155\, 
 chemin de la rampe \, Montréal\, QC\, Canada\, H3T 2B2
SUMMARY:Complex electronic order in pnictide superconductors studied by nuc
 lear probe spectroscopy – Hans-Henning Klauss\, TU Dresden\, Germany
DESCRIPTION:Hans-Henning Klauss\, TU Dresden\, Institut für Festkörperph
 ysik\, Helmholtzstraße 1001069 Dresden\, Deutschland.The interplay of it
 inerant magnetism and unconventional superconductivity in Fe based superco
 nductors and other intermetallic systems with complex Fermi surfaces is a 
 fascinating topic in contemporary correlated electron physics.In my talk I
  will discuss Mössbauer spectroscopy and muon spin relaxation experiments
  on several series of hole doped 122 pnictides like Ba1−xKxFe2As2 [1]. I
  will present new data on Ca1−xNaxFe2As2 (x = 0.35\, 0.50 and 0.67). The
  parent compound CaFe2As2 shows a spin density wave order below TN = 165 K
  [2\,3]. Our microscopic study proves that with increasing Na-substitution
  level\, the magnetic order parameter as well as the magneto-structural ph
 ase transition is suppressed. For x = 0.50 we find a microscopic coexisten
 ce of magnetic and superconducting phases accompanied by a reduction of th
 e magnetic order parameter below the superconducting transition temperatur
 e Tc. A systematic comparison with other 122 pnictides reveals a linear co
 rrelation between the magnetic order parameter reduction and the ratio of 
 the transition temperatures\, Tc/TN\, which can be understood in the frame
 work of a Landau-theory.  In the optimally doped specimen with Tc ≈ 34 
 K\, the temperature dependence of the penetration depth and superfluid den
 sity were obtained\, which proves the presence of two superconducting s-wa
 ve gaps.I will also discuss multigap superconductivity with broken time re
 versal symmetry in locally non-centrosymmetric SrPtAs.  µSR experiments 
 prove the development of a small static spontaneous internal field just be
 low Tc\, evidencing the time reversal symmetry (TRS) breaking SrPtAs [4].
   75As-NMR\, and NQR-nvestigations clearly reveal a two step behaviour in
  the spin-lattice relaxation rate evidencing multigap superconductivity wi
 th very weak inter-band coupling and constraints for the possible pairing 
 symmetries. Unconventional chiral d-wave or f-wave order parameters are co
 nsistent with our data [5]. E. Wiesenmayer et al.\, Phys. Rev. Lett. 107\
 , 237001 (2011). K. Zhao et al.\, Phys. Rev. B 84\, 184534 (2011)G. Wu et
  al.\, Journal of Physics: Condensed Matter 20\, 422201 (2008).F. Brückne
 r et al.\, Phys. Rev. B 90\, 220503 (2014).Voici le lien vers la page web 
 du groupe de recherche du Pr KlaussCette conférence est présentée par 
 le RQMP Versant Nord du Département de physique de l'Université de Mont
 réal et le Département de génie physique de Polytechnique Montréal.
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