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SUMMARY:Non-Fermi-liquid scattering rates and anomalous band dispersions i
 n ironpnictides and ironchalcogenides - an ARPES study
DTSTART:20151127T141500
DTSTAMP:20260528T235408Z
UID:81bb40b2fef309c227b4ddb98f2763fa0df41c3a200275328571019e
CATEGORIES:Conferences - Seminars
DESCRIPTION:Jörg H. Fink\nHost: Davor Pavuna\nLeibniz Institute for Solid
  State and Materials Research Dresden\,\nUnconventional/high temperature s
 uperconductivity (SC) is observed in heavy fermion systems\, cuprates\, mo
 lecular crystals\, and ferropnictides close to a point in the phase diagra
 m where\, as a function of a control parameter such as pressure\, chemical
  pressure\, or doping\, the antiferromagnetic order is suppressed. A wides
 pread view is that at this point\, which is called a quantum critical poin
 t\, strong antiferromagnetic fluctuations are a candidate for the glue med
 iating superconductivity and that these fluctuations would also account fo
 r the strange normal state non-Fermi-liquid behavior as is visible in tran
 sport and thermal properties. Using angle-resolved photoemission spectrosc
 opy (ARPES) we have studied the scattering rates and band dispersion of va
 rious iron pnictides and iron chalcogenides as a function of the control p
 arameter. The detected scattering rates of all electron and hole pockets d
 o not diverge at optimal doping\, i.e.\, at the expected quantum critical 
 point. This result is at variance with the above described scenario for qu
 antum critical behavior. The scattering rates strongly differ for pockets 
 having different orbital character\, and are linear in energy\, indicating
  marginal Fermi liquid behavior. The scattering rates for hole doped compo
 unds are considerably larger than those of the electron doped systems\, in
 dicating a dependence on the Fe 3d count leading for a 3d5 configuration t
 o a strongly correlated Hund’s metal. Near optimal doping the measuremen
 ts also indicate a crossing of the top of hole or electron pockets\, throu
 gh the Fermi level which is related to Lifshitz transitions. Based on thes
 e experimental results together with calculations\, we establish the follo
 wing scenario which is different from the traditional view related to stro
 ng fluctuations at the quantum critical point: a co-action between a highl
 y correlated electron liquid and a Lifshitz transition causes an anomalous
  band dispersion at the Fermi level which leads to a strong mass enhanceme
 nt in the normal state\, detected in the transport and thermal properties
   and to a small effective Fermi energy favoring a Bardeen-Cooper-Schrief
 fer - Bose-Einstein crossover state in the superconducting phase. The resu
 lts can be generalized to other unconventional superconductors.
LOCATION:CE 1 5 https://plan.epfl.ch/?room==CE%201%205
STATUS:CONFIRMED
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