BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Memento EPFL//
BEGIN:VEVENT
SUMMARY:Fermi arc evolution and doping mechanism in high-temperature super
 conductors
DTSTART:20141212T141500
DTSTAMP:20260609T072228Z
UID:6c707bb6e2be4768e3c5d0b5e3d3ff670c9bfd21d7f43e61f9867c98
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Denis K. Sunko\, Department of Physics\, Faculty of Scie
 nce\, University of Zagreb\, Croatia\nWe calculate realistic Fermi surface
  (FS) evolution of La2-x Srx CuO4  (LSCO) with Sr doping within an extens
 ive ab-initio framework including advanced band-unfolding techniques. We s
 how that ordinary  Kohn-Sham DFT+U can reproduce the observed metal-insul
 ator transition and arc growth\, when not restricted to the paramagnetic s
 olution space. We elucidate both arc protection and the inadequacy of ther
 igid-band picture as consequences of a rapid change in orbital symmetry at
  the Fermi energy: the material undergoes a dimensional crossover along th
 e Fermi surface\, between the nodal (2D) and antinodal (3D) regions. In LS
 CO\, this crossover accounts for FS arcs\, the antinodal pseudogap\, and i
 nsulating behavior in c-axis conductivity\, all ubiquitous phenomena in hi
 gh-Tc  cuprates. The same calculation shows that the Sr hole stays locali
 zed in the vicinity of the dopand atom\, indicating that metallization of 
 the Cu-O plane is due to an orbital transition between Cu and O planar sit
 es\, originally proposed by Mazumdar in 1989. We can directly observe effe
 cts of the transition in charge transfers among in-plane atoms\, which are
  different than predicted by non-interacting coherent models. This “ioni
 c doping” mechanism has close parallels to modern views on the metalliza
 tion of interfaces.\nThe orbital transition is experimentally confirmed by
  replacing 4% of planar Cu in nearly optimally doped YBa2Cu3O6.92  powder
  with isotopically pure 67 Zn\, lowering Tc  to 57 K. The pure nuclear qu
 adrupole resonance (NQR) spectrum of 67 Zn\, measured for the first time\,
  shows that each Zn dopand surrounds itself with an AF insulating cluster.
  We conclude that Zn destroys the SC metal by a Coulombic “domino effect
 ” which reverts the orbital transition locally and pushes a significant 
 number of surrounding sites back towards the parent-compound configuration
 \, as suggested by Mazumdar in 1990. An unexpected asymmetry of the NQR si
 gnal is traced to the same splitting of the planar oxygens as the LTT tilt
  in LSCO\, also well known to lower Tc  strongly. This elevates the intra
 -unit-cell oxygen splitting to a universal microscopic antagonist of SC in
  the cuprates\, shedding an interesting light on the SC mechanism.
LOCATION:PH L1 503 (Aquarium) http://plan.epfl.ch/?room=PHL1503
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR