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SUMMARY:Search for Stripes in Lightly Hole Doped YBa2Cu3O6 by ESR and IR T
 ransmission - András Jánossy (Budapest University of Technology and Econ
 omics)
DTSTART:20061108T111500Z
DTEND:20061108T121500Z
UID:TALK5565@talks.cam.ac.uk
CONTACT:Michael Sutherland
DESCRIPTION:We present a series of electron spin resonance (ESR) and infra
 red (IR) transmission experiments in antiferromagnetic lightly hole doped 
 YBa2Cu3O6 in search for the effect of a spatially inhomogeneous ground sta
 te on the magnetic and electric properties. Crystal compositions were Ca_x
 Gd_yY_(1-x-y)Ba_2Cu_3O_6 with x=0\, 0.008\, 0.02 and 0.03\; Gd is an ESR p
 robe that does not effect the electronic structure. We show that holes are
  not preferentially localized at low temperatures in the vicinity of Ca do
 pants. We mapped the antiferromagnetic domain structure as a function of h
 ole concentration\, temperature and magnetic fields up to 8 T. We find a h
 ole doping induced rotation of the magnetic easy axis from collateral to d
 iagonal with respect to the tetragonal CuO2 lattice. We argue that at low 
 temperatures the AF magnetization is pinned to a static modulation or a ph
 ase separated network of the hole density. The dominantly fourfold symmetr
 y of pinning suggests that the hole density network has fourfold symmetry 
 and is not an array of stripes. We discuss the possibility of AF domain wa
 ll fluctuations at higher temperatures. We measured IR transmission under 
 magnetic field in search of an anisotropy of the conductivity at finite fr
 equencies. A small zero frequency anisotropy has been interpreted by Ando 
 et al. as arising from the rotation of stripes in a magnetic field. We fin
 d no anisotropy and conclude that while the antiferromagnetic domain struc
 ture is weakly pinned\, the network of holes is rigid and is not affected 
 by magnetic fields.
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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