Even after 25 years of intense research on the high temperature
superconducting cuprates it is still possible to either prove findings
which were not generally accepted, or even to find totally new results
which were not known before. In my talk, I will present new NMR
results on the prototypical HTSC compounds La2-xSrxCuO4 and YBa2Cu3Oy.
In the first compound, we could recently prove that the average low
temperature orthorhombic structure as determined by x-ray scattering
is fully compatible with its local structure determined by a local
probe as NMR [1]. In the second compound, we explored the highly
underdoped regime (y=6.35-6.6), and found a new NMR signal which
proves the emergence of a static order below a critical hole doping of
p_c ~ 0.095 [2].
Surprisingly, the pseudogap as determined by the NMR spin lattice
relaxation appears only above this critical doping level. Our data
suggests that a possibly stripe-like static order competes with the
spin-pseudogap phase, whereby both are separated by a critical hole
doping p_c.
[1] S.-H. Baek, A. Erb, B. Büchner, and H.-J. Grafe, Phys. Rev. B 85,
184508 (2012)
[2] S.-H. Baek, T. Loew, V. Hinkov, C. T. Lin, B. Keimer, B. Büchner,
and H.-J. Grafe, to be published
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