  Dynamical Dimension Reduction in Underdoped High Temperature Superconductors
G.G.Sergeeva (National Science Center "Kharkov Institute of Physics and
Technology",Ukraine),
  V.L.Vakula (B.Verkin Institute for Low Temperature Physics and Engineering of
the National Academy of Sciences of Ukraine)
  Abstract For underdoped cuprate HTSC we discuss the supposition that both the
pseudogap (PG) and supercoducting (SC) states result from dynamical dimension
reduction when HTSC behaves on cooling if its dimensionality is changed. It is
shown that the transition to the PG state occurs at the temperature T* as
dimensional crossover when charges motion changes from the three dimensional
(3D) to two-dimensional (2D). Namely two-dimensionality at T*>T is responsible
for the crucial role of Jahn-Teller (JT) distortions which bound up with holes
and form delocalized JT polarons and the localized three spin polarons in
copper-oxygen planes that removes the competition between pairing carriers and
their localization. At the cooling T*>T the SC transition occurs at Tc as a
sequence of the crossovers from zero-dimensional to 2D SC fluctuations, and
then to the 3D SC fluctuations. Some experimental evidence of the local hole-JT
polaron pairs and dynamical dimension reduction in the PG and SC states are
discussed.
