Scaling behavior of the normal-state properties of the underdoped high-T c cuprates

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The scaling behavior of the normal state transport and magnetic properties of the underdoped cuprates as a function of T/T<SUB>0</SUB> is now interpreted as an evidence for the opening of a pseudogap at T* approximately T<SUB>0</SUB>. To investigate the origin of the pseudogap, we have analyzed first the temperature dependence of the resistivity (rho) (T) of the novel Sr<SUB>2.5</SUB>Ca<SUB>11.5</SUB>Cu<SUB>24</SUB>O<SUB>41</SUB> spin-ladder compound under hydrostatic pressure of up to 8 GPa. This (rho) (T) dependence has been successfully explained by assuming that the relevant length scale for electrical transport -- the inelastic length -- is given by the magnetic correlation length related to the opening of a spin-gap in a one- dimensional (1D) even-chain spin-ladder (1D-SL). As a next step, we compared the (rho) (T) curves of the SL compounds and underdoped cuprates. We have found that the (rho) (T) dependences of YBa<SUB>2</SUB>Cu<SUB>4</SUB>O<SUB>8</SUB> and underdoped YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>x</SUB> demonstrate a remarkable scaling with the (rho) (T) of the 1D-SL compound Sr<SUB>2.5</SUB>Ca<SUB>11.5</SUB>Cu<SUB>24</SUB>O<SUB>41</SUB>. This scaling implies that the pseudo-gap below T* in underdoped YBa<SUB>2</SUB>Cu<SUB>4</SUB>O<SUB>8</SUB> and YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>x</SUB> is the spin-gap in the even-chain 1D-SL formed at T less than T* in these materials. Therefore, at temperatures T<SUB>c</SUB>(x) less than T less than T*(x), underdoped cuprates are effectively in a 1D ('stripe') regime. A Josephson-like coupling of these stripes leads to a recovery of a 2D regime at low temperatures T approximately T<SUB>c</SUB>(x).