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We report and analyze in-plane penetration depth measurements in YBa2Cu3O7-x taken close to the critical temperature Tc. In underdoped YBa2Cu3O6:59 we find consistent evidence for charged critical behavior. Noting that the effective dimensionless charge scales as 1/sqrt(Tc), this new critical behavior should be generically observable in suitably underdoped cuprates.
The preformed-pairs theory of pseudogap physics in high-$T_C$ superconductors predicts a nonanalytic $T$-dependence for the $ab$-plane superfluid fraction, $rho_S$, at low temperatures in underdoped cuprates. We report high-precision measurements of
By comparison of recent direct measurements of the temperature dependence of the upper critical field $H_{c2}$ in an Y-123 high temperature superconductor with the scaling analysis of magnetization data, collected in fields H << H_c2, we demonstrate
Evidence of two-dimensional (2D) quantum critical fluctuations is observed in the superfluid density ns(T) propto $lambda$ -2(T) of deeply underdoped Bi2Sr2CaCu2O8+x (Bi-2212) films, indicating that quantum fluctuations play a dominant role in underd
We report a polarized neutron scattering study of the orbital-like magnetic order in strongly underdoped ${rm YBa_2Cu_3O_{6.45}}$ and ${rm YBa_2(Cu_{0.98}Zn_{0.02})_3O_{6.6}}$. Their hole doping levels are located on both sides of the critical doping
The magnetic spectrum at high-energies in heavily underdoped YBa$_{2}$Cu$_{3}$O$_{6.35}$ (T$_{c}$=18 K) has been determined throughout the Brillouin zone. At low-energy the scattering forms a cone of spin excitations emanating from the antiferromagne