Abstract

The low-temperature normal-state resistivities of underdoped ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}$ crystals with ${T}_{c}$ of 20 and 35 K were studied by suppressing the superconductivity with pulsed magnetic fields of 61 T. Both in-plane resistivity ${\ensuremath{\rho}}_{\mathrm{ab}}$ and out-of-plane resistivity ${\ensuremath{\rho}}_{c}$ are found to diverge logarithmically as $\frac{T}{{T}_{c}}\ensuremath{\rightarrow}0$. Logarithmic divergence is accompanied by a nearly constant anisotropy ratio, $\frac{{\ensuremath{\rho}}_{c}}{{\ensuremath{\rho}}_{\mathrm{ab}}}$, suggesting an unusual three-dimensional insulator.