Abstract

A 61-T pulsed magnetic field suppresses superconductivity in ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ single crystals and reveals an insulator-to-metal (IM) crossover for both in-plane resistivity ${\ensuremath{\rho}}_{\mathrm{ab}}$ and $c$-axis resistivity ${\ensuremath{\rho}}_{c}$ at a Sr concentration near optimum doping ( $x\ensuremath{\simeq}0.16$). The IM transition is unusual in that all underdoped samples ( $x<0.16$) show low-temperature insulating behavior, even in samples with linear- $T$ ${\ensuremath{\rho}}_{\mathrm{ab}}$ above ${T}_{c}$ and apparently large ${k}_{F}l$.