Two-Dimensional Localization and Superconductor-Insulator Transition in Strongly Underdoped Single Crystals ofY1−xPrxBa2Cu3O7−δ

Abstract

In-plane $({\ensuremath{\rho}}_{\mathrm{ab}})$ and out-of-plane $({\ensuremath{\rho}}_{c})$ normal state resistivities of insulating ${\mathrm{PrBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ and superconducting ${\mathrm{Y}}_{0.47}{\mathrm{Pr}}_{0.53}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ $({T}_{c}\ensuremath{\approx}18\mathrm{K})$ crystals have been measured using a ``flux transformer'' method. In the insulating sample we have found that ${\ensuremath{\rho}}_{c}/{\ensuremath{\rho}}_{\mathrm{ab}}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}a+bT}^{\ensuremath{-}2/3}$ over two decades of temperature, which indicates two-dimensional localization. By suppressing the onset of superconductivity with a magnetic field, we have observed that low ${T}_{c}$ ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ is transformed into a 2D insulator with transport properties similar to those of ${\mathrm{PrBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$.