Transport Properties of Bi$_2$Sr$_{2-x}$La$_x$CaCu$_2$O$_{8+\delta}$ Single Crystals Grown by a Floating-Zone Method

TL;DR

This study reports the successful growth of Bi-based high-$T_c$ superconductor single crystals using a floating zone method, revealing metallic-like resistivity and itinerant holes in the parent insulator.

Contribution

It demonstrates a new crystal growth technique for Bi-based superconductors and provides insights into the electronic properties of the parent insulator.

Findings

In-plane resistivity shows metallic behavior near room temperature.

Hall mobility in the parent insulator is similar to that of doped samples.

The system is not a simple insulator; holes are itinerant upon doping.

Abstract

A parent insulator of the Bi-based high-$T_c$ superconductor Bi$_2$Sr$_{2-x}$La$_x$CaCu$_2$O$_{8+\delta}$ was successfully grown by a traveling solvent floating zone method. The in-plane resistivity $\rho_{ab}$ shows metallic behavior ($d\rho_{ab}/dT >$ 0) near room temperature, although the magnitude of the resistivity is far above the Mott limit for metallic conduction. The Hall mobility of the parent insulator does not so much differ from that of an optimally doped sample. These results suggest that the system is not a simple insulator with a well-defined gap, and the hole in the parent insulator is essentially itinerant, as soon as it is doped.