Pseudogap formation and superconductivity of Bi$_{1.74}$Pb$_{0.38}$Sr$_{1.88}$CuO$_{6+\delta}$ by studies of out-of-plane resistivity in magnetic fields

TL;DR

This study investigates the out-of-plane resistivity of Bi-based cuprate superconductors under magnetic fields, identifying two characteristic temperatures and clarifying the relationship between pseudogap and superconducting gap.

Contribution

It provides new insights into the pseudogap formation and its relation to superconductivity by analyzing resistivity and magnetoresistance in magnetic fields.

Findings

Identification of two characteristic temperatures $T^*$ and $T^{**}$.

Correlation of $T^{**}$ with the pseudogap temperature.

Distinct phenomena associated with $T^*$ and $T^{**}$.

Abstract

We report the out-of-plane resistivity in the systematically oxygen-controlled single crystals Bi$_{1.74}$Pb$_{0.38}$Sr$_{1.88}$CuO$_{6+\delta}$ in magnetic fields parallel to the c-axis. Two characteristic temperatures $T^*$ and $T^{**}$ are found at which a semiconductor-like upturn starts to develop and the magnetoresistance changes its sign from positive to negative at lower temperature, respectively. The obtained phase diagram strongly suggests that the pseudogap temperature correlating to the superconducting gap is not $T^{*}$ but $T^{**}$. The gap opened at $T^*$ may relate to another phenomenon with the different energy scale such as the antiferromagnetic excitation due to the exchange interaction between Cu$^{2+}$ spins.