Probing the Phase Diagram of Bi2Sr2CaCu2O8+d with Tunneling Spectroscopy

TL;DR

This study uses tunneling spectroscopy to explore how doping affects the electronic properties of Ca-rich Bi2Sr2CaCu2O8+d, revealing differences from stoichiometric samples and insights into the superconducting gap and disorder effects.

Contribution

It introduces a novel point contact tunneling method for Ca-rich Bi2212 and compares its doping-dependent spectral features to stoichiometric samples, highlighting disorder effects.

Findings

Ca-rich Bi2212 has a slightly smaller optimal Tc and gap.

Doping affects the tunneling conductance and spectral features.

Disorder from excess Ca broadens spectral features.

Abstract

Tunneling measurements are performed on Ca-rich single crystals of Bi2Sr2CaCu2O8+d (Bi2212), with various oxygen doping levels, using a novel point contact method. At 4.2 K, SIN and SIS tunnel junctions are obtained with well-defined quasiparticle peaks, robust dip and hump features and in some cases Josephson currents. The doping dependence of tunneling conductances of Ca-rich Bi2212 are analyzed and compared to stoichiometric Bi2212. A similar profile of energy gap vs. doping concentration is found although the Ca-rich samples have a slighly smaller optimum Tc and therefore smaller gap values for any doping level. The evolution of tunneling conductance peak height to background ratios with hole concentration are compared. For a given doping level, the Ca-rich spectra showed more broadened features compared to the stoichiometric counterparts, most likely due to increased disorder from the excess Ca. Comparison of the dip and hump features has provided some potential insights into their origins.