Evidence of two distinct charge carriers in underdoped high Tc cuprates

TL;DR

This study reveals that in underdoped high-Tc cuprates, different doping methods lead to distinct charge carriers, affecting superconductivity and normal metallic behavior, and challenges the conventional understanding of hole contribution.

Contribution

It demonstrates that doping mechanism influences whether holes contribute to superconductivity or only to metallic properties, suggesting a more nuanced view of correlated electronic bands.

Findings

Doping method determines the role of holes in superconductivity.

The number of mobile holes is not the sole factor for superconductivity.

Detailed phase diagram mapping shows complex doping effects.

Abstract

We present results on heavily underdoped Y_1-xCa_xBa_2Cu_3O_6+y which provide the evidence that the doping mechanism (cation substitution or oxygen loading) directly determines whether the corresponding injected mobile holes contribute to superconductivity or only to the normal metallic properties. We argue that this hole tagging calls for a subtler description of the correlated bands than the usual one. We also map in great detail the underdoped superconducting phase diagram T_c vs. hole doping which shows that the number of mobile holes is not the critical parameter for the superconductivity.