Chemical potential jump between hole- and electron-doped sides of ambipolar high-Tc cuprate

TL;DR

This study measures the intrinsic chemical potential difference between hole- and electron-doped high-Tc cuprates using core-level XPS, revealing a smaller jump than optical gaps due to charge excitation and polaronic effects.

Contribution

First direct estimation of the true chemical potential jump in a single high-Tc cuprate system doped with both holes and electrons.

Findings

Chemical potential jump is approximately 0.8 eV.

The jump is smaller than the optical gap of 1.4-1.7 eV.

Charge-excitation gap and polaronic effects influence the jump.

Abstract

In order to study an intrinsic chemical potential jump between the hole- and electron-doped high-Tc superconductors, we have performed core-level X-ray photoemission spectroscopy (XPS) measurements of Y0.38La0.62Ba1.74La0.26Cu3Oy (YLBLCO), into which one can dope both holes and electrons with maintaining the same crystal structure. Unlike the case between the hole-doped system La_2-xSrxCuO4 and the electron-doped system Nd_2-xCexCuO4, we have estimated the true chemical potential jump between the hole- and electron-doped YLBLCO to be ~0.8 eV, which is much smaller than the optical gaps of 1.4-1.7 eV reported for the parent insulating compounds. We attribute the reduced jump to the indirect nature of the charge-excitation gap as well as to the polaronic nature of the doped carriers.