Direct visualization of ambipolar Mott transition in cuprate CuO2 planes

TL;DR

This study visualizes the Mott transition in cuprate CuO2 planes across doping regimes, revealing a Fermi level shift with unchanged Mott-Hubbard bands, providing insights into high-temperature superconductivity.

Contribution

It presents the first real-space visualization of the ambipolar Mott transition in cuprates, showing systematic Fermi level shifts while maintaining the Mott-Hubbard structure.

Findings

Fermi level shifts systematically with doping

Mott-Hubbard band structure remains unchanged

Supports self-modulation doping framework

Abstract

Identifying the essence of doped Mott insulators is one of the major outstanding problems in condensed matter physics and the key to understanding the high-temperature superconductivity in cuprates. We report real space visualization of Mott transition in Sr1-xLaxCuO2+y cuprate films that cover the entire electron- and hole-doped regimes. Tunneling conductance measurements directly on the cooper-oxide (CuO2) planes reveal a systematic shift in the Fermi level, while the fundamental Mott-Hubbard band structure remains unchanged. This is further demonstrated by exploring atomic-scale electronic response of CuO2 to substitutional dopants and intrinsic defects in a sister compound Sr0.92Nd0.08CuO2. The results could be better explained in the framework of self-modulation doping, similar to that in semiconductor heterostructures, and form a basis for developing any microscopic theories for cuprate superconductivity.