The superconducting gap in the Hubbard model and the two gap energy scales in high-Tc cuprates

TL;DR

This paper uses a variational cluster approach to the 2D Hubbard model to explain the two distinct energy gaps observed in high-Tc cuprates, highlighting the role of spin fluctuations in pairing.

Contribution

It demonstrates that the Hubbard model can qualitatively reproduce the doping-dependent behavior of the two energy gaps in high-Tc superconductors, emphasizing spin fluctuations.

Findings

Antinodal gap increases with less doping.

Near-nodal gap decreases slightly with underdoping.

Spin fluctuations are crucial for pairing mechanism.

Abstract

Recent excperiments (ARPES, Raman) suggest the presence of two distinct energy gaps in high-Tc superconductors (HTSC), exhibiting different doping dependences. Results of a variational cluster approach to the superconducting state of the two-dimensional Hubbard model are presented which show that this model qualitatively describes this gap dichotomy: One gap (antinodal) increases with less doping, a behavior long considered as reflecting the general gap behavior of the HTSC. On the other hand, the near-nodal gap does even slightly decrease with underdoping. An explanation of this unexpected behavior is given which emphasizes the crucial role of spin fluctuations in the pairing mechanism.