Model for the occurrence of Fermi pockets without the pseudogap hypothesis in underdoped cuprate superconductors - Interplay of Jahn-Teller physics and Mott physics -

TL;DR

This paper presents a model explaining Fermi pockets in underdoped cuprates without invoking a pseudogap, emphasizing the roles of Jahn-Teller and Mott physics in shaping electronic structures and ARPES features.

Contribution

It introduces a model based on Jahn-Teller and Mott physics that accounts for Fermi pockets and ARPES observations without requiring a pseudogap hypothesis.

Findings

Fermi pockets are formed by doped holes coexisting with local antiferromagnetic order.

Below Tc, holes form d-wave Cooper pairs in the nodal region.

No pseudogap exists in the antinodal region according to the model.

Abstract

Central issues in the electronic structure of underdoped cuprate superconductors are to clarify the shape of the Fermi surfaces and the origin of a pseudogap. Based on the model proposed by Kamimura and Suwa which bears important characteristics born from the interplay of Jahn-Teller Physics and Mott Physics, we show that the feature of Fermi surfaces is the Fermi pockets constructed by doped holes under the coexistence of a metallic state and of the local antiferromagnetic order. Below $T_{\rm c}$ the holes on Fermi pockets form Cooper pairs with d-wave symmetry in the nodal region. In the antinodal region all the states below the Fermi level are occupied by electrons so that there is no gap, not even pseudo both below and above $T_{\rm c}$. Calculated angle-resolved photoemission spectrum below $T_{\rm c}$ show a coherent peak at the nodal region while a broad hump in antinodal region. From this feature the origin of the two distinct gaps in observed ARPES is elucidated. The finite-size-effects of a spin-correlation length coexisting with a metallic state are discussed. In particular, we discuss a possibility of the spatially inhomogeneous distribution of Fermi-pocket-states and of large-Fermi-surface-states above $T_{\rm c}$ which changes with time. Finally a new phase diagram for underdoped cuprates is proposed.