Pseudogap, Superconducting Gap, and Fermi Arc in High-Tc Cuprates Revealed by Angle-Resolved Photoemission Spectroscopy

TL;DR

This paper reviews ARPES studies on high-Tc cuprates, revealing the complex relationship between pseudogap, superconducting gap, and Fermi arc, highlighting multiple energy scales and their material and doping dependencies.

Contribution

It provides a comprehensive overview of ARPES findings on the momentum-dependent energy gaps and introduces the concept of an effective superconducting gap related to Tc.

Findings

Identification of two distinct energy scales, Delta_0 and Delta^*.

Material independence of Delta^* at fixed doping.

Correlation of the effective gap Delta_sc with Tc.

Abstract

We present an overview of angle-resolved photoemission spectroscopy (ARPES) studies of high-temperature cuprate superconductors aiming at elucidating the relationship between the superconductivity, the pseudogap, and the Fermi arc. ARPES studies of underdoped samples show a momentum dependence of the energy gap below Tc which deviates from a simple d-wave form, suggesting the coexistence of multiple energy scales in the superconducting state. Hence, two distinct energy scales have been introduced, namely, the gap near the node (characterized by Delta_0) and in the anti-nodal region (characterized by Delta^*). Dichotomy between them has been demonstrated from the material, doping, and temperature dependence of the energy gap. While Delta^* at the same doping level is approximately material independent, Delta_0 shows a strong material dependence tracking the magnitude of Tc,max. The anti-nodal gap does not close at Tc in contrast to the gap near the node which follows something closer to a BCS-like temperature dependence. An effective superconducting gap Delta_sc defined at the end point of the Fermi arc is found to be proportional to Tc's in various materials.