Analysis of the diverging effective mass in YaBa2Cu3O6+x for high-Tc mechanism and pairing symmetry

Hyun-Tak Kim

doi:10.1142/s0217979218400313

Abstract

In order to clarify the high-T[Formula: see text] mechanism in inhomogeneous cuprate layer superconductors, we deduce and find the correlation strength which has not revealed before, contributing to the formation of the Cooper pair and the two-dimensional density of state, and demonstrate the pairing symmetry in the superconductors which is still controversial. To the open questions, the fitting and analysis of the diverging effective mass with decreasing doping, extracted from the acquired quantum-oscillation data in underdoped YaBa2Cu3O[Formula: see text] superconductors, using the extended Brinkman–Rice (BR) picture, reveal the nodal constant Fermi energy with the maximum carrier density, a constant Coulomb correlation strength [Formula: see text]=U/U[Formula: see text]0.90, and a growing Fermi arc from the nodal Fermi point to the isotropic Fermi surface with an increasing x. The growing of the Fermi arc indicates that a superconducting gap develops with x from the node (underdoped) to the anti-node (optimally or over-doped). The large [Formula: see text] results from the [Formula: see text]-wave metal–insulator transition for the pseudogap phase in lightly doped superconductors, which can be direct evidence for high-T[Formula: see text] superconductivity. The quantum critical point is regarded as the nodal Fermi point satisfied with the BR picture. The experimentally measured mass diverging behavior is an average effect and the true effective mass is constant. As an application of the nodal constant carrier density, the superconducting node gap analyzed by an angle-resolved photoemission spectroscopy (ARPES) is a precursor of s-wave symmetry in underdoped cuprates. Furthermore, the half-flux quantum, induced by the circulation of d-wave supercurrent and observed by the phase sensitive Josephson-[Formula: see text] junction experiments, is not shown due to “anisotropic or asymmetric effect” appearing in superconductors with trapped flux.

Highlights

Since the discovery of the high-Tc cuprate superconductor in 1986, numerous studies and theories have been presented.[1,2,3,4,5] the mechanism underlying high-Tc superconductivity has not been clarified because underdoped cuprate superconductors are highly inhomogeneous due to severe nonstoichiometry arising from strong oxygen disorder,[6,7] the critical or overdoped crystals are more homogeneous,[8,9] have a large continuous cylindrical Fermi surface,[10] and show s-wave symmetry.[11]
The magnitude of the node gap decreased with increasing doping concentration, which was observed in lightly doped cuprates.[33]
The gap anisotropy measured in an under-doped BSCCO showed that the pseudogap has d-wave symmetry.[13,15]

Summary

Introduction

Since the discovery of the high-Tc cuprate superconductor in 1986, numerous studies and theories have been presented.[1,2,3,4,5] the mechanism underlying high-Tc superconductivity has not been clarified because underdoped cuprate superconductors are highly inhomogeneous due to severe nonstoichiometry arising from strong oxygen disorder,[6,7] the critical or overdoped crystals are more homogeneous,[8,9] have a large continuous cylindrical Fermi surface,[10] and show s-wave symmetry.[11]. The Extended Brinkman-Rice Picture We briefly introduce the extended BR picture explaining the MIT as a two-phase model applied to an inhomogeneous system of a local metal region and an insulator region in the measurement region (black circle) [Fig. 1(a)].17,18,21 This model has two conditions: (1) a fractional effective charge e = ρe with band filling.

Fitting Idea and Fitting of the DEM Data

Correlation Strength κBR and Experimental Confirmation

Analysis of the Half-Flux-Quantum Image for Pairing Symmetry

Conclusion