Boson-Fermion Duality and Metastability in Cuprate Superconductors

TL;DR

This paper explores how structural metastability and charge fluctuations in cuprate superconductors lead to a dual fermion-boson spectral structure, influencing Fermi surface behavior and pairing mechanisms.

Contribution

It introduces a model linking metastable domain structures to dual fermionic and bosonic spectral features in cuprates, highlighting their role in superconductivity.

Findings

Partial Fermi surface fractionation due to localized pairs.

Fermionic and bosonic spectral branches coexist in the single-particle spectrum.

Doping causes bound pairs to accumulate near anti-nodal points, affecting the gap.

Abstract

The intrinsic structural metastability in cuprate high T$_c$ materials, evidenced in a checker-board domain structure of the CuO$_2$ planes, locally breaks translational and rotational symmetry. Dynamical charge - deformation fluctuations of such nano-size unidirectional domains, involving Cu-O-Cu molecular bonds, result in resonantly fluctuating diamagnetic pairs embedded in a correlated Fermi liquid. As a consequence, the single-particle spectral properties acquire simultaneously (i) fermionic low energy Bogoliubov branches for propagating Cooper pairs and (ii) bosonic localized glassy structures for tightly bound states of them at high energies. The partial localization of the single-particle excitations results in a fractionation of the Fermi surface as the strength of the exchange coupling between itinerant fermions and partially localized fermion pairs increases upon moving from the nodal to the anti-nodal point. This is also the reason why, upon hole doping, bound fermion pairs predominantly accumulate near the anti-nodal points and ultimately condense in an anisotropic fashion, tracking the gap in the single particle spectrum.