Shape resonances in multi-condensate granular superconductors formed by networks of nanoscale-striped puddles

TL;DR

This paper explores how shape resonances in multi-condensate granular superconductors, formed by nanoscale-striped puddles, influence superconducting gaps and critical temperature, revealing new mechanisms for gap enhancement and suppression.

Contribution

It demonstrates the formation of granular superconducting networks with shape resonances in high-Tc superconductors using scanning nano-X-ray diffraction.

Findings

Shape resonances cause gap suppression and amplification.

Granular networks form in high-temperature superconductors.

Maximum Tc occurs in scale-free superconducting networks.

Abstract

A characteristic feature of a superconductor made of multiple condensates is the possibility of the shape resonances in superconducting gaps. Shape resonances belong to class of Fano resonances in configuration interaction between open and closed scattering channels. The Shape resonances arise because of the exchange interaction, a Josephson-like term, for transfer of pairs between different condensates in different Fermi surface spots in the special cases where at least one Fermi surface is near a 2.5 Lifshitz topological transition. We show that tuning the shape resonances show first, the gap suppression (like a Fano anti-resonance) driven by configuration interaction between a BCS condensate and a BEC-like condensate, and second, the gap amplification (like a Fano resonance) driven by configuration interaction between BCS condensates in large and small Fermi surfaces. Shape resonances usually occur in granular nanoscale complex matter (called superstripes) because of the lattice instability near a 2.5 Lifshitz transition in presence of interactions. Using a new imaging method, scanning nano-X-ray diffraction, we have shown the generic formation in high temperature superconductors of a granular superconducting networks made of striped puddles formed by ordered oxygen interstitials or ordered local lattice distortions (like static short range charge density waves). In the superconducting puddles the chemical potential is tuned to a shape resonance in superconducting gaps and the maximum Tc occurs where the puddles form scale free superconducting networks.