Doping induced electronic phase separation and coulomb bubbles in layered superconductors

TL;DR

This paper explores how doping causes electronic phase separation and Coulomb bubble formation in layered superconductors, leading to a transition from superconducting to insulating states through charge clustering and percolation.

Contribution

It introduces a microscopic model describing Coulomb bubble formation and their role in the insulator transition in layered superconductors, supported by experimental correlations.

Findings

Coulomb bubbles form at low densities, trapping charge carriers.

Insulating state arises via percolation of Coulomb bubbles.

Model aligns with experimental data from transport and STM studies.

Abstract

We have studied properties of quantum charge fluids interacting with random impurities or heavy polarons using a microscopic Hamiltonian with the full many-body Coulomb interaction with the use of variational many-body formalism. At zero temperature and high enough density the bosonic fluid is superconducting, but when density decreases the Coulomb interaction will be strongly over-screened and impurities or polarons begin to trap charge carriers forming bound quasiparticle like clusters, which we call Coulomb bubbles or clumps. These bubbles are embedded inside the superconductor and form nuclei of a new insulating state- the local Charge Density Wave(CDW). The growth of a bubble is terminated by the Coulomb force. The fluid contains two groups of charge carriers associated with free and localized states. The insulating state arises via a percolation of the insulating islands of bubbles, which cluster and prevent the flow of the electrical supercurrent through the system. The picture is consistent with the Gorkov and Teitelbaum (GT) analysis of the transport, Hall effect data and the ARPES spectra as well as with nanoscale superstructures observed in Scanning Tunneling Microscope(STM) experiments. The scenario of the clump formation may be also applicable to pnictides, where two types of clumps may arise even at very high temperatures. The paper has been published in the book "Condensed Matter Theories" volume 24.