Short-range symmetry breaking induced structural collapse and Tc enhancement in 122-type iron pnictide superconductors

TL;DR

This study explains how short-range symmetry breaking causes structural collapse and enhances Tc in 122-type iron pnictide superconductors, linking phase transition to increased superconducting temperature.

Contribution

It introduces a real-space effective c-axis lattice constant theory to analytically connect structural phase transitions with Tc enhancement in these materials.

Findings

Structural collapse due to symmetry breaking is linked to charge stripe lattice phase transition.

The phase transition can potentially raise Tc up to 80 K.

Analytical explanation aligns with experimental observations.

Abstract

In this paper, we investigate analytically the experimental observations of structural collapse and Tc enhancement in the rare earth-doped 122-type iron-based pnictide superconductors [S. R. Saha et.al. Phys. Rev. B 85, 024525 (2012), arXiv:1105.4798 (2011); B. Lv et al. PNAS 108, 15705 (2011).]. Based on the real-space effective c-axis lattice constant theory of superconductivity [X. Q. Huang, arXiv:1001.5067], it is shown that the abrupt c-axis reduction of the superconductors is due to the structural phase transition (an ultra-short-range symmetry breaking) of the charge stripe lattice. The existence of this phase transition corresponds to the change from the full-doped superconducting planes to the half-doped superconducting planes in the studied superconductors. It is estimated that this phase transition may help to promote the superconducting transition temperature of the 122 family up to as high as 80 K.