Decoding 122-type iron-based superconductors: A comprehensive simulation of phase diagrams and transition temperatures

Abstract

Iron-based superconductors, a cornerstone of low-temperature physics, have been the subject of numerous theoretical models aimed at deciphering their complex behavior. In this study, we present a comprehensive approach that amalgamates several existing models and incorporates experimental data to simulate the superconducting phase diagrams of the principal “122-type” iron-based compounds. Our model considers a multitude of factors including the momentum dependence of the superconducting gap, spin-orbital coupling, antiferromagnetism, spin-density wave, induced <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mi mathvariant="italic">XY</a:mi></a:mrow></a:math> potential on the tetrahedral structure, and electron-phonon coupling. We have refined the electron-phonon scattering matrix using experimental angle-resolved photoemission spectroscopy data, ensuring that relevant electrons pertinent to iron-based superconductivity are accounted for. This innovative approach allows us to calculate theoretical critical temperature <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mo>(</c:mo><c:msub><c:mi>T</c:mi><c:mi mathvariant="normal">c</c:mi></c:msub><c:mo>)</c:mo></c:math> values for <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mrow><e:msub><e:mi>Ba</e:mi><e:mrow><e:mn>1</e:mn><e:mo>−</e:mo><e:mi>x</e:mi></e:mrow></e:msub><e:msub><e:mi mathvariant="normal">K</e:mi><e:mi>x</e:mi></e:msub><e:msub><e:mi>Fe</e:mi><e:mn>2</e:mn></e:msub><e:msub><e:mi>As</e:mi><e:mn>2</e:mn></e:msub></e:mrow><e:mo>,</e:mo><e:mo> </e:mo><e:mrow><e:mi>Ca</e:mi><e:msub><e:mi>Fe</e:mi><e:mn>2</e:mn></e:msub><e:msub><e:mi>As</e:mi><e:mn>2</e:mn></e:msub></e:mrow></e:math>, and <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:mrow><g:mi>Sr</g:mi><g:msub><g:mi>Fe</g:mi><g:mn>2</g:mn></g:msub><g:msub><g:mi>As</g:mi><g:mn>2</g:mn></g:msub></g:mrow></g:math> as functions of pressure. These calculated values exhibit remarkable agreement with experimental findings. Furthermore, our model predicts that <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"><h:mrow><h:mi>Mg</h:mi><h:msub><h:mi>Fe</h:mi><h:mn>2</h:mn></h:msub><h:msub><h:mi>As</h:mi><h:mn>2</h:mn></h:msub></h:mrow></h:math> remains nonsuperconducting irrespective of the applied pressure. Given that 122-type superconductivity at low pressure or low doping concentration has been experimentally validated, our work serves as a powerful predictive tool for generating superconducting phase diagrams at high pressure empirically. This study underscores that the high transition temperatures and the precise doping and pressure dependence of iron-based superconductors are intrinsically linked to an intertwined mechanism involving a strong interplay between structural, magnetic, and electronic degrees of freedom. Published by the American Physical Society 2024

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