Orbital Ingredients and Persistent Dirac Surface State for the Topological Band Structure in FeTe0.55Se0.45

<a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msub><a:mi>FeTe</a:mi><a:mn>0.55</a:mn></a:msub><a:mrow><a:msub><a:mrow><a:mi>Se</a:mi></a:mrow><a:mrow><a:mn>0.45</a:mn></a:mrow></a:msub></a:mrow></a:math> (FTS) occupies a special spot in modern condensed matter physics at the intersections of electron correlation, topology, and unconventional superconductivity. The bulk electronic structure of FTS is predicted to be topologically nontrivial due to the band inversion between the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:msub><c:mi>d</c:mi><c:mrow><c:mi>x</c:mi><c:mi>z</c:mi></c:mrow></c:msub></c:math> and <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:msub><e:mi>p</e:mi><e:mi>z</e:mi></e:msub></e:math> bands along <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mrow><g:mi mathvariant="normal">Γ</g:mi><g:mtext>−</g:mtext><g:mi>Z</g:mi></g:mrow></g:math>. However, there remain debates in both the authenticity of the Dirac surface states (DSSs) and the experimental deviations of band structure from the theoretical band inversion picture. Here we resolve these debates through a comprehensive angle-resolved photoemission spectroscopy investigation. We first observe a persistent DSS independent of <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"><j:msub><j:mi>k</j:mi><j:mi>z</j:mi></j:msub></j:math>. Then, by comparing FTS with FeSe, which has no band inversion along <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"><l:mrow><l:mi mathvariant="normal">Γ</l:mi><l:mtext>−</l:mtext><l:mi>Z</l:mi></l:mrow></l:math>, we identify the spectral weight fingerprint of both the presence of the <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:msub><o:mi>p</o:mi><o:mi>z</o:mi></o:msub></o:math> band and the inversion between the <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:msub><q:mi>d</q:mi><q:mrow><q:mi>x</q:mi><q:mi>z</q:mi></q:mrow></q:msub></q:math> and <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"><s:msub><s:mi>p</s:mi><s:mi>z</s:mi></s:msub></s:math> bands. Furthermore, we propose a renormalization scheme for the band structure under the framework of a tight-binding model preserving crystal symmetry. Our results highlight the significant influence of correlation on modifying the band structure and make a strong case for the existence of topological band structure in this unconventional superconductor. Published by the American Physical Society 2024