The FeSe nematic phase has been the focus of recent research on iron-based superconductors (IBSs) due to its unusual properties, which are distinct from those of the pnictides. A series of theoretical/experimental studies were performed to determine the origin of the nematic phase. However, they yielded conflicting results and caused additional controversies. Here, we report the results of angle-resolved photoemission and X-ray absorption spectroscopy studies on FeSe detwinned by a piezo stack. We fully resolved band dispersions with orbital characters near the Brillouin zone (BZ) corner, and revealed an absence of any Fermi pocket at the Y point in the 1-Fe BZ. In addition, the occupation imbalance between \({d}_{{xz}}\) and \({d}_{{yz}}\) orbitals was the opposite of that of iron pnictides, consistent with the identified band characters. These results resolve issues associated with the FeSe nematic phase and shed light on the origin of the nematic phase in IBSs.

FeSe向列相一直是铁基超导体（IBSs）的最新研究热点，因为它的非同寻常的特性与pnictides不同。进行了一系列的理论/实验研究，以确定向列相的起源。但是，它们产生了矛盾的结果，并引起了更多争议。在这里，我们报告对压电叠层纠缠的FeSe进行角分辨光发射和X射线吸收光谱研究的结果。我们完全解决了布里渊区（BZ）拐角附近具有轨道特征的带色散问题，并揭示了1-Fe BZ的Y点处没有费米腔。此外，\（{d} _ {{xz}} \）和\（{d} _ {{yz}} \）之间的职业失衡轨道与铁肽相反，与确定的谱带特征一致。这些结果解决了与FeSe向列相有关的问题，并阐明了IBS中​​向列相的起源。