Anomalous Band Bending in the (K $${}_{\mathbf{0.8}}$$ Na $${}_{\mathbf{0.2}}$$ ) $${}_{\mathbf{0.8}}$$ Fe $${}_{\mathbf{1.8}}$$ Se $${}_{\mathbf{2}}$$ Superconductor
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Abstract
Iron chalcogenides intercalated with alkali metal atoms attract the attention of physicists due to their unusual natural phase segregation, where superconducting clusters form at the boundaries of the antiferromagnetic phase. In this work, using photoelectron spectroscopy, we discovered an unusual effect that presumably arises due to this phase segregation. We studied temperature dependences of the photoelectron spectra of Se 3d, Fe 3p, and the valence band at temperatures above and below \(T_{c}\approx 27\) K of the compound (K\({}_{0.8}\)Na\({}_{0.2}\))\({}_{0.8}\)Fe\({}_{1.8}\)Se\({}_{2}\) with substitution of alkali metal atoms. A strong temperature dependence was found for both the valence band and the core levels: we observed a significant broadening of the spectra, which monotonically decreased with increasing sample temperature under cyclical temperature change. We believe that this broadening is associated with the appearance of volume charges in the dielectric matrix, leading to the band bending. Moreover, the shape of the potential that arises under the surface of this compound was restored, and an estimate was obtained for the relative amount of the superconducting phase. These results will help to better understand the physical processes occurring in this compound.
K $${}_{\mathbf{0.8}}$ Na $${}_{\mathbf{0.2}}$ 超导体中的反常带弯曲现象
摘要 与碱金属原子插层的铁铬化物因其不寻常的自然相分离而吸引了物理学家的注意，在反铁磁相的边界会形成超导簇。在这项研究中，我们利用光电子能谱发现了一种可能由这种相分离引起的不寻常效应。我们研究了化合物（K \({}_{0.8}\) Na \({}_{0.2}\) ）在高于和低于 \(T_{c}\approx 27\) K 的温度下 Se 3d、Fe 3p 和价带的光电子能谱的温度依赖性。\Fe \({}_{1.8}\) Se \({}_{2}\) 随着碱金属原子的替代。我们发现价带和核级都有很强的温度依赖性：我们观察到光谱有明显的展宽，在循环温度变化下，随着样品温度的升高，展宽单调地减小。我们认为，这种拓宽与介质基体中出现的体积电荷有关，导致了能带弯曲。此外，我们还还原了该化合物表面下产生的电势形状，并估算出了超导相的相对数量。这些结果将有助于更好地理解这种化合物中发生的物理过程。
期刊介绍：
Moscow University Physics Bulletin publishes original papers (reviews, articles, and brief communications) in the following fields of experimental and theoretical physics: theoretical and mathematical physics; physics of nuclei and elementary particles; radiophysics, electronics, acoustics; optics and spectroscopy; laser physics; condensed matter physics; chemical physics, physical kinetics, and plasma physics; biophysics and medical physics; astronomy, astrophysics, and cosmology; physics of the Earth’s, atmosphere, and hydrosphere.
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