2025/11/13 by Chih-Han Wang, Wang, Chih-Han, Weiyin Ma +8
Materials Science · Physics and Astronomy · #FOS: Physical sciences #Iron-based superconductors research #Organic and Molecular Conductors Research #Physics of Superconductivity and Magnetism #Superconductivity (cond-mat.supr-con)
paper · pdf · doi:10.48550/arxiv.2511.10443
openalex publication_date 2025/11/13 · openalex created_date 2025/11/15 · openalex updated_date 2026/07/28
The origin of the four-fold Tc amplification in AxFe2-ySe2 (>30 K) compared to FeSe (8 K) remains a central puzzle, complicated by a debate over the true superconducting (SC) parent phase--the I4/m (245) insulating matrix or a supposed I4/mmm metallic phase. Here, we resolve this ambiguity by identifying a novel "stripe-type orthorhombic phase" as the true parent phase of the high-Tc state, whose diffraction signature is the d2 peaks. Through decisive experiments, we demonstrate that this d2 parent phase is not intrinsically superconducting. Instead, superconductivity emerges only after this stripe phase undergoes a subsequent structural distortion, the definitive signature of which is the asymmetric broadening of the d1 main peaks. Our findings establish that the d2 peaks signal the formation of the parent phase, while the broadening of d1 peaks signals the transition into the superconducting state. This discovery of a two-step transition--formation of a stripe parent phase, followed by a superconducting distortion--provides a new mechanism for Tc amplification via controlled heterogeneity.