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TT: Fachverband Tiefe Temperaturen

TT 95: Fe-based Superconductors

TT 95.1: Talk

Friday, March 13, 2026, 09:30–09:45, HSZ/0103

Saddle-point-nesting driven formation of charge order and superconducting vortex splitting on heavily hole-doped iron-arsenide superconductors — •Chi Ming Yim — Tsung-Dao Lee Institute & School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China

The study of iron-arsenide superconductor Ba_1−xK_xFe₂As₂ (BKFA) has re-sparked considerable interest following the recent discoveries in this material of superconductivity with broken time-reversal symmetry [1], superconducting vortices with fractional flux quantum [2], and quartic states [3]. Most studies focus on its bulk properties, with much less attention paid to its surface(s). This talk reports on our recent STM/S findings on the surfaces of BKFA in its heavily-hole doped regime: On the As- surface of BKFA (x=0.77), we observe of a density wave order with a 2x2 spatial periodicity, with clear-cut evidence(s) confirming its charge origin. Our calculation results indicate that its formation is saddle-point nesting driven. [4]. On the K- surface of multiband superconductor KFe₂As₂ studied under an external magnetic field, we observe splitting of vortices with integer flux quantum into those with appreciably reduced conductance, demonstrating the possibility of vortex core fractionalization in a multiband superconductor [5].
[1] Grinenko et al., Nat. Phys. 17, 1254 (2021)
[2] Iguchi et al., Science 380, 1244 (2023)
[3] Shipulin et al., Nat. Commun. 14, 6734 (2023)
[4] Hu et al., Nat. Commun. 18, 253 (2025)
[5] Zheng et al., Arxiv 2407.18610 (2024)

Keywords: iron-based superconductors; superconductivity; charge density order; scanning tunnneling microscopy and spectroscopy