Superconducting Gap Structures and Interband Fluctuations in Electron-Doped Pnictide Sr0.85La0.15Fe2As2 Single Crystals

International Journal of Physics | Vol. 16, No. 6, June 2025 | pp. 41–48

DOI: 10.46882/2025/IJP/000182

Research Article

Title: Superconducting Gap Structures and Interband Fluctuations in Electron-Doped Pnictide Sr0.85La0.15Fe2As2 Single Crystals

Names of Authors: I. R. Sokolov¹, V. I. Morozov²

Authors’ Affiliations:
¹ Kapitza Institute for Physical Problems, Russian Academy of Sciences, Moscow, Russia
² Institute of High Pressure Physics, Russian Academy of Sciences, Troitsk, Russia

Abstract: Establishing the exact pairing symmetries of iron-based pnictide superconductors remains a primary objective within modern solid-state and condensed matter physics pipelines. We synthesized high-quality single crystals of electron-doped Sr0.85La0.15Fe2As2 using a specialized self-flux crystal growth routine under high-pressure configurations. The internal superconducting gap structures and spin fluctuations were evaluated using high-resolution angle-resolved photoemission spectroscopy and low-temperature London penetration depth tracking. The single crystals displayed a sharp superconducting transition at Tc = 26.0 K with an exceptionally narrow magnetic susceptibility transition width of ΔT = 0.3 K. The temperature dependence of the London penetration depth exhibits an exponential profile at low operational targets (T less than 0.3 Tc), ruling out the existence of line nodes across the order parameter. The photoemission mapping revealed two distinct, fully gapped isotropic superconducting bands across the Fermi surface. The large gap magnitude was measured at Δ1 = 7.1 meV on the inner hole-like sheet, while the lower gap registered at Δ2 = 3.5 meV on the outer electron-like sheets. This structure yields a strong-coupling index of 2Δ1/kBTc = 6.3, verifying strong-coupling pairing driven by interband spin fluctuations.

Keywords: Iron-based superconductors; gap structures; photoemission spectroscopy; London penetration depth; pairing symmetry; spin fluctuations

Manuscript Timeline: Received: March 02, 2025; Revised: April 14, 2025; Accepted: May 02, 2025; Published: June 18, 2025

Citation: Sokolov, I. R., & Morozov, V. I. (2025). Superconducting Gap Structures and Interband Fluctuations in Electron-Doped Pnictide Sr0.85La0.15Fe2As2 Single Crystals. International Journal of Physics, 16(6), 41–48.

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