Doping-evolution of the superconducting gap in single crystals of (Ca _1-x La _x ) ₁₀ (Pt ₃ As ₈ )(Fe ₂ As ₂ ) ₅ superconductor from London penetration depth measurements

Journal Article · Fri Sep 19 04:00:00 EDT 2014 · Superconductor Science and Technology

DOI:https://doi.org/10.1088/0953-2048/27/10/104006· OSTI ID:1233279

Cho, K.; Tanatar, M. A.; Ni, N.; Prozorov, R.

The doping-evolution of the superconducting gap structure in iron-based superconductor (Ca^{1-xLa_x)₁₀(Pt₃As₈)(Fe₂As₂)₅(x = 0.04, 0.06, 0.09, 0.11, and 0.18) was probed by high-resolution measurements of the London penetration depth, λ(T). The samples spanned compositions from underdoped to slightly overdoped with superconducting critical temperatures, T_c, from 12.7 K (x = 0.04) through (optimal) 23.3 K (x = 0.11) to 21.9 K (x = 0.18). The low-temperature variation (up to 0.3 T_c ) of λ(T) was analysed using a power-law function, Δλ = AT_n. For compositions close to the optimal doping, (x = 0.09, 0.11, and 0.18), characterized by T_c > 20K, Δλ(T) shows a tendency to saturation, indicative of a full gap on the Fermi surface. Fitting over the lowest temperature range (T < 0.1 T_c) gives n = 2.6. This value is well outside the range 1 ≤ n ≤ 2 expected for the line-nodal superconductor. The exponent n decreased to n ~ 2 in the two most underdoped compositions x = 0.04 (T_c = 12.7 K) and 0.06 (T_c = 18.2 K), implying the development of a notable gap anisotropy revealed by the enhanced influence of pair-breaking scattering. This decrease is accompanied by a significant increase of the total variation of the penetration depth Δλ in a fixed temperature interval (e.g., T_min - 0.3T_c). Both the decrease of the exponent and the increase of the absolute value of Δλ in the underdoped regime are similar to the observations in other charge-doped iron-based superconductors, such as doped BaFe₂As₂ and NaFeAs, suggesting a universal behavior in iron-based superconductors.}

• Research Organization: Ames Laboratory (AMES), Ames, IA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC02-07CH11358
• OSTI ID: 1233279
• Report Number(s): IS-J 8556
• Journal Information: Superconductor Science and Technology, Journal Name: Superconductor Science and Technology Journal Issue: 10 Vol. 27; ISSN 0953-2048
• Publisher: IOP Publishing
• Country of Publication: United States
• Language: English