Superconducting gap evolution in overdoped ${\mathrm{BaFe}}_2{\left({\mathrm{As}}_{1-x}{\mathrm{P}}_x\right)}_2$ single crystals through nanocalorimetry

Journal Article · Thu Jun 18 00:00:00 EDT 2015 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PhysRevB.91.245142· OSTI ID:1356616

Campanini, D.; Diao, Z.; Fang, L.; Kwok, W. -K.; Welp, U.; Rydh, A.

We report on specific heat measurements on clean overdoped BaFe₂(As_1-xP_x)₂ single crystals performed with a high resolution membrane-based nanocalorimeter. A nonzero residual electronic specific heat coefficient at zero temperature γ_r = C/T |_{T→ 0} is seen for all doping compositions, indicating a considerable fraction of the Fermi surface ungapped or having very deep minima. The remaining superconducting electronic specific heat is analyzed through a two-band s-wave alpha model in order to investigate the gap structure. Close to optimal doping we detect a single zero-temperature gap of Δ₀ ~ 5.3 meV, corresponding to Δ₀/k_BT_c ~ 2.2. Increasing the phosphorus concentration x, the main gap reduces till a value of Δ₀ ~ 1.9 meV for x = 0.55 and a second weaker gap becomes evident. From the magnetic field effect on γ_r, all samples however show similar behavior γ_r(H) $$-$$ γ_r (H = 0) ∝ to Hⁿ, with n between 0.6 and 0.7]. This indicates that, despite a considerable redistribution of the gap weights, the total degree of gap anisotropy does not change drastically with doping.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1356616
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 91, Issue 24; ISSN 1098-0121
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English