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The effects of chemical substitutions with electron donors are thus particularly interesting to investigate. Here, we study the effect of Co substitution in the Fe site of CaKFe4As4 single crystals on the critical temperature, on the energy gaps, and on the superfluid density by using transport, point-contact Andreev-reflection spectroscopy (PCARS), and London penetration depth measurements. The pristine compound (Tc\u224336 K) shows two isotropic gaps whose amplitudes (\u03941 = 1.4\u20133.9 meV and \u03942 = 5.2\u20138.5 meV) are perfectly compatible with those reported in the literature. Upon Co doping (up to \u22487% Co), Tc decreases down to \u224320 K, the spin-vortex-crystal order appears, and the low-temperature superfluid density is gradually suppressed. PCARS and London penetration depth measurements perfectly agree in demonstrating that the nodeless multigap structure is robust upon Co doping, while the gap amplitudes decrease as a function of Tc in a linear way with almost constant values of the gap ratios 2\u0394i\/kBTc.<\/jats:p>","DOI":"10.3390\/nano14151319","type":"journal-article","created":{"date-parts":[[2024,8,5]],"date-time":"2024-08-05T18:21:40Z","timestamp":1722882100000},"page":"1319","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Superconductivity of Co-Doped CaKFe4As4 Investigated via Point-Contact Spectroscopy and London Penetration Depth Measurements"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-8733-5230","authenticated-orcid":false,"given":"Erik","family":"Piatti","sequence":"first","affiliation":[{"name":"Department of Applied Science and Technology, Politecnico di Torino, I-10129 Torino, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9551-1716","authenticated-orcid":false,"given":"Daniele","family":"Torsello","sequence":"additional","affiliation":[{"name":"Department of Applied Science and Technology, Politecnico di Torino, I-10129 Torino, Italy"},{"name":"Istituto Nazionale di Fisica Nucleare, Sezione di Torino, I-10125 Torino, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Francesca","family":"Breccia","sequence":"additional","affiliation":[{"name":"Department of Applied Science and Technology, Politecnico di Torino, I-10129 Torino, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1386-5762","authenticated-orcid":false,"given":"Tsuyoshi","family":"Tamegai","sequence":"additional","affiliation":[{"name":"Department of Applied Physics, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3368-1319","authenticated-orcid":false,"given":"Gianluca","family":"Ghigo","sequence":"additional","affiliation":[{"name":"Department of Applied Science and Technology, Politecnico di Torino, I-10129 Torino, Italy"},{"name":"Istituto Nazionale di Fisica Nucleare, Sezione di Torino, I-10125 Torino, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2180-7682","authenticated-orcid":false,"given":"Dario","family":"Daghero","sequence":"additional","affiliation":[{"name":"Department of Applied Science and Technology, Politecnico di Torino, I-10129 Torino, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2024,8,5]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"183","DOI":"10.1038\/nature08914","article-title":"Superconductivity gets an iron boost","volume":"464","author":"Mazin","year":"2010","journal-title":"Nature"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"645","DOI":"10.1038\/nphys1759","article-title":"High-temperature superconductivity in iron-based materials","volume":"6","author":"Paglione","year":"2010","journal-title":"Nat. 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