Multigap superconductivity in RbCa₂Fe₄As₄F₂ investigated using μSR measurements

The superconducting properties of the recently discovered high-T_c superconductor RbCa₂Fe₄As₄F₂ with double Fe₂As₂ layers and T_c ≈ 30 K have been investigated using magnetization, heat capacity, transverse-field (TF) and zero-field (ZF) muon-spin rotation/relaxation (μSR) measurements. Low field magnetization and heat capacity (C_p) measurements reveal an onset of bulk superconductivity with T_c ∼ 30.0(4) K, where there is a jump at T_c of ΔC_p/T_c = 94.6 (mJ/mole-K²). The temperature dependence of the magnetic penetration depth obtained from transverse-field (TF) μSR is better described by the two-gap s + s and s + d models than the single gap s- or d-wave scenarios. The presence of two superconducting gaps in RbCa₂Fe₄As₄F₂ is consistent with the multigap superconductivity observed in other Fe-based superconductors, including ACa₂Fe₄As₄F₂ (A = K and Cs). >From the TF-μSR study, an in-plane magnetic penetration depth of λ_ab(0) = 231.5(3) nm, a superconducting carrier density n_s = 1.29(1) × 10²⁷ m⁻³, and an effective mass of the carriers of m* = 2.45(1)m_e are estimated. Zero-field μSR measurements do not reveal clear signs of time reversal symmetry breaking below T_c, but the temperature dependence of the relaxation of the asymmetry between 150 and 1.2 K may indicate the presence of spin-fluctuations. (author)