Transport, magnetic and optical investigations on EuRbFe 4 As 4 single crystals evidence that the ferromagnetic ordering of the Eu 2+ magnetic moments at T N = 15 K, below the superconducting transition (Tc = 36 K), affects superconductivity in a weak but intriguing way. Upon cooling below T N , the zero resistance state is preserved and the superconductivity is affected by the in-plane ferromagnetism mainly at domain boundaries; a perfect diamagnetism is recovered at low temperatures. The infrared conductivity is strongly suppressed in the far-infrared region below Tc, associated with the opening of a complete superconducting gap at 2∆ = 10 meV. A gap smaller than the weak coupling limit suggests the strong orbital effects or, within a multiband superconductivity scenario, the existence of a larger yet unrevealed gap.New members of the iron-pnictide family, the so-called 1144-compounds, attract interest recently because the alternating layers of alkaline A and alkaline-earth B cations produce two different kinds of As sites [1][2][3][4]. These materials can be viewed as the intergrowth of A-122 and B-122 iron-pnictides and they are naturally hole doped. The parent compounds are superconducting with transition temperatures T c around 35 K, higher than most of the 122materials; no spin-density-wave order has been observed. Among all possible candidates, Eu-based 1144-systems are even more intriguing, since the Eu-sublattice orders ferromagnetically below a critical temperature T N ≈ 15 K [5,6], similar to the 122-counterpart EuFe 2 As 2 [7-11]. Ferromagnetic order deep inside the superconducting state is very rare, in general [12,13]; hence the "ferromagnetic superconductor" EuRbFe 4 As 4 might pave the way towards realization of a "superconducting ferromagnet" [14-16]. However, the exact nature of the Eu magnetic order and its effect on superconductivity is unresolved [5, 6] because single crystals have been synthesized only recently.In this Letter we focus on the interplay between superconductivity and ferromagnetism in EuRbFe 4 As 4 single crystals. We report comprehensive investigations comprising transport, magnetic and optical measurements combined with microscopic studies of the vortex dynamics. The infrared spectra show a clear gap opening around 80 cm −1 below T c = 36 K that is slightly reduced compared to the value expected from the BCS theory. We relate this small value to the multiband character of superconductivity as well as to the depairing (orbital) effects of super-currents screening the ferromagnetic domains. A surprisingly weak effect on the superconducting condensate has been observed upon magnetic ordering indicating a rather weak interaction between Eu-and Fe-sublattices.Single crystals of EuRbFe 4 As 4 are obtained according to Ref. [4,5,17,18]; they exhibit shiny ab-faces of approximately 1 mm in size. The structure of the compound is presented in Fig. 1(a). The crystals are characterized by x-ray, electrical transport, and magnetic susceptibility measurements. In Fig. 1(a) we plot the dc ...

We report comprehensive study of physical properties of the binary superconductor compound SnAs. The electronic band structure of SnAs was investigated using both angle-resolved photoemission spectroscopy (ARPES) in a wide binding energy range and density functional theory (DFT) within generalized gradient approximation (GGA). The DFT/GGA calculations were done including spin-orbit coupling for both bulk and (111) slab crystal structures. Comparison of the DFT/GGA band dispersions with ARPES data shows that (111) slab much better describes ARPES data than just bulk bands. Superconducting properties of SnAs were studied experimentally by specific heat, magnetic susceptibility, magnetotransport measurements and Andreev reflection spectroscopy. Temperature dependences of the superconducting gap and of the specific heat were found to be well consistent with those expected for the single band BCS superconductors with an isotropic s-wave order parameter. Despite spin-orbit coupling is present in SnAs, our data shows no signatures of a potential unconventional superconductivity, and the characteristic BCS ratio 2∆/Tc = 3.48 − 3.73 is very close to the BCS value in the weak coupling limit.

We discuss the synthesis, characterization, and comprehensive study of Ba-122 single crystals with various substitutions and various superconducting transition temperatures. We use five complementary techniques to obtain a self-consistent set of data on the superconducting properties of Ba-122. A major conclusion of our work is the coexistence of two superconducting condensates differing in the electron–boson coupling strength. The two gaps that develop in distinct Fermi surface sheets are nodeless in the kxky plane and exhibit s-wave symmetry; the two-band model suffices for the description of the main parameters of the superconducting state. A moderate interband coupling and a considerable Coulomb repulsion in the description of the two-gap superconducting state of barium pnictides favor the s++ model.

Using wideband (0.5–6.5 eV) spectroscopic ellipsometry, we study ultrathin [Bi(0.6–2.5 nm)–FeNi(0.8,1.2 nm)]N multilayer films grown by rf sputtering deposition, where the FeNi layer has a nanoisland structure and its morphology and magnetic properties change with decreasing the nominal layer thickness. From multilayer model simulations of the ellipsometric angles, Ψ(ω) and Δ(ω), complex (pseudo)dielectric function spectra of the Bi layer were extracted. The obtained results demonstrate that the Bi layer can possess the surface metallic conductivity, which is strongly affected by the morphology and magnetic properties of the nanoisland FeNi layer in GMR-type Bi–FeNi multilayer structures.

In a superconductor that lacks inversion symmetry, the spatial part of the Cooper pair wave function has a reduced symmetry, allowing for the mixing of spin-singlet and spin-triplet Cooper pairing channels and thus providing a pathway to a non-trivial superconducting state. Materials with a non-centrosymmetric crystal structure and with strong spin–orbit coupling are a platform to realize these possibilities. Here, we report the synthesis and characterisation of high quality crystals of Sn4As3, with non-centrosymmetric unit cell (R3m). We have characterised the normal and superconducting states using a range of methods. Angle-resolved photoemission spectroscopy shows a multiband Fermi surface and the presence of two surface states, confirmed by density-functional theory calculations. Specific heat measurements reveal a superconducting critical temperature of T c ∼ 1.14 K and an upper critical magnetic field of μ 0 H c ≳ 7 mT, which are both confirmed by ultra-low temperature scanning tunneling microscopy and spectroscopy. Scanning tunneling spectroscopy shows a fully formed superconducting gap, consistent with conventional s-wave superconductivity.