We report the observation of half-integer magnetic flux quantization in mesoscopic rings of superconducting β-Bi 2 Pd thin films. The half-quantum fluxoid manifests itself as a π phase shift in the quantum oscillation of the critical temperature. This result verifies unconventional superconductivity of β-Bi 2 Pd, in accord with the expectation of a topological superconductor. We also discuss the strong indication that β-Bi 2 Pd is a spin-triplet superconductor. The condensation of Cooper pairs gives rise to superconductivity [1]. A key signature of the electron pairing is the quantization of the magnetic flux through a multiply-connected superconducting body, in discrete units of Φ 0 = hc 2e. Indeed, the observations of the fluxoid quantization served as the first experimental verifications of the BCS theory [2, 3, 4]. Shortly after the initial magnetometry measurements, Little and Parks further demonstrated the oscillatory feature of the superconducting transition temperature T c , as a result of the periodic free energy of the superconducting state as a function of the applied magnetic flux [5]. The minimumof the free energy, or the maximum of the T c , is always achieved when the applied magnetic flux takes Φ = nΦ 0 , where n is an integer number. In the following decades, the Little-Parks effect, as a stringent test for the electron pairing, has been observed in numerous superconducting materials [6,7,8,9]. On the other hand, Geshkenbein, Larkin and Barone (GLB) predicted that

In this work, the different coupling strengths of Fe-octaethylporphyrin molecules sublimated in situ onto epitaxially grown Co and Ni films on Cu͑100͒ are studied by systematic x-ray-absorption and x-ray magnetic circular dichroism ͑XMCD͒ measurements. The fine structures observed in the absorption and dichroic spectra of the Fe-L 2,3 edges are explained in terms of different Fe 3d orbitals probed in angular-dependent measurements. The coverage of Fe-porphyrin molecules is varied from submonolayer to 1.5 ML ͑monolayer͒, and measurements were carried out at room as well as at low temperatures. From the temperature dependence of the Fe-XMCD signal, a weaker coupling strength between the Fe atom and the Ni substrate is found as compared to the Co case.

A prime category of superconducting materials in which to look for spin-triplet pairing and topological superconductivity are superconductors without inversion symmetry. It is predicted that the breaking of parity symmetry gives rise to an admixture of spin-singlet / spin-triplet pairing states; a triplet pairing component, being substantial, seems all but guaranteed. However, the experimental confirmation of pair mixing in any particular material remains elusive. In this work, we perform phase-sensitive experiment to examine the pairing state of noncentrosymmetric superconductor α−BiPd. The Little-Parks effect observed in mesoscopic polycrystalline α−BiPd ring devices reveals the presence of half-integer magnetic flux quantization, which provides a decisive evidence for the spin-triplet pairing state. We find mixed half-quantum fluxes and integer-quantum fluxes, consistent with the scenario of singlet-triplet pair mixing.

Ultrathin Ni/ Cu/ Co trilayers were deposited in ultrahigh vacuum and the ferromagnetic resonance measured in situ as a function of both, temperature and out-of-plane angle of the external field. The interlayer exchange coupling J inter was then unambiguously extracted at various temperatures, entirely from the angular dependence of the resonance field positions. The temperature dependence of J inter ͑T͒ follows an effective power law AT n , n Ϸ 1.5. Analysis of the scaling parameter A shows an oscillatory behavior with spacer thickness, as does the strength of the coupling at T = 0. The results clearly indicate that the dominant contribution to J inter ͑T͒ is due to the excitation of thermal spin waves and follows recently developed theory closely.

Single crystalline body-centered-cubic ͑bcc͒ Co films were achieved on FeCu 3 buffer layer by molecularbeam epitaxy. Fourfold symmetric magnetic hysteresis loops for bcc Co were obtained unambiguously with the easy axes along Co͗110͘. The in-plane uniaxial anisotropy is significantly reduced by FeCu 3 buffer layer. The magnetocrystalline anisotropy constant of bcc Co was further determined to be −1.0ϫ 10 5 erg/ cm 3 by rotational-magneto-optical Kerr effect. Hexagonal-close-packed Co, which would contribute an effective positive K 1 , appeared on top of bcc Co when the film thickness was beyond 0.9 nm. As a result, the magnetocrystalline anisotropy constant of the whole system switched from negative to positive with increasing film thickness.