32 research outputs found
Enhancement of vortex pinning in superconductor/ferromagnet bilayers via angled demagnetization
We use local and global magnetometry measurements to study the influence of
magnetic domain width w on the domain-induced vortex pinning in
superconducting/ferromagnetic bilayers, built of a Nb film and a ferromagnetic
Co/Pt multilayer with perpendicular magnetic anisotropy, with an insulating
layer to eliminate proximity effect. The quasi-periodic domain patterns with
different and systematically adjustable width w, as acquired by a special
demagnetization procedure, exert tunable vortex pinning on a superconducting
layer. The largest enhancement of vortex pinning, by a factor of more than 10,
occurs when w ~ 310 nm is close to the magnetic penetration depth.Comment: 5 pages, 3 figures, accepted to Phys. Rev. B, Rapid Communication
Effect of electron irradiation on superconductivity in single crystals of Ba(FeRu)As (0.24)
A single crystal of isovalently substituted Ba(FeRu)As
() was sequentially irradiated with 2.5 MeV electrons up to a maximum
dose of electrons/cm^2. The electrical resistivity was
measured \textit{in - situ} at 22 K during the irradiation and \textit{ex -
situ} as a function of temperature between subsequent irradiation runs. Upon
irradiation, the superconducting transition temperature, , decreases and
the residual resistivity, , increases. We find that electron
irradiation leads to the fastest suppression of compared to other types
of artificially introduced disorder, probably due to the strong short-range
potential of the point-like irradiation defects. A more detailed analysis
within a multiband scenario with variable scattering potential strength shows
that the observed vs. is fully compatible with pairing,
in contrast to earlier claims that this model leads to a too rapid a
suppression of with scattering
Tuning Vortex Confinement by Magnetic Domains in a Superconductor/Ferromagnet Bilayer
We use a line of miniature Hall sensors to study the effect of magnetic-domain-induced vortex confinement on the flux dynamics in a superconductor/ferromagnet bilayer. A single tunable bilayer is built of a ferromagnetic Co/Pt multilayer with perpendicular magnetic anisotropy and a superconducting Nb layer, with the insulating layer in-between to avoid the proximity effect. The magnetic-domain patterns of various geometries are reversibly predefined in the Co/Pt multilayer using the appropriate magnetization procedure. The magnetic-domain geometry strongly affects vortex dynamics, leading to geometry-dependent trapping of vortices at the sample edge, nonuniform flux penetration, and strongly nonuniform critical current density. With the decreasing temperature, the magnetic pinning increases, but this increase is substantially weaker than that of the intrinsic pinning. The analysis of the initial flux penetration suggests that vortices may form various vortex structures, including disordered Abrikosov lattice or single and double vortex chains, in which minimal vortex-vortex distance is comparable to the magnetic penetration depth
Anisotropy of the coherence length from critical currents in the stoichiometric superconductor LiFeAs
Miniature Hall-probe arrays were used to measure the critical current
densities for the three main directions of vortex motion in the stoichiometric
LiFeAs superconductor. These correspond to vortices oriented along the c-axis
moving parallel to the ab-plane, and to vortices in the ab-plane moving
perpendicular to, and within the plane, respectively. The measurements were
carried out in the low-field regime of strong vortex pinning, in which the
critical current anisotropy is solely determined by the coherence length
anisotropy parameter, {\epsilon}_{\xi}. This allows extraction of
{\epsilon}_{\xi} at magnetic fields far below the upper critical field B_c2. We
find that increasing magnetic field decreases the anisotropy of the coherence
length
Tuning Vortex Confinement by Magnetic Domains in a Superconductor/Ferromagnet Bilayer
We use a line of miniature Hall sensors to study the effect of magnetic-domain-induced vortex confinement on the flux dynamics in a superconductor/ferromagnet bilayer. A single tunable bilayer is built of a ferromagnetic Co/Pt multilayer with perpendicular magnetic anisotropy and a superconducting Nb layer, with the insulating layer in-between to avoid the proximity effect. The magnetic-domain patterns of various geometries are reversibly predefined in the Co/Pt multilayer using the appropriate magnetization procedure. The magnetic-domain geometry strongly affects vortex dynamics, leading to geometry-dependent trapping of vortices at the sample edge, nonuniform flux penetration, and strongly nonuniform critical current density. With the decreasing temperature, the magnetic pinning increases, but this increase is substantially weaker than that of the intrinsic pinning. The analysis of the initial flux penetration suggests that vortices may form various vortex structures, including disordered Abrikosov lattice or single and double vortex chains, in which minimal vortex-vortex distance is comparable to the magnetic penetration depth
Effect of Electron Irradiation on Superconductivity in Single Crystals of Ba(Fe1−xRux)2As2 (x=0.24)
A single crystal of isovalently substituted Ba(Fe1−xRux)2As2 (x=0.24) is sequentially irradiated with 2.5 MeV electrons up to a maximum dose of 2.1×1019 e−/cm2. The electrical resistivity is measuredin situ at T=22 K during the irradiation and ex situ as a function of temperature between subsequent irradiation runs. Upon irradiation, the superconducting transition temperature Tc decreases and the residual resistivity ρ0 increases. We find that electron irradiation leads to the fastest suppression of Tccompared to other types of artificially introduced disorder, probably due to the strong short-range potential of the pointlike irradiation defects. A more detailed analysis within a multiband scenario with variable scattering potential strength shows that the observed Tc versus ρ0 is fully compatible with s±pairing, in contrast to earlier claims that this model leads to a too rapid suppression of Tc with scattering
Electron irradiation effects on superconductivity in PdTe: an application of a generalized Anderson theorem
Low temperature ( 20~K) electron irradiation with 2.5 MeV relativistic
electrons was used to study the effect of controlled non-magnetic disorder on
the normal and superconducting properties of the type-II Dirac semimetal
PdTe. We report measurements of longitudinal and Hall resistivity, thermal
conductivity and London penetration depth using tunnel-diode resonator
technique for various irradiation doses. The normal state electrical
resistivity follows Matthiessen rule with an increase of the residual
resistivity at a rate of 0.77cm/. London penetration depth and thermal
conductivity results show that the superconducting state remains fully gapped.
The superconducting transition temperature is suppressed at a non-zero rate
that is about sixteen times slower than described by the Abrikosov-Gor'kov
dependence, applicable to magnetic impurity scattering in isotropic,
single-band -wave superconductors. To gain information about the gap
structure and symmetry of the pairing state, we perform a detailed analysis of
these experimental results based on insight from a generalized Anderson theorem
for multi-band superconductors. This imposes quantitative constraints on the
gap anisotropies for each of the possible pairing candidate states. We conclude
that the most likely pairing candidate is an unconventional
state. While we cannot exclude the conventional and the triplet
, we demonstrate that these states require additional assumptions about
the orbital structure of the disorder potential to be consistent with our
experimental results, e.g., a ratio of inter- to intra-band scattering for the
singlet state significantly larger than one. Due to the generality of our
theoretical framework, we think that it will also be useful for irradiation
studies in other spin-orbit-coupled multi-orbital systems.Comment: 22 pages, 12 figure
Unconventional nodal superconductivity in miassite RhS
Unconventional superconductivity has long been believed to arise from a
lab-grown correlated electronic system. Here we report compelling evidence of
unconventional nodal superconductivity in a mineral superconductor \rhs. We
investigated the temperature-dependent London penetration depth
and disorder evolution of the critical temperature and
upper critical field in synthetic miassite \rhs. We found a
power-law behavior of with at low
temperatures below ( = 5.4 K), which is consistent with the
presence of lines of the node in the superconducting gap of \rhs. The nodal
character of the superconducting state in \rhs~was supported by the observed
pairbreaking effect in and in samples with the controlled
disorder that was introduced by low-temperature electron irradiation. We
propose a nodal sign-changing superconducting gap in the irreducible
representation, which preserves the cubic symmetry of the crystal and is in
excellent agreement with the superfluid density,
Vortex Dynamics in Ferromagnetic/Superconducting Bilayers
The dependence of vortex dynamics on the geometry of magnetic domain pattern is studied in the superconducting/ferromagnetic bilayers, in which niobium is a superconductor, and Co/Pt multilayer with perpendicular magnetic anisotropy serves as a ferrromagnetic layer. Magnetic domain patterns with different density of domains per surface area and different domain size, w, are obtained for Co/Pt with different thickness of Pt. The dense patterns of domains with the size comparable to the magnetic penetration depth (w≥λ) produce large vortex pinning and smooth vortex penetration, while less dense patterns with larger domains (w ≫ λ) enhance pinning less effectively and result in flux jumps during flux motion