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Register a new userEffect of Heavy-Ion Irradiation on Superconductivity in Single Crystals of Ba0.6K0.4Fe2As2 Pnictide Superconductor
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The London penetration depth was measured in optimally doped Ba0.6K0.4Fe2As2 crystals, with and without columnar defects produced by 1.4 GeV 208Pb irradiation. The low temperature behavior of unirradiated samples was consistent with a fully gapped superconducting state with a minimum energy gap delta_min/(k_B T_C) = 1. Similar gap values were observed for irradiation levels corresponding to mean column-column separations of 32 nm and 22 nm. At very high irradiation levels (column-column separation of 10 nm) a T^2 power law was observed below Tc/3, most likely due to elevated scattering. Neither the location nor the sharpness of the superconducting transition was affected by irradiation. The data provides evidence for an s+/- pairing state.
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We report on the transport, magnetization, and scanning tunneling spectroscopy measurements on c-axis oriented thin films of MgB2 irradiated with high energy heavy ions of uranium and gold. We find a slight shift in the irreversibility and upper critical field lines to higher temperatures after irradiation. In addition, we observe an increase in the critical current at high temperatures near Tc2 and only a small change at low temperatures. Furthermore, we find no evidence for the existence of anisotropic pinning induced by heavy ion irradiation in this material. Tunneling spectra in an irradiated sample show a double gap structure with a flat background and very low zero-bias conductance, behaving in much the same way as the pristine unirradiated sample.
160 MeV Neon ion irradiation has been carried out on MgB2 polycrystalline pellets at various doses. There has not been any significant change in Tc except at the highest dose of 1x10^15 ions/cm^2. Increase in resistivity has been noticed. Resistivity data has been fitted with Bloch-Gruneisen function and the values of Debye temperature, residual resistivity and temperature coefficient of resistivity have been extracted for irradiated as well as unirradiated samples. The increase in the resistivity of irradiated samples has been explained in the light of damage in the 3D pi bonding network of B.
A single crystal of isovalently substituted Ba(Fe$_{1-x}$Ru$_{x}$)$_2$As$_2$ ($x=0.24$) was sequentially irradiated with 2.5 MeV electrons up to a maximum dose of $2.1 times 10^{19}$ electrons/cm^2. The electrical resistivity was measured textit{in - situ} at $T=$22 K during the irradiation and textit{ex - situ} as a function of temperature between subsequent irradiation runs. Upon irradiation, the superconducting transition temperature, $T_c$, decreases and the residual resistivity, $rho_0$, increases. We find that electron irradiation leads to the fastest suppression of $T_c$ 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 $T_c$ vs. $rho_0$ is fully compatible with $s_pm$ pairing, in contrast to earlier claims that this model leads to a too rapid a suppression of $T_c$ with scattering.
We investigate the vortex dynamics in two typical hole doped iron based superconductors CaKFe$_4$As$_4$ (CaK1144) and Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ (BaK122) with similar superconducting transition temperatures. It is found that the magnetization hysteresis loop exhibits a clear second peak effect in BaK122 in wide temperature region while it is absent in CaK1144. However, a second peak effect of critical current density versus temperature is observed in CaK1144, which is however absent in BaK122. The different behaviors of second peak effect in BaK122 and CaK1144 may suggest distinct origins of vortex pinning in different systems. Magnetization and its relaxation have also been measured by using dynamical and conventional relaxation methods for both systems. Analysis and comparison of the two distinct systems show that the vortex pinning is stronger and the critical current density is higher in BaK122 system. It is found that the Maleys method can be used and thus the activation energy can be determined in BaK122 by using the time dependent magnetization in wide temperature region, but this is not applicable in CaK1144 systems. Finally we present the different regimes with distinct vortex dynamics in the field-temperature diagram for the two systems.
The influence of irradiation by electrons with energies of $0.5-2.5$,MeV at temperatures of about $10$,K on the basal-plane resistivity of the YBa$_2$Cu$_3$O$_{7-delta}$ single crystals is investigated in the range from $T_c$ to $300$,K. The resistivity temperature dependence is determined by defects arising due to the irradiation. These defects directly affect the superconducting transition, decreasing $T_c$ and increasing the transition width without significant distortions of its shape. The resulting defects also lead to an increase in the Debye temperature due to a reduction of the anisotropy, and a noticeable increase in the scattering by phonons in the sample. The excess conductivity does not change with the irradiation used.
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