E. Lehmann

Observation of the crossover from two-gap to single-gap superconductivity through specific heat measurements in neutron-irradiated MgB2.

We report specific heat measurements in neutron irradiated MgB2 samples, for which the critical temperature has been suppressed down to 8.5 K, but the superconducting transition remains extremely sharp, indicative of a defect structure extremely homogeneous. Our results demonstrate that the two-gap feature is evident in the temperature range above 21 K, while the single-gap superconductivity is well established as a bulk property not associated to local disorder fluctuations when Tc is decreased down to 11 K.

Effects of neutron irradiation on polycrystalline Mg 11 B 2

We studied the influence of the disorder introduced in polycrystalline MgB2 samples by neutron irradiation. To circumvent self shielding effects due to the strong interaction between thermal neutrons and 10B we employed isotopically enriched 11B which contains 40 times less 10B than natural B. The comparison of electrical and structural properties of different series of samples irradiated in different neutron sources, also using Cd shields, allowed us to conclude that, despite the low 10B content, the main damage mechanisms are caused by thermal neutrons, whereas fast neutrons play a minor role. Irradiation leads to an improvement in both upper critical field and critical current density for an exposure level in the range 1-2x1018 cm-2. With increasing fluence the superconducting properties are depressed. An in-depth analysis of the critical field and current density behaviour has been carried out to identify what scattering and pinning mechanisms come into play. Finally the correlation between some characteristic lengths and the transition widths is analysed.

Enhanced flux pinning in neutron irradiated MgB2

We study the effect of neutron irradiation on the critical current density

Systematic study of disorder induced by neutron irradiation in MgB2 thin films

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Point-contact spectroscopy in neutron-irradiated Mg11B2

of isotopically pure polycrystalline

Direct TEM observation of nanometric-sized defects in neutron-irradiated MgB2 bulk and their effect on pinning mechanisms

\mathrm{Mg}\phantom{\rule{0.2em}{0ex}}^{11}\mathrm{B}_{2}

Magnetoresistivity as a probe of disorder in the it and σ bands of MgB2

samples. For fluences in the range

Probing the electron-phonon coupling in MgB2 through magnetoresistance measurements in neutron irradiated thin films

{10}^{17}\char21{}{10}^{18}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}

Critical field of magnesium diboride in substituted and irradiated samples

,

Magnetization decay in neutron irradiated MgB2 bulk samples

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