Superconductivity of nanostructured Ga–Sn alloy

The paper presents studies of superconductivity of the eutectic gallium-tin alloy embedded into pores of the opal matrix. Low-temperature measurements of the dc and ac magnetizations were carried out within a wide range of magnetic fields. Three superconducting transitions were observed. The constructed $H$–$T$ phase diagram demonstrated the positive curvature of the critical lines at small magnetic fields. It was explained using a model, which takes into account the proximity effect. For two transitions, it was shown that the motion of superconducting vortices was thermally activated. Arrhenius plots were constructed and activation energies for different bias fields were calculated. The sharp decrease in the activation barriers was observed at the same range of magnetic fields as the change in the critical lines curvature, which was ascribed to transformations in the superconducting vortex system.