Superconductivity in the system $\rm Mo_xC_yGa_zO_δ$ prepared by focused ion beam induced deposition

Abstract: We have prepared the new amorphous superconductor $\rm Mo_xC_yGa_zO_{\delta}$ with a maximum critical temperature $T_c$ of 3.8\,K by the direct-write nano-patterning technique of focused (gallium) ion beam induced deposition (FIBID) using $\rm Mo(CO)_6$ as precursor gas. From a detailed analysis of the temperature-dependent resistivity and the upper critical field we found clear evidence for proximity of the samples to a disorder-induced metal-insulator transition. We observed a strong dependence of $T_c$ on the deposition parameters and identified clear correlations between $T_c$, the localization tendency visible in the resistance data and the sample composition. By an in-situ feedback-controlled optimization process in the FIB-induced growth we were able to identify the beam parameters which lead to samples with the largest $T_c$-value and sharpest transition into the superconducting state.