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Figure 1.  Schematic diagram of the MgB₂ Josephson junction fabrication process before He-FIB irradiation, including thin films growth, sputtering Ag electrical bonding pads, lithography, and etching.

Figure 2.  (a) Schematic diagram of a MgB₂ Josephson junction fabricated by He-FIB. (b) Optical microscope photograph under bottom light where black line indicates irradiation trace. (c) R–T curves of junctions 1 and 2, where the inset is a close-up view. (d) V–I curves of junctions 1 and 2 at 2 K, where the inset shows the dV/dI–I curves.

Figure 3.  (a) and (c) The I–V curves and dV/dI–V curves of junctions 1 and 2 under magnetic field and RF radiation at 2 K where clear integer and half-integer Shapiro steps can be observed. The positions of steps are labeled by vertical lines and the corresponding normalized voltages n represent the orders of steps. (b) and (d) The vertically shifted dV/dI–V curves of junctions 1 and 2 under different frequencies of RF radiation. The voltages corresponding to the steps rise with the increase of frequency.

Figure 4.  (a) and (c) Selected I–V curves of junctions 1 and 2 under fixed RF radiation power and magnetic field at different temperatures. (b) and (d) Heatmaps of junctions 1 and 2’s I–dV/dI curves at different temperatures. The white areas indicate integer and half-integer Shapiro steps, which are labeled by red dashed lines.

Figure 5.  (a) and (c) The I–V curves of junction 1 under different RF radiation powers at magnetic fields of 27 Oe and 31.5 Oe. Half-integer steps only appear at the magnetic field of 27 Oe. (b) and (d) Heatmaps of I–dV/dI curves whose data is collected from (a) and (c), where red dashed lines label the evolution of step heights with radiation power and oscillations can be observed.

Figure 6.  (a) Colormap of V–dV/dI curves under radiation at different magnetic fields H, where blue areas indicate the appearance of steps. Half-integer steps are labeled by horizontal black dashed lines. (b) The critical current I_c that is modulated by magnetic field H for the positive and negative current directions. The data is also collected from junction 1.

Figure 7.  (a) Schematic diagram of a YBCO grain boundary junction which is composed of many superconducting and normal fragments and is actually a 1D junction array. (b) The irradiation mode of He-FIB, which is spot-by-spot, inducing many areas with different irradiation doses.