Fabrication of BaKFeAs intergrain nanobridges by using a focused ion beam

We have studied the fabrication and the transport properties of Ba0.6K0.4Fe2As2 intergrain nanobridges patterned by using a focused ion beam (FIB). Prior to FIB etching, 8-µm-wide bridges were prepatterned from Ba0.6K0.4Fe2As2 films by using argon ion milling with a photoresist mask. The lowest-possible beam current of 1.5 pA was used for the FIB nanobridge pattern to minimize the etching damage to the bridge. The nanobridge contained a single grain boundary, and the nominal dimensions were 200 nm in width and 100 nm in length. We have also studied current-voltage (I-V) characteristics, the temperature-dependent critical current (Ic), and the normal-state resistance (RN). The transport measurements of the nanobridge showed a strong-coupling nature with a high critical current density of 1.25 × 106 A/cm2 at 4.2 K, which is comparable to the intragrain value. The nanobridge showed the onset of a resistive transition at 37 K and zero resistance at 27 K. Measured I-V curves were dominated mainly by Josephson coupling, showing resistivelyshunted-junction (RSJ) behaviors with multiple transitions at low temperatures. The temperature dependence of the critical current was Ic ∼ (1 − T/Tc)1.0.