Fabrication of BaKFeAs intergrain nanobridges by using a focused ion beam

Abstract

We have studied the fabrication and the transport properties of Ba_0.6K_0.4Fe₂As₂ intergrain nanobridges patterned by using a focused ion beam (FIB). Prior to FIB etching, 8-µm-wide bridges were prepatterned from Ba_0.6K_0.4Fe₂As₂ 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 (I _c ), 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 I _c ∼ (1 − T/T _c )1.0.