Properties of FeSe nanobridges prepared by using a focused ion beam

Abstract

We have fabricated FeSe nanobridges by using a focused ion beam (FIB) etching technique and studied their transport properties. FeSe films were prepatterned into microbridges by using a standard photolithography and argon-ion-milling technique and was subsequently patterned into nanobridges by using a focused Ga+ beam with a beam current of 9 pA to minimize damage to the film. The nominal width and length of the bridges were 300 nm and 100 nm, respectively, and the film thickness was about 1,000 nm. Our film was deposited on an Al2O3(0001) substrate by using a pulsed laser deposition technique and had a (101)-oriented tetragonal phase according to its X-ray diffraction spectrum. We have studied the current-voltage (I-V) characteristics, the temperature-dependent critical current and the normal state resistance. The as-made film exhibited an onset transition temperature (T (c)) of 11.0 K and zero resistivity at 6.7 K. Argon-ion milling decreased T (c), T (c,onset) = 10.0 K, and T (c0) = 6.0 K, but subsequent FIB nanobridge patterning did not affect T (c). The measured transport properties of the nanobridges showed a flux-flow behavior with thermal fluctuations with negligible pinning effect. The results are compared with those of the MgB2 counterpart with a coherence length of similar size. The details of the fabrication procedure and the measured properties are discussed.