Use of Focused Ion Beam to Investigate Supercurrent Propagation in Topological-Insulator Single-Crystals

Focused Ion Beam (FIB) techniques enable subtractive and additive high-resolution nanopatterning processes with a wide range of applications [1, 2]. In particular, FIB milling as well as FIB-induced deposition (FIBID) processes have found application in the development of quantum technologies [3]. FIBID relies on a gas precursor that is injected into the area of interest and decomposed by FIB irradiation. Using the W(CO)₆ precursor and Ga⁺ or He⁺ FIBID processes, we have grown and investigated the properties of a large number of in-plane and out-of-plane superconducting W-C nanostructures [4], in particular Josephson junctions and nanoSQUIDs [5]. We have recently developed a new approach to extract small crystals from a larger piece, place it on a prepatterned substrate and grow electrical contacts to study its magnetotransport properties [6]. In my talk, I will show the obtained results regarding the use of topological-insulator Bi₂Se₃ crystals and W-C superconducting contacts. We have observed that it is possible to create supercurrents between the W-C contacts that travel through the (sub)surface of the Bi₂Se₃ crystals, despite the fact that the crystal becomes amorphized a few nm below the surface after the Ga⁺-FIB milling process. It is also found that the conduction channels travelling through the crystal can give rise to unconventional interference patterns in the dependence of the critical current with the applied magnetic field. The interfacial states between the amorphous and crystalline parts of the crystal could play a role, as recently claimed in the case of Bi₂Te₃[7].<br/><br/>[1] J. M. De Teresa (ed.), book on Nanofabrication, Institute of Physics, (2020), chapter 5, doi: 10.1088/978-0-7503-2608-7ch5<br/>[2] K. Höflich et al., Appl. Phys. Rev. 10 (2023) 041311<br/>[3] J. M. De Teresa, Materials in Quantum Technology 3 (2023) 013001<br/>[4] P. Orús, F. Sigloch, S. Sangiao, J.M. De Teresa, Nanomaterials 12 (2022) 1367<br/>[5] F. Sigloch, P. Orús, S. Sangiao, J.M. De Teresa, Nanoscale Advances 4 (2022) 4628<br/>[6] R. Gracia-Abad et al., submitted (2024)<br/>[7] A. Bake et al., Nature Communications 14 (2023) 1693