FeTe0.55Se0.45 van der Waals tunneling devices

We report on fabrication of devices integrating FeTe0.55Se0.45 with other van der Waals materials, measuring transport properties as well as tunneling spectra at variable magnetic fields and temperatures down to 35 mK. Transport measurements are reliable and repeatable, revealing temperature and magnetic field dependence in agreement with prior results, confirming that fabrication processing does not alter bulk properties. However, cross-sectional scanning transmission microscopy reveals oxidation of the surface, which may explain a lower yield of tunneling device fabrication. We nonetheless observe hard-gap planar tunneling into FeTe0.55Se0.45 through a MoS2 barrier. Notably, a minimal hard gap of 0.5 meV persists up to a magnetic field of 9 T in the ab plane and 3 T out of plane. This may be the result of very small junction dimensions or a quantum-limit minimal energy spacing between vortex bound states. We also observe defect-assisted tunneling, exhibiting bias-symmetric resonant states, which may arise due to resonant Andreev processes.