Superconducting contacts and quantum interference phenomena in monolayer semiconductor devices

In this doctoral thesis, we developed a novel method to equip a two-dimensional layer of the semiconductor molybdenum disulfide with superconducting contacts for the first time.
For future applications in electronics, researchers are studying semiconductors made of only single atomic layers. Using our method we can stack such monolayers to develop new materials with novel properties. In part, these are based on complex quantum mechanical phenomena that can be used in quantum technology. To better study these phenomena, we achieved low resistance superconducting contacts using vertical interconnect access (VIA) method.
It is imperative to protect the air sensitive materials, since impurities and defects strongly affect the transport of electric charge. In our research, we encapsulated monolayer of semiconductor using layers of insulating boron nitride. In advance, however, we embedded the vertical superconducting contacts in this protective layer. In principle, these newly developed vertical contacts to the semiconductor layers could be applied to a variety of different semiconductors.
We report quantum coherent transport in molybdenm disulfide based semiconductor-superconductor hybrid electronic device. The intrinsic properties of the semiconductor is preserved, and a high electron mobility of 2000-5000 cm2/VS is achieved in our measurements. We find a series of quantum interference effects, suggesting coherence length larger than mean free path lmfp < lφ ≈ 300 nm. In addition, Andreev bound states resonances at energies below the superconducting gap is observed. The dimensionality of the system which is inherently 2D adds a new characteristics to these Andreev bound states. Furthermore, we observed a minigap well below the superconducting gap. In addition, we measured a zero bias peak anomaly at finite magnetic field between 2-3.5 T.