Preparation of amorphous bismuth films by quenched condensation insode of a superconducting magnet

Topological phases in crystalline materials have drawn intense research interest due to their fundamentally unique properties and potential for applications ranging from quantum computation to spintronics. Recently, scientists have extended the theoretical study of topology to a new class of materials: amorphous solids. Despite the growing interest in this new field, there remains a gaping need for new experimental tools to identify topological states in amorphous matter. Particularly challenging is the formation and study of amorphous metal films since they transform irreversibly to the crystalline state at very low temperature (∼ 25 K). In the past, cryoevaporators were built to form metal films with extreme structural disorder by condensation onto substrates cooled to He-temperature. To avoid crystallization, these cryogenic systems had to be extremely large and include multiple cooling stages, shutters and heat shields to limit the heat flow to the substrate during the evaporation process (Fig. 1(A)). Although very successful in forming amorphous films, these cryoevaporators did not allow the application of the large magnetic fields needed to adequately probe topological properties. In this thesis, we solve this problem by building a compact evaporator that allows the formation of amorphous metal films directly inside of a superconducting magnet (Fig. 1(B)). Our system uses a simple off-the-shelf platinum-chip temperature sensor as a heating source to evaporate metals onto a sapphire substrate at Hetemperature. The designed probe was used to form Bi films and measure the temperature dependence of their electrical resistance. The deposited films displayed a superconductive and crystallization transition, clearly indicating that we have successfully formed amorphous Bi. To showcase how the developed method can successfully probe amorphous metals in high fields, the film resistance was measured as a function of magnetic field up to 14 T. Reducing the cost into the one franc level and miniaturizing the size to cm3, this work democratizes the study of amorphous Bi and expedites related studies into its topological nature.