Imaging twisted MoTe₂ with scanning tunneling microscopy: Part 1

Twisted bilayer molybdenum ditelluride (tMoTe₂) has recently been found to host a variety of strongly correlated and topological states of matter, most notably the fractional quantum anomalous Hall effect arising at partial fillings of the moiré flat band. These states have been characterized using a combination of optical spectroscopy and electrical transport measurements, which necessitate averaging over micrometer-scale regions of samples. Critically, the microscopic mechanisms underlying these novel phases have yet to be directly explored. Although scanning tunneling microscopy and spectroscopy (STM/S) can serve as powerful tools for atomic-scale studies of tMoTe₂, fabricating STM/S-compatible samples presents substantial challenges owing to the high environmental sensitivity of MoTe₂ and difficulties in establishing ohmic contacts at cryogenic temperatures. Here, we summarize our efforts towards creating ultra-clean and gate-tunable tMoTe₂ samples for STM/S characterization. To prevent degradation of the exfoliated MoTe₂ crystals, we fabricate our samples in an argon-filled glove box and use a custom-built transfer suitcase to move the samples directly into the high-vacuum load lock of the STM. Using this technique, we study generations of device designs which steadily iterate towards functional electrical contacts at cryogenic temperatures. We will overview the quality of devices in each generation, leading into a discussion of the details of the atomic-scale electronic properties of tMoTe₂ in the second part of this presentation.