"Probing Topology and Correlation by Milli-Kelvin Microwave Microscopy"
Abstract: Near-field microwave microscopy has been an actively evolving research field in the past few decades. For the study of quantum materials, the technique is usually configured in cryogenic environments such that the thermal energy is comparable to or smaller than the scales of intrinsic quantum mechanical energy in the system. In this work, we implement a dilution-refrigerator-based scanning microwave impedance microscope (MIM) with a base temperature of 100 mK. The vibration noise of our apparatus with tuning-fork feedback control and close-cycled helium recovery is as low as 1 nm. Using this setup, we have demonstrated the imaging of various quantum materials with flat energy bands. For gated monolayer graphene, the MIM can map out the evolution of edge and bulk states around multiple integer filling factors. For H-stack twisted transition-metal dichalcogenides, the MIM can reveal the presence of correlated states at integer fillings of the moire superlattice. Our study establishes an experimental platform for investigating nanoscale quantum phenomena at ultralow temperatures.
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