Implementing microwave impedance microscopy in a dilution refrigerator.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Phenomena

Background:

• Quantum anomalous Hall (QAH) states are exotic topological states of matter.
• Investigating QAH states requires advanced microscopy techniques capable of operating at extremely low temperatures.

Purpose of the Study:

• To implement a novel scanning microwave impedance microscope (SMM) operating at millikelvin temperatures.
• To demonstrate the capability of this SMM for imaging nanoscale quantum phenomena in topological materials.

Main Methods:

• Development of a dilution refrigerator-based SMM with a base temperature of ~100 mK.
• Utilized tuning-fork feedback control to achieve vibration noise as low as 1 nm.
• Grown magnetic topological insulator thin films (Cr, V doped (Bi, Sb)2Te3 on mica).

Main Results:

• Successfully imaged quantum anomalous Hall states in magnetic topological insulators.
• Visualized conductive edge modes and topological phase transitions in Cr- and V-doped (Bi, Sb)2Te3 thin films.
• Observed field-dependent behavior related to coercive fields of the magnetic dopants.

Conclusions:

• Established an experimental platform for ultralow temperature nanoscale quantum investigations.
• Demonstrated the SMM's effectiveness in visualizing complex quantum states in topological materials.
• Opened new avenues for exploring quantum phenomena at the nanoscale.