Measurements of cyclotron resonance of the interfacial states in strong-spin orbit coupled 2D electron gases proximitized with aluminum.*

The two dimensional electron gas (2DEG) in InAs proximitized by aluminum (Al) is a promising platform for topological qubits based on Majorana zero modes. However, there are still substantial uncertainties associated with the nature of the electronic states at the interfaces of these system. In this work we have investigated a range of In_1-xGa_xAs heterostructures with Al overlayers using high precision time-domain THz spectroscopy. In magnetic field a prominent cyclotron resonance is observed that can be associated with the response of the interfacial states. Measurements of the THz range complex Faraday rotation allow the extraction of the sign and magnitude of the effective mass, density of charge carriers, and scattering times. We compare the results of measurements with numerical calculations.