Anomalous Magnetothermopower Oscillations in InAs/GaSb Quantum Wells Near the Topological Phase Boundary: Extracting Edge State Contribution Through Corbino Disk Geometry at Millikelvin Temperatures

Abstract

InAs/GaSb quantum wells provide an electrically tunable platform for exploring topological thermoelectric phenomena. We investigate magnetothermopower (MTP) oscillations near the topological phase boundary using paired Corbino and Hall-bar devices microfabricated from the same wafer and measured between 20–500 mK in magnetic fields up to 14 T. The Corbino geometry, which suppresses circumferential edge conduction, serves as a bulk-only reference, while the Hall bar captures the combined edge–bulk response. Thermopower S(B,T) is recorded under a controlled millikelvin thermal gradient and analyzed via background subtraction, FFT in 1/B, and Lifshitz–Kosevich/Dingle fits. Corbino traces display bulk-like oscillations with consistent effective mass and quantum lifetime across gate bias, confirming partially coherent bulk states. Hall-bar data exhibit enhanced amplitude, a reproducible phase advance relative to the Corbino baseline, and a weak low-frequency spectral shoulder that peaks near the gate-defined hybridization gap. A geometry-assisted mixing analysis yields a sizable edge thermopower component with slower thermal damping, characterized by a finite coherence scale and an edge thermal conductance approaching the quantum limit at 100 mK. A small linear-in-field tilt in the Hall-bar baseline near the transition is captured by a Berry-curvature correction and correlates with electron–hole compensation. These results establish MTP as a sensitive probe of edge-mediated heat transport in InAs/GaSb and provide quantitative design rules—gap tuning, perimeter engineering, and controlled compensation—for cryogenic thermoelectric and spin-caloritronic devices.