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| Home > Publications database > Optimization of Magnetic Topological Insulators for Superconducting Applications |
| Poster (After Call) | FZJ-2026-01389 |
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2025
Abstract: Magnetic topological insulators are predicted to be a promising platform for scalable topological quantum computation [1,2]. In the one-dimensional limit the chiral edge modes on opposite sides of a quantum anomalous Hall system hybridize to form a single helical conducting channel. Proximitizing this channel with an s-wave superconductor leads to the appearance of Majorana zero modes. This work makes an effort to optimize the magnetic topological insulator, composed out of Cr-doped (BixSb1-x)2Te3, for these superconducting applications. One approach is to modify the magnetic properties of the films via controlling the parameters during molecular beam epitaxy growth. Van der Pauw measurements are performed on magnetic topological insulator thin films with different material compositions. This approach allows for a fast optimization of the material and a systematic study of the interplay between growth parameters and magneto-transport signatures. We show how the material can be made charge neutral either by varying the substrate temperature during growth or, more directly, by varying the chromium concentration of the thin films in small amounts to compensate for the residual charges in the underlying (BixSb1-x)2Te3. Furthermore, by lowering the chromium concentration to values much smaller than those typically used for quantum anomalous Hall systems [3] the material can be tuned into a parameter space that, according to theoretical proposals, is beneficial for maximizing the induced superconducting gap [4]. The magnetotransport measurements on these weakly-doped thin films indicate that even at very low chromium concentrations of around 2%, the anomalous Hall resistance can reach up to 60% of the quantized value at a temperature of 1.2 K. This suggests that it may be possible to enter the quantum anomalous Hall regime even with low intrinsic magnetizations. In addition to the material optimization, novel ways to fabricate nanometer-sized magnetic topological insulator/superconductor hybrid devices based on shadow walls and stencil masks are being explored. These techniques avoid lithography and etching steps that are otherwise known to be harmful for the material. Based on this, Hall bars from Cr-doped (BixSb1-x)2Te3 are fabricated in the micrometer and nanometer size ranges and their electric and magnetic properties are investigated. No significant difference was found between the micrometer- and nanometer-sized Hall bars, indicating that the fabrication technique does not change the material composition. This hypothesis is supported by transmission electron microscopy and energy-dispersive X-ray spectroscopy measurements.[1] C.-Z. Chen, et al., Physical Review B 97, 104504 (2018).[2] X.-L. Qi, et al., Physical Review B 82, 184516 (2010).[3] C.-Z. Chang, et al., Advanced materials 25, 1065 (2013).[4] D. Burke, et al., Phys. Rev. B 109, 045138 (2024).
Keyword(s): Information and Communication (1st) ; Condensed Matter Physics (2nd)
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