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Hudson, K. L.; Srinivasan, A.; Goulko, O.; Adam, J.; Wang, Q.; Yeoh, L. A.; Klochan, O.; Farrer, I.; Ritchie, D. A.; Ludwig, A.; Wieck, A. D.; Delft, J. von and Hamilton, A. R. (2021): New signatures of the spin gap in quantum point contacts. In: Nature Communications, Vol. 12, No. 1, 5

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One dimensional semiconductor systems with strong spin-orbit interaction are both of fundamental interest and have potential applications to topological quantum computing. Applying a magnetic field can open a spin gap, a pre-requisite for Majorana zero modes. The spin gap is predicted to manifest as a field dependent dip on the first 1D conductance plateau. However, disorder and interaction effects make identifying spin gap signatures challenging. Here we study experimentally and numerically the 1D channel in a series of low disorder p-type GaAs quantum point contacts, where spin-orbit and hole-hole interactions are strong. We demonstrate an alternative signature for probing spin gaps, which is insensitive to disorder, based on the linear and non-linear response to the orientation of the applied magnetic field, and extract a spin-orbit gap Delta E approximate to 500 mu eV. This approach could enable one-dimensional hole systems to be developed as a scalable and reproducible platform for topological quantum applications. In one-dimensional systems, the combination of a strong spin-orbit interaction and an applied magnetic field can give rise to a spin-gap, however experimental identification is difficult. Here, the authors present new signatures for the spin-gap, and verify these experimentally in hole QPCs.

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