Extended Data Fig. 6: Measurement of the third harmonic of the current. | Nature

Extended Data Fig. 6: Measurement of the third harmonic of the current.

From: Evidence of topological superconductivity in planar Josephson junctions

Extended Data Fig. 6

a, G as a function of Vsd and Φ at B|| = 850 mT measured with an excitation amplitude Vac = 3 µV in device 1. b, Numerical second derivative of the conductance \(G^{\prime\prime} \left({V}_{{\rm{sd}}}\right){\left.=\left({\partial }^{2}G/\partial {V}^{2}\right)\right|}_{{V}_{{\rm{sd}}}}\) as a function of Vsd and Φ calculated from the data shown in a. c, Third harmonic of the current \({I}_{3\omega }\) versus Vsd and Φ measured by the lock-in amplifier using an excitation Vac = 15 µV, as explained in the Methods. To increase the signal-to-noise ratio, the amplitude of the excitation has been chosen to be greater than the temperature-limited full-width at half-maximum of a Lorentzian feature, that is, Vac ≈ 3.5 kBT, where \({k}_{{\rm{B}}}\) is the Boltzmann constant and T ≈ 40 mK is the electron temperature in our devices. Most of the features present in b are reproduced in c. d, e, Line cuts of G as a function of Vsd taken at \(\phi \) = 0, π as indicated by the ticks in a. f, \({I}_{3\omega }\left({V}_{{\rm{sd}}}=0\right)\) as a function of Φ: a positive value of \({I}_{3\omega }\left({V}_{{\rm{sd}}}=0\right)\) indicates a ZBP in G. See Methods for further details.

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