Harmonic detection of the Majorana fermion in narrow bandgap InAsSb

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Non-Technical Abstract:This project will develop an alternative measurement scheme using harmonic generation in a novel hybrid capacitor device aimed to circumvent the fundamental limitations of conventional methods to settle the (still open) question: Has the solid-state "Majorana fermion¨ been seen? This novel state of matter, theoretically predicted to have unusual behaviors, is induced by superconductivity and electron interactions in certain semiconductor structures. Its discovery and manipulation in appropriately-design circuits could lead to the creation of a new kind of quantum computer which is essentially immune to decoherence.Technical Abstract:This project will develop a measurement technique utilizing harmonic generation in a novel hybrid capacitor device to measure global density of states of a low-dimensional electronic material without perturbative ohmic contact. It is motivated by a need to definitively identify zero-bias tunnel-transport anomalies in spin-orbit-coupled one-dimensional superconductors as possible signatures of a predicted topological electronic excitation localized to wire endpoints called the "Majorana fermion¨.Briefly, the electrostatic potential of an intermediate material floats between the capacitor electrodes, and can exchange electrons with one (grounded) electrode via tunneling. Capacitive coupling to the top electrode at voltage V(t) induces a voltage drop between the floating material and the bottom grounded electrode, driving elastic tunneling which is sensitive to the global density of states. If the capacitive impedance at the driving frequency is comparable to the characteristic (voltage-dependent) tunnel resistance, the nonlinear conductance spectrum components will be encoded into the higher harmonic response of the device.Importantly, the research team intends to fabricate the nanowires using high-quality InAsSb (from collaborators at nearby Adelphi Army Research Laboratory), which has a lower bandgap than either of the binary constituents InAs or InSb. The team will work toward confirming that it also has a lower effective mass, higher g-factor, and larger spin-orbit interaction (as predicted by k-dot-p theory. All of these parameters will substantially optimize the Majorana formation and its topological protection to enhance the possibility of detection using our harmonic generation measurement.