Spin-orbit interaction in InSb nanowires

Abstract

We use magnetoconductance measurements in dual-gated InSb nanowire devices, together with a theoretical analysis of weak antilocalization, to accurately extract spin-orbit strength. In particular, we show that magnetoconductance in our three-dimensional wires is very different compared to wires in two-dimensional electron gases. We obtain a large Rashba spin-orbit strength of 0.5-1 eVÅ corresponding to a spin-orbit energy of 0.25-1 meV. These values underline the potential of InSb nanowires in the study of Majorana fermions in hybrid semiconductor-superconductor devices. Hybrid semiconductor nanowire-superconductor devices are a promising platform for the study of topological superconductivity [1]. Such devices can host Majorana fermions [2,3], bound states with non-Abelian exchange statistics. The realization of a stable topological state requires an energy gap that exceeds the temperature at which experiments are performed (∼50 mK). The strength of the spin-orbit interaction (SOI) is the main parameter that determines the size of this topological gap [4] and thus the potential of these devices for the study of Majorana fermions. The identification of nanowire devices with a strong SOI is therefore essential. This entails both performing measurements on a suitable material and device geometry as well as establishing theory to extract the SOI strength.InSb nanowires are a natural candidate to create devices with a strong SOI, since bulk InSb has a strong SOI [5,6]. Nanowires have been used in several experiments that showed the first signatures of Majorana fermions [7][8][9][10]. Nanowires are either fabricated by etching out wires in planar heterostructures or are grown bottom up. The strong confinement in the growth direction makes etched wires two dimensional (2D) even at high density. SOI has been studied in 2D InSb wires [11] and in planar InSb heterostructures [12], from which a SOI due to structural inversion asymmetry [13], a Rashba SOI α R of 0.03 eVÅ has been obtained [12]. Bottom-up grown nanowires are three dimensional (3D) when the Fermi wavelength is smaller than the wire diameter. In InSb wires of this type, SOI has been studied by performing spectroscopy on quantum dots [14,15] [19,20]. Our approach is to use a high-k dielectric in combination with a top gate that covers the InSb nanowire. The standard method to extract SOI strength in extended regions is through low-field magnetoconductance (MC) measurements [21,22]. Quantum interference (see Fig. 1) in the presence of a strong SOI results in an increased conductance, called weak antilocalization (WAL) [23], that reduces to its classical value when a magnetic field is applied [24]. From fits of MC data to theory a spin relaxation length is extracted. If spin relaxation results from inversion asymmetry, a spin precession length and SOI strength can be defined. To extract SOI strength in nanowires the theory should contain (1) the length over which the electron dephases in the presence of a magnetic field, the magnetic dephasing length [25], and (...

Magnetoconductance correction in zinc-blende semiconductor nanowires with spin-orbit coupling

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Observation of coherent electron transport in self-catalysed InAs and InAs1–xSbx nanowires grown on silicon

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