Anomalous Modulation of a Zero-Bias Peak in a Hybrid Nanowire-Superconductor Device

We report on transport measurements of an InAs nanowire coupled to niobium nitride leads at high magnetic fields. We observe a zero-bias anomaly (ZBA) in the differential conductance of the nanowire for certain ranges of magnetic field and chemical potential. The ZBA can oscillate in width with either the magnetic field or chemical potential; it can even split and re-form. We discuss how our results relate to recent predictions of hybridizing Majorana fermions in semiconducting nanowires, while considering more mundane explanations.

Figure 1

(a) SEM image of NbN leads on InAs nanowire (NW). The white feature at the edges of the NbN leads is PMMA residue from the ion milling. (b) Transport at $B=0$ for $V_{\mathrm{BG}}=10.1$ V (black), 10.9 V (red, light grey ), and 11.75 V (blue, dark grey). (c) Stability diagram at $B=0$ for region of interest.

Figure 2

(a), (b) Conductance traces vs the magnetic field for two different densities. (c) Individual traces for $V_{\mathrm{BG}}=10.1\mathrm{V}$, each trace differing by 0.1 T. Adjacent curves are offset for clarity.

Figure 3

(a), (b) Conductance traces at $V_{\mathrm{BG}}=10.1\mathrm{V}$ for various $B$ values. In (b), the traces differ by $\Delta B=0.05\mathrm{T}$. Adjacent curves are offset for clarity.

Figure 4

Stability diagram at (a) $B=2.3\mathrm{T}$ and (b) $B=3.2\mathrm{T}$. In (a), dashed white lines show the location of resonant levels. In (b), dashed white lines delineate individual periods of ZBA oscillations. (c) Individual traces for $B=3.2\mathrm{T}$ in steps of $\Delta V_{\mathrm{BG}}=0.025$, with adjacent curves offset for clarity.

Figure 5

(a) ZBA temperature dependence at $B=2.75\mathrm{T}$ and $V_{\mathrm{BG}}=10.35\mathrm{V}$. (b) Peak height (black) and FWHM (red) vs $T$, after subtracting off background. Black dashed line is parabolic fit based on Ref. 37 with $T_K=970\mathrm{mK}$.