Fano Interference between Bulk and Surface States of a Dirac Semimetal ${\mathrm{Cd}}_3{\mathrm{As}}_2$ Nanowire

Dirac semimetals possess Fermi-arc surface states, which will be a set of discrete surface subbands in a nanowire due to the quantum confinement effect. Here, we report a tunable Fano effect induced by the interference between the discrete surface states and continuous bulk states of a Dirac semimetal ${\mathrm{Cd}}_3{\mathrm{As}}_2$ nanowire. The discrete surface bands lead to a zero bias peak in conductance as the Femi level is tuned to across the surface subbands. The Fano resonance results in an asymmetric line shape in the differential conductance $dI/dV$ spectrum. Furthermore, the Fano interference would introduce an additional phase into the Weyl orbits and lead to a modification of the oscillation frequency. The results are valuable for further understanding the exotic quantum transport properties of topological semimetals.

Figure 1

(a) SEM image of a typical ${\mathrm{Cd}}_3{\mathrm{As}}_2$ nanowire device. (b) The resistance versus $V_g$ measured by a four-terminal configuration. The inset shows the conductance oscillations after subtracting the background. (c) Because of quantum confinement along the nanowire circumference, a series of surface subbands develop. The red and blue lines correspond to different chirality. The purple curve indicates the DOS distribution.

Figure 2

(a) The $dI/dV$ spectra measured as a function of bias voltage $V_b$ at 2 K and at different gate voltages. The zero bias peak transforms to a zero bias dip as tuning $V_g$ from $-11.5$ to $-18.5\mathrm{V}$. (b) A similar evolution of $dI/dV$ spectrum in another $V_g$ region 14–16 V.

Figure 3

(a) The $dI/dV$ spectra as a function of $V_b$ measured at $T=2\mathrm{K}$, $V_g=14\mathrm{V}$, and under different magnetic fields. (b) The mapping of the $dI/dV$ spectra versus bias voltage and magnetic field. The red dotted lines show the linear splitting of the ZBP with magnetic field. (c) The $dI/dV$ spectra measured at different temperatures. (d) The power-law fitting of the ZBP magnitude versus temperature. The inset shows the full width at half maximum (FWHM) of the ZBP as a function of temperature. The linear fitting indicates the thermal broadening effect.

Figure 4

(a)–(c) The Fano fittings of the asymmetric line shape of the $dI/dV$ spectra. (d) The symmetric parabolic $dI/dV$ spectra near Dirac point in another sample with large diameter over 150 nm.