Fermi-arc supercurrent oscillations in Dirac semimetal Josephson junctions

Abstract

One prominent hallmark of topological semimetals is the existence of unusual topological surface states known as Fermi arcs. Nevertheless, the Fermi-arc superconductivity remains elusive. Here, we report the critical current oscillations from surface Fermi arcs in Nb-Dirac semimetal Cd₃As₂-Nb Josephson junctions. The supercurrent from bulk states are suppressed under an in-plane magnetic field ~0.1 T, while the supercurrent from the topological surface states survives up to 0.5 T. Contrary to the minimum normal-state conductance, the Fermi-arc carried supercurrent shows a maximum critical value near the Dirac point, which is consistent with the fact that the Fermi arcs have maximum density of state at the Dirac point. Moreover, the critical current exhibits periodic oscillations with a parallel magnetic field, which is well understood by considering the in-plane orbital effect from the surface states. Our results suggest the Dirac semimetal combined with superconductivity should be promising for topological quantum devices.

Fig. 1. Josephson effect in a Nb-Cd₃As₂-Nb junction.

a Optical image of the Nb-Cd₃As₂ nanoplate-Nb Josephson junctions. Scale bar, 2 μm. b The color-scale differential resistance dV/dI as a function of gate voltage V_g and d.c bias current I_dc. c The dV/dI versus source-drain voltage V_dc across the junction, showing the multiple Andreev reflections.

Fig. 2. The supercurrent oscillations under parallel magnetic field at V_g = 0 V.

a The dV/dI as a function of magnetic field B and I_dc. The I_dc is swept from negative to positive. The applied excitation current I_ac = 0.5 nA. Inset: Schematic of the magnetic field direction on the junction. b The enlarged dV/dI map of the gray dotted box in a. Periodic supercurrent oscillations with multiple nodes are observed. c The magnetic field dependence of I_c with a semilog coordinate. The Gaussian fitting (blue curve) well models the decay trend of I_c at low B, and an exponential decay (red line) fits better the data for B > 0.1 T. d The extracted ΔI_c by subtracting a smooth background as a function of B. A period of ΔB = 0.05 T is obtained from the oscillations.

Fig. 3. Gate dependence of supercurrent oscillations.

a, b Color-scale plot of dV/dI as a function of B and I_dc at different V_g as denoted. c The extracted ΔI_c versus B at different V_g. The curves have been shifted for clarity. d The comparison between critical current I_c and normal-state conductance G_N as a function of V_g, measured at B = 0.1 T. e I_c(V_g) evolutions under different magnetic fields. The I_c(0T) divided by 13 is shown in the figure. The I_c(0.18T) and I_c(0.23T) are extracted from the I_c(B) peaks of the first and second oscillation lobes in c, respectively. f The Fermi arcs for the Fermi level (up panel) close to and (bottom panel) away from Dirac point. The bulk Dirac points are projected on (112) crystal plane of the Cd₃As₂ nanoplate.

Fig. 4. The evolution of differential resistance with magnetic field B and V_g.

a The dV/dI as a function of B and V_g with I_ac = 1 nA and without applying I_dc. The vertical dashed lines are eyes guided. b The cut lines of dV/dI as a function of B extracted from a at V_g = 30, 10, 5, 1, and −10 V, respectively. The curves have been shifted for clarity. The dV/dI peaks emerge periodically with a period of ΔB = 0.055 T.

Fig. 5. Modeling Josephson interference in regime of in-plane field orbital effect.

a Within two superconducting (SC) leads, pairing electrons traverse from position x₁ of SC1 to position x₂ of SC2, accumulating phase ϕ₂(x₂) − ϕ₁(x₁). b The fit of I_c for B > 70 mT using the model of surface in-plane field orbital effect. The experimental data are from the I_c(B) at V_g = −10 V.