Proximity effect in PbTe-Pb hybrid nanowire Josephson junctions

Semiconductor-superconductor hybrid nanowires are a leading material platform for the realization of Majorana zero modes. The semiconductors in previous studies are dominantly InAs or InSb. In this paper, we show the induced superconductivity in PbTe nanowires epitaxially coupled to a superconductor Pb. The Josephson junction devices based on this hybrid reveal a gate-tunable supercurrent in the open regime and a hard superconducting gap in the tunneling regime. By demonstrating the superconducting proximity effect, our result can enable Majorana searches and other applications, such as gate-tunable qubits in a new material platform.

Figure 1

(a) SEM of a PbTe-Pb nanowire. Scale bar, 1 $\mu \mathrm{m}$. (b) The JJ schematic, cut at the red dashed line in (a). Layer thickness on the right. (c) SEM of device $A$. Scale bar, 1 $\mu \mathrm{m}$. Contacts and gate, Ti/Au (10/65 nm). (d) Device schematic.

Figure 2

Supercurrent in the open regime of device $A$. (a) $I\text{−}V$ characteristic as a function of $V_{\mathrm{G}}$. $B$ = 0 T. (b) Line cuts from (a). (c) $I_{\mathrm{excess}}$ and $R_{\mathrm{n}}$ estimations of an example $I\text{−}V$ trace. (d) Estimated PbTe-Pb interface transparency. Red and blue dots are based on the $I_{\mathrm{excess}}$ and $R_{\mathrm{n}}$ extracted from the positive and negative bias branches, respectively. (e) $R$ versus $I$ and $B$. $R=dV/dI$. $B$ is parallel to the nanowire. (f) Line cuts from (e). (g) $R$ versus $I$ and $B$. $B$ is perpendicular to the substrate. (h) Line cuts from (g). (i) $T$ dependence.

Figure 3

Superconducting gap in the tunneling regime of device $A$. (a) $dI/dV$ versus $V$ for more negative $V_{\mathrm{G}}$. $B$ = 0 T. (b) A line cut in the tunneling regime, plotted in linear (upper) and logarithmic (lower) scales. (c) $B$ (parallel to the nanowire) dependence of the gap. (d) Line cuts from (c). (e) $B$ is perpendicular to the substrate. (f) Line cuts from (e). (g) $T$ dependence of the gap.

Figure 4

STEM analysis of device $B$. (a) The high-angle annular dark field (HAADF) image of the nanowire cross section with crystal directions labeled. (b) Atomically resolved image near the Pb-CdTe (capping) interface, see the blue box in (a). (c) Image of the PbTe-CdTe interface, see the green box in (a). (d) Image of the PbTe-Pb interface, see the violet box in (a). (e)–(h), energy-dispersive x-ray spectroscopy (EDX) maps of Pb, Te, Cd, and Si, respectively. Scale bar, 50 nm.