Phase controlled multi-terminal Josephson junction in ternary hybrid nanowire

TL;DR

This work addresses the realization of scalable multiterminal Josephson junctions in a ternary InAsSb-Al nanowire network. By growing As-assisted InAsSb nanocrosses via MBE and performing detailed atomic-scale characterization, the authors establish a four-terminal superconducting platform with coherent phase relationships among all terminals, tunable by external magnetic flux and gate voltage within a four-terminal RSJ framework. They demonstrate measurable supercurrents for all terminal pairs, a central four-terminal superconducting region, and gate-controlled conductance enabling access to near single-channel operation. The resulting platform offers a versatile route to complex superconducting circuits and potential quasiparticle braiding in solid-state devices.

Abstract

This work presents multiterminal Josephson junctions in hybrid semiconductor-superconductor InAsSb-Al nanocrosses. Hybrid nanocrosses are grown using molecular beam epitaxy and are formed through As-assisted merging of oppositely directed InAsSb nanowires. We explain this complex ternary merging mechanism using a temperature-dependent phase diagram and investigate the detailed crystal structure with atomic-resolution imaging. The hybrid nanoscrosses enabled the fabrication of multiterminal Josephson junction devices, which were characterized at low temperatures. The supercurrent through each terminal combination was measured as a function of the density in the junction and the relative phase of the terminals, which was controlled by an external magnetic field.

Figures (4)

• Figure 1: Formation of the ternary network.a, Scanning electron microscopy of InAsSb-Al nanocrosses grown from the V-grove trenches. To the right, Electron Energy Loss Spectroscopy elemental maps show the spatial distribution of In, As, Sb and Al. b, The Phase diagram of the possible crystal structure of ternary NW as a function of Sb composition and growth temperature. With growth temperature around 450$^{\circ}$ C and intended Sb percentage of 60-70% we expected to achieve ZB crystal. c, Schematic of the NW growth in different stages of As and Sb diffusion length. All the fluxes are open and As assists in axial growth whereas later stage Sb contributes radial broadening. d, Sb driven radial growth helps NWs to get closer and possibly connect in through side-wall. e, Post growth radial broadening with additional As flux to merge the NWs properly. f, Schematic of two As-assisted integration mechanisms (referred as (1) and (2)) simultaneously occur to merge the NW. Scale bars are: (a) 1 µ m.
• Figure 2: Structural analysis of InAsSb nanocrosses.a, Low-magnification HAADF-STEM micrograph of the four-terminal InAsSb junction. ‘Green’ and ‘Red’ arrows in the four legs (labelled L1-4) indicate each NW growth direction before and after merging. The power spectrum of micrographs acquired at each terminal are displayed to show the crystal plane directions of every leg. b, FFT from the central area of the junction showing coexistence of both crystal orientations, which join together forming twin boundaries. c, The atomic arrangement across the twin in the central area with the corresponding crystal directions labelled. d, Atomic models showing the crystal orientation in the different terminals of the network.
• Figure 3: Supercurrents in an InAsSb-Al multi-terminal Josephson device.a, False colored SEM of a typical device with a schematic of the employed measurement circuit. Superconducting contacts are in orange, and exposed semiconducting InAsSb in green. b, Schematic of RSJ-based circuit used to simulate the overall characteristics of the devices. c, Simulated differential resistance, $R_\mathrm{AB}$, from terminal $A$ to $B$ as a function of the applied currents. d-f, Measured differential resistances from terminal $A$ to $B$ ($R_\mathrm{AB}$), from $A$ to $C$ ($R_\mathrm{AC}$), and from $B$ to $C$ ($R_\mathrm{BC}$), respectively. g-h, Differential resistance, $R_\mathrm{AB}$ measured at two different phase differences $\phi =0$ and $\phi = \pi$, respectively. i-h, The corresponding phase dependence measured along the three paths $\alpha, \beta, \gamma$, as indicated in (d-f). The measurements were performed at $T=20 \, \mathrm{mK}$ and $V_{G}=40$.
• Figure 4: Gate- and phase dependence of Multi-terminal Josephson device.a-b, Differential resistance, $R_\mathrm{AB}$ at back-gate potentials, $V_\mathrm{G}$, of $0\,\mathrm V$ and $-40 \, \mathrm V$, respectively. c-d, the gate dependence of the normal state resistances and critical currents between the three pairs of terminals.