DNA-assembled superconducting 3D nanoscale architectures

Abstract

Studies of nanoscale superconducting structures have revealed various physical phenomena and led to the development of a wide range of applications. Most of these studies concentrated on one- and two-dimensional structures due to the lack of approaches for creation of fully engineered three-dimensional (3D) nanostructures. Here, we present a 'bottom-up' method to create 3D superconducting nanostructures with prescribed multiscale organization using DNA-based self-assembly methods. We assemble 3D DNA superlattices from octahedral DNA frames with incorporated nanoparticles, through connecting frames at their vertices, which result in cubic superlattices with a 48 nm unit cell. The superconductive superlattice is formed by converting a DNA superlattice first into highly-structured 3D silica scaffold, to turn it from a soft and liquid-environment dependent macromolecular construction into a solid structure, following by its coating with superconducting niobium (Nb). Through low-temperature electrical characterization we demonstrate that this process creates 3D arrays of Josephson junctions. This approach may be utilized in development of a variety of applications such as 3D Superconducting Quantum interference Devices (SQUIDs) for measurement of the magnetic field vector, highly sensitive Superconducting Quantum Interference Filters (SQIFs), and parametric amplifiers for quantum information systems.

Fig. 1. Schematics of 3D superlattice assembly from octahedra DNA frames and gold nanoparticle, and its conversion into silica and superconductive structure.

a DNA origami octahedral frames. b Integration of DNA frames with gold 10 nm nanoparticles and assembly of frames into superlattice with cubic unit cell. (AuNP used here for structural characterization and are not shown in other schematics). c Stepwise conversion process from DNA superlattices to SiO₂ and to Nb-coated structures. d Schematic of the formed simple cubic arrangement of octahedra frames. A tetragonal arrangement AuNP’s is determined by SAXS: data (orange), model (blue), indexed diffraction peaks, (001), (100), (101), (111), (002), (200) etc., are shown with vertical black lines. SEM micrographs of e large scale and f close up images of fabricated silica superlattices. g Schematic of low-temperature electrical measurement setup for Nb superlattice using four-point probe.

Fig. 2. Electron microscopy characterization and element analysis of Nb-coated superlattice.

a SEM image of the top layer of one of the Nb-coated superlattice flakes. b SEM of magnified region with inset figure denoting the array arrangement of S-s-S Josephson junctions with large grains grown on the octahedron (gray diamond) with small connections formed at vertices (yellow). c HAADF image of Nb-Superlattice representative of underlying layers of surface shown in b, AuNP appear white while the silica superlattice appears gray on a black background. d EDS map with column sums of first three layers (gold, red, and blue) of the Nb superlattice as indicated by the appearance of AuNP in red. e HAADF image of the same region with AuNP in white with the silica lattice in a lighter tone. f EDS highlighting the Nb spectrum K-edge peak at 16.58 KeV. Inset is a log scale of column 3 (blue), shown in d, at the same energy.

Fig. 3. Temperature dependence of the resistance of a Nb-coated superlattice.

The superconducting transition T_c ~ 3.8 K at zero field. Inset: Resistance versus temperature at zero field for the reference sample, a 10 nm thick Nb film; T_c ~ 5 K.

Fig. 4. Current-voltage (I–V) characteristics of a Nb-coated superlattice.

I–V characteristics for 1.9–3.7 K with ΔT = 0.2 K. Right inset: V–I characteristics (open dots) at 1.9 and 3.7 K. Solid line for the 1.9 K data is a fit to Equation (1). Solid line for the 3.7 K data is a fit to a power law, yielding V ∝ I^2.3. Left inset: Critical current derived from the I–V curves as a function of temperature. The error in each point is estimated as 2–3%. Solid orange and green lines are guide to the eye, emphasizing the different behavior at high and low temperatures.

Fig. 5. Magnetoresistance of the Nb-coated superlattice as a function of the applied magnetic field.

R normalized to R_n = 260 Ω vs. H at temperatures 3.6, 3.62, 6.64, 3.68, 3.72, and 3.76 K. The dotted line is a fit to Equation (2) for T = 3.6 K. Inset: Calculated magnetoresistance based on Equation (2) for t = T/T_c = 0.92 to 0.98.