Encapsulation epitaxy of air-stable 2D superconductors for quantum circuits

Two-dimensional (2D) materials have garnered significant attention in the realm of quantum information science due to their unique properties, such as reduced dimensionality and high crystallinity. However, synthesizing large-area monolayer 2D superconductors has proven to be a daunting task as they tend to oxidize rapidly in the presence of air6.

In this study, a novel 'encapsulation epitaxy' technique is introduced, which enables the growth of large-area, air-stable monolayer niobium diselenide (NbSe2) films (1L-NbSe2) (1). This growth mechanism involves the pre-deposition of an encapsulation layer, such as graphene or hexagonal boron nitride, on a 3D substrate like SiO2 or Si3N4.

The encapsulation layer simultaneously acts as a template for the epitaxial growth of 1L-NbSe2 underneath it and as a protective capping layer against ambient degradation4.

The resulting 1L-graphene/NbSe2 heterostructures demonstrate robust superconductivity, with a superconducting transition temperature (Tc) of approximately 1 K1. Additionally, these heterostructures exhibit enhanced charge density waves (CDWs), with a CDW transition temperature (TCDW) of around 177 K1. The encapsulation epitaxy method also facilitates the integration of 1L-NbSe2 into superconducting circuits through oxidation-free transfer and superconducting edge-contact techniques4.

The 1L-NbSe2 in these circuits exhibits a measured kinetic inductance (LK) of approximately 0.7 nH□−1, making it suitable for quantum circuits that require elements with high kinetic inductance4.

This encapsulation-epitaxy methodology holds great promise for the wafer-scale, monolithic fabrication of superconducting quantum circuitry, as it enables the production of air-stable 2D superconductors and van der Waals heterostructures.