Evidence of Josephson Coupling in a Few-Layer Black Phosphorus Planar Josephson Junction

Abstract

Setting up strong Josephson coupling in van der Waals materials in close proximity to superconductors offers several opportunities both to inspect fundamental physics and to develop cryogenic quantum technologies. Here we show evidence of Josephson coupling in a planar few-layer black phosphorus junction. The planar geometry allows us to probe the junction behavior by means of external gates, at different carrier concentrations. Clear signatures of Josephson coupling are demonstrated by measuring supercurrent flow through the junction at milli-Kelvin temperatures. Manifestation of a Fraunhofer pattern with a transverse magnetic field is also reported, confirming the Josephson coupling. These findings represent evidence of proximity Josephson coupling in a planar junction based on a van der Waals material beyond graphene and will expedite further studies, exploiting the peculiar properties of exfoliated black phosphorus thin flakes.

Propagation of visible light in nanostructured niobium stripes embedded in a dielectric polymer

“…After the sputtering process, the sample underwent a fast lift-off in acetone at 55 • C. Then it was immediately coated with a bilayer of copolymer methyl methacrylate (8.5) methacrylic acid (MMA (8.5) MAA) and PMMA, to guarantee protection from oxidation. This protection layer is approximately 700 nm thick, with 450 nm of copolymer and 250 nm of PMMA on top [32]. For the sample with Cr/Au stripes, after the oxygen plasma the sample was transferred into a thermal evaporator, and a 10 nm/65 nm Cr/Au bilayer was deposited.…”

“…Besides, niobium is thus a very versatile platform, and it is recently receiving increasing attention in the quantum technology community, due to its high critical field (Hc ∼ 2 T) and critical temperature (Tc ∼ 9.2 K) [25]. High quality Josephson junctions based on Nb superconducting contacts were recently fabricated with different materials on the normal region, such as III-V semiconductors [26][27][28][29][30] and 2D materials [31,32], demonstrating good proximity effect and high transparency of interfaces.…”

Scanning gate microscopy imaging of the supercurrent distribution in a planar Josephson junction

“…The junction dimensions are defined by the width (W ) and the length (L) of the semiconducting region. In experimental realizations, such planar junctions have been defined in InAs 10-15 , HgTe 16 , bP 17 , graphene [36][37][38][39] , InSb 18 or InAsSb 19 quantum wells, and InSb nanoflakes [20][21][22] interfaced with aluminum or niobium superconducting contacts. The supercurrent (visualized in orange in Fig.…”

“…The length of the normal part can be of the order of hundreds of nanometers [10][11][12]15,17,18,22 due to fabrication techniques or the requirements of the SGM method itself, i.e., the fact that the SGM tip has to be able to fit between the superconductors, setting the lower bound to the normal part length. This combined with large induced gaps when using, e.g., Nb as the superconductor leads to structures that can exceed the short-junction approximation.…”

“…Here we theoretically explore the possibility of a direct visualization of the supercurrent distribution and the associated formation of Josephson vortices by a combination of critical current measurements and the scanning gate microscopy (SGM) technique. Our idea exploits the fact that in planar SNS junctions [10][11][12][13][14][15][16][17][18][19][20][21][22] the normal plane between the superconductors remains exposed, which opens the possibility for the application of the SGM technique that has been used successfully for over two decades for imaging of normal current flows. SGM in normal systems is a widely used technique which relies on measuring the conductance when a biased atomic force microscope tip scans over the device, inducing a repulsive potential in the two-dimensional electron gas (2DEG) of the sample and affecting the paths of the propagating electrons.…”