Closing the superconducting gap in small Pb nanoislands with high magnetic fields

Abstract

Superconducting properties change in confined geometries. Here we study the effects of strong confinement in nanosized Pb-islands on Si(111) 7×7. Small hexagonal islands with diameters less than 50 nm and a uniform height of 7 atomic layers are formed by depositing Pb at low temperature and annealing at 300 K. We measure the tunneling spectra of individual Pb-nanoislands using a low-temperature scanning tunneling microscope operated at 0.6 K, and follow the narrowing of the superconducting gap as a function of magnetic field. We find the critical magnetic field, at which the superconducting gap vanishes, reaches several Tesla, which represents a greater than 50-fold enhancement compared to the bulk value. By independently measuring the size of the superconducting gap, and the critical magnetic field that quenches superconductivity for a range of nanoislands we can correlate these two fundamental parameters and estimate the maximal achievable critical field for 7 ML Pb-nanoislands to 7 T.

Disorder‐Induced Quantum Griffiths Singularity Revealed in an Artificial 2D Superconducting System

“…[ 27,28 ] Then, 20‐nm‐thick Pb was deposited on single‐crystalline graphene by electron beam evaporation (Experimental Section; Figure S2, Supporting Information). Owing to the poor wettability of graphene [ 8,11 ] and the low melting point of Pb, [ 29,30 ] the deposited Pb is prone to being randomly distributed into irregular disconnected nanoislands, as suggested by cross‐sectional transmission electron microscopy (TEM, Figure a) and plan‐view scanning electron microscopy (SEM) in Figure 1b. TEM–energy dispersive X‐ray spectroscopy (TEM–EDS, Figure 1d) further proves that Pb nanoislands are completely disconnected from each other.…”

Quasireentrant superconductivity and enhanced critical field in thick Pb‐SiO2 granular films

“…Over the past three decades, great interests have been focused on the electronic transport properties of granular composites consisting of superconductors and insulators . The interests were firstly aroused by the enhancement of the superconducting transition temperature and critical magnetic field of nanostructured superconducting materials .…”

Hydrogen‐Intercalated Graphene on SiC as Platform for Hybrid Superconductor Devices

“…This behavior generally can be fitted by a function as derived from the Ginzburg–Landau theory [ 50 ] and yields with nm T. A similar value has been reported for Pb islands on Si(111) for a range of smaller diameters, although the authors modify the function to to account for an effective superconducting area slightly different to the topographic one. [ 61 ] In the present study, the diameter independent offset is fitted to nm with nm T. However, the deviation remains small compared to the observed spread of critical fields. We do not observe vortex formation in our measurements up to effective diameters of ≈70 nm (see Figure S3c–f, Supporting Information, for more details about Δ and B c as function of island size).…”