Mechanisms for adatom-induced disruption of Bi2Sr2CaCu2O8(001): Scanning-tunneling-microscopy studies of Ag-, Au-, and Cr-overlayer growth

On-Demand Local Modification of High-Tc Superconductivity in Few Unit-Cell Thick Bi2 Sr2 CaCu2 O8+δ

High-temperature superconductors (HTSs) are important for potential applications and for understanding the origin of strong correlations. Bi₂ Sr₂ CaCu₂ O_8+δ (BSCCO), a van der Waals material, offers a platform to probe the physics down to a unit-cell. Guiding the flow of electrons by patterning 2DEGS and oxide heterostructures has brought new functionality and access to new science. Similarly, modifying superconductivity in HTS locally, on a small length scale, is of immense interest for superconducting electronics. A route to modify superconductivity locally by depositing metal on the surface is reported here by transport studies on few unit-cell thick BSCCO. Deposition of chromium (Cr) on the surface over a selected area of BSCCO results in insulating behavior of the underlying region. Cr locally depletes oxygen in CuO₂ planes and disrupts the superconductivity in the layers below. This technique of modifying superconductivity is suitable for making sub-micrometer superconducting wires and more complex superconducting devices.

Direct-Write X-ray Nanopatterning: A Proof of Concept Josephson Device on Bi2Sr2CaCu2O8+δ Superconducting Oxide

We describe the first use of a novel photoresist-free X-ray nanopatterning technique to fabricate an electronic device. We have produced a proof-of-concept device consisting of a few Josephson junctions by irradiating microcrystals of the Bi2Sr2CaCu2O8+δ (Bi-2212) superconducting oxide with a 17.6 keV synchrotron nanobeam. Fully functional devices have been obtained by locally turning the material into a nonsuperconducting state by means of hard X-ray exposure. Nano-XRD patterns reveal that the crystallinity is substantially preserved in the irradiated areas that there is no evidence of macroscopic crystal disruption. Indications are that O ions have been removed from the crystals, which could make this technique interesting also for other oxide materials. Direct-write X-ray nanopatterning represents a promising fabrication method exploiting material/material rather than vacuum/material interfaces, with the potential for nanometric resolution, improved mechanical stability, enhanced depth of patterning, and absence of chemical contamination with respect to traditional lithographic techniques.

Doping change in the Bi-2212 superconductor directly induced by a hard X-ray nanobeam

We describe the controlled use of a 17 keV X-ray synchrotron nanobeam to progressively change the oxygen doping level in Bi-2212 superconducting whisker-like single crystals. Our data combine structural and electrical information collected on the same crystals, showing a maximum change in the critical temperature Tc of 1.3 K and a maximum elongation of ∼1 Å in the c-axis length, compared to the as-grown conditions. Simulations of our experimental conditions by means of a finite element model exclude local heating induced by the X-ray nanobeam as a possible cause for the change in the doping level and suggest an important role of secondary electrons. These findings support the possible use of hard X-rays as a novel direct-writing, photoresist-free lithographic process for the fabrication of superconducting devices, with potential nanometric resolution and 3D capability.