A superconductor in a magnetic field acquires a finite electrical resistance caused by vortex motion. A quest to immobilize vortices and recover zero resistance at high fields made intense studies of vortex pinning one of the mainstreams of superconducting research. Yet, the decades of efforts resulted in a realization that even promising nanostructures, utilizing vortex matching, cannot withstand high vortex density at large magnetic fields. Here, we report a giant reentrance of vortex pinning induced by increasing magnetic field in a W-based nanowire and a TiN-perforated film densely populated with vortices. We find an extended range of zero resistance with vortex motion arrested by self-induced collective traps. The latter emerge due to order parameter suppression by vortices confined in narrow constrictions by surface superconductivity. Our findings show that geometric restrictions can radically change magnetic properties of superconductors and reverse detrimental effects of magnetic field.

Silicon-on-isolator-nanowires (SOI-NWs) were used for the label-free, real-time biospecific detection of the hepatitis B marker HBsAg and cancer marker α-fetoprotein (AFP). Specific protein-protein recognition was carried out using individual NWs that were functionalized with antibodies. To solve the problem of non-specific binding of target protein molecules to the sensor element the use of a reference NW with immobilized antibodies against non-target proteins was proposed. Using individual SOI-NW surface functionalization allowed the fabrication of a NW array, containing working NWs and reference NWs within one chip. It was shown that this approach allows us to reach a detection limit up to 10(-14) and 10(-15) M for HBsAg and AFP, respectively. Our investigations also allowed us to reveal the influence of the charged state of the target protein molecules and antibodies in solutions with various pH values on the target protein detection limit. A high sensitivity NW-detector is of interest for the creation of diagnosticums for hepatitis B and for the early stages of cancer diseases.

The properties of silicon-on-insulator nanowires (SOI NWs) fabricated by means of electron lithography and gas etching of SOI in XeF 2 or SF 6 :CFCl 3 have been investigated. The method used to fabricate the nanowires was found to require no additional anneal to be given to the final structure for defect removal after nanostructuring. The sensitivity of SOI NWs to negative protein BSA molecules in the pH 7.4 buffer solution was shown to be as high as 1 femtomoles. The gate characteristics of SOI NWs were used to determine the charge density of particles adsorbed on the NW surface. A charge density of 4.6 × 10 11 cm −2 was estimated for a 1 femtomole protein concentration. The combined use of open-channel structures with top gates was employed for determining the charge state of structure surfaces after different chemical treatments. Chemical treatments giving rise to a density of the negative charges on the surface of NWs ranging in the interval (7-23) × 10 11 cm −2 were examined. Treatments in methanol (after removal of the native oxide) were found to provide stabilization of the SOI surface over a 3-h interval after the treatments.

We present the results of the comparative study of the influence of disorder on transport properties in continuous and nanoperforated TiN films. We show that nanopatterning turns a thin TiN film into an array of superconducting weak links and stimulates both, the disorder-and magnetic field-driven superconductor-to-insulator transitions, pushing them to lower degree of disorder. We find that nanopatterning enhances the role of the two-dimensional Coulomb interaction in the system transforming the originally insulating film into a more pronounced insulator. We observe magnetoresistance oscillations reflecting collective behaviour of the multiconnected nanopatterned superconducting film in the wide range of temperatures and uncover the physical mechanism of these oscillations as phase slips in superconducting weak link network.That a thin film of the same material can be a superconductor but can very well turn an insulator, is one of the most remarkable aspects of disordered superconductors [1][2][3][4][5][6][7]. The engine driving the transition between the superconducting and insulating states is disorder the effect of which is two-fold. On the one hand, disorder limits the electron diffusion enhancing thus the Coulomb electron-electron interaction which competes with the Cooper pairing [8,9]. The latter in an interplay with the disorder-induced inhomogeneities localizes Cooper pairs to form an insulating state, Cooper-pair insulator. A restricted geometry is critical to effects of disorder -for the insulating state to be observed the superconducting material is to be thinned down till its thickness d becomes comparable to or smaller than the superconducting coherence length ξ. One of the major experimental challenges in these studies remains the optimization of material parameters taking it to the closest proximity of the direct superconductor-insulator transition and identifying the systems that exhibit such a transition at available temperatures. In this Letter we meet this challenge via creating a metamaterial with the desirable properties, the multiconnected thin superconducting film. We show that nanopatterning a thin TiN film into a regular sievelike configuration turns it into an array of weak links and, therefore, stimulates the direct superconductor-toinsulator transition. Depending on the original degree of disorder it either suppresses the critical temperature T c , or drives the initially superconducting film into an insulating state, or else, transforms the originally insulating film into an even more pronounced insulator.As a starting material we have chosen a 5 nm thin TiN film which was identical by its parameters to those that experienced the superconductor-insulator transition after soft plasma etching [10][11][12][13] and which were fully characterized by the high resolution electron beam, infrared [14], and low-temperature scanning tunnelling spectroscopy [15]. The smooth, continuous, and uniform TiN film was formed on the Si/SiO 2 substrate by atomic layer deposition. The film had the super...

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