Physicists in the US have made a quantum interference device by coating a pair of DNA molecules with superconducting material. The resulting two-nanowire device also showed unusual resistance oscillations in an applied magnetic field (Science 308 1762).
Alexey Bezryadin and colleagues at the University of Illinois at Urbana-Champaign made the devices by arranging two DNA molecules across a trench about 100 nm wide that had been etched into silicon nitride and silicon dioxide layers on a silicon chip. The DNA molecules and the substrate were then sputter-coated with an alloy of molybdenum and germanium (Mo21Ge79).
The resulting nanowires became superconducting at low temperatures, with their resistance decreasing exponentially with temperature. As is typical for nanowires, they did not exhibit zero resistance.
The team built the device to search for phenomena known as Little-Parks oscillations but they found something completely different. In the absence of a magnetic field, the wires exhibited a nonzero resistance over a broad temperature range. However, when a magnetic field was present, the device showed regular and unexpected oscillations of resistance with the magnetic field. To investigate the effect, the researchers tested devices with different geometries, varying the width of the current leads and the spacing between the wires.
“The applied magnetic field causes a small current to flow along the trench banks, and this current then causes a large change in resistance,” explained team member Paul Goldbart. “The strength of the current is controlled only by the magnetic field and the width of the banks supporting the wires.”
The researchers say their device is very sensitive to magnetic fields and, if coupled to a scanning probe microscope, can be used to detect local variations in magnetic field. It could also be used as a gradiometer to measure properties of the order parameter in superconductors.
