6 research outputs found
Magnetic flux periodicity of h/e in superconducting loops
The magnetic flux periodicity of superconducting loops as well as flux
quantization itself are a manifestation of macroscopic quantum phenomena with
far reaching implications. They provide the key to the understanding of many
fundamental properties of superconductors and are the basis for most bulk and
device applications of these materials. In superconducting rings the electrical
current has been known to periodically respond to a magnetic flux with a
periodicity of . Here, the ratio of Planck's constant and the
elementary charge defines the magnetic flux quantum . The well-known
periodicity is viewed to be a hallmark for electronic pairing in
superconductors and is considered evidence for the existence of Cooper pairs.
Here we show that in contrast to this long-term belief, rings of many
superconductor bear an periodicity. These superconductors include
the high- cuprates, SrRuO, the heavy-fermion superconductors,
as well as all other unconventional superconductors with nodes in the energy
gap functions, and s-wave superconductors with small gaps or states in the gap.
As we show, the 50-year-old Bardeen--Cooper--Schrieffer theory of
superconductivity implies that for multiply connected paths of such
superconductors the ground-state energies and consequently also the
supercurrents are generically periodic. The origin of this
periodicity is a magnetic-field driven reconstruction of the condensate and a
concomitant Doppler-shifted energy spectrum. The robust, flux induced
reconstruction of the condensate will be an important aspect to understand the
magnetic properties of mesoscopic unconventional superconductors.Comment: To appear in Nature Physics (2008). The new version has the same main
text and figures but also includes the supplementary material with a short
Appendix A on the "Numerical Method" and a longer Appendix B on an analytical
"Multichannel Model for Large D-Wave Rings
Ordering and manipulation of the magnetic moments in large-scale superconducting π-loop arrays
Since the discovery of high-transition-temperature (high-Tc) superconductivity in layered copper oxides1, many researchers have searched for similar behaviour in other layered metal oxides involving 3d-transition metals, such as cobalt and nickel. Such attempts have so far failed, with the result that the copper oxide layer is thought to be essential for superconductivity. Here we report that NaxCoO2dotyH2O (x 0.35, y 1.3) is a superconductor with a Tc of about 5 K. This compound consists of two-dimensional CoO2 layers separated by a thick insulating layer of Na+ ions and H2O molecules. There is a marked resemblance in superconducting properties between the present material and high-Tc copper oxides, suggesting that the two systems have similar underlying physic