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Microscope image of a magnetic field in a thallium-copper-oxide
high-temperature
superconductor. This magnetic field is generated in response to the
movement of
particles which carry electric current without resistance in the
superconductor. Using a
special device known as a SQUID microscope which can detect and
measure tiny
magnetic fields, IBM researchers determined that the strength of the
magnetic field
(represented by the height of the peak in the image) to be equal to half of
a number
known as a flux quantum. The half-flux quantum value agrees with the
notion that the
particle pairs are "d-wave" in nature, which means among other things
that the
pairs are forbidden to flow along certain directions in the
crystal.
This research was described in Nature 387, 481 (1997)