Measurements taken* at the National
Institute of Standards and Technology (NIST) may help physicists develop
a clearer understanding of high-temperature superconductors, whose behavior
remains in many ways mysterious decades after their discovery. A new copper-based
compound exhibits properties never before seen in a superconductor and could
be a step toward solving part of the mystery.
Copper-based high-temperature superconductors are created by taking a nonconducting
material called a Mott insulator and either adding or removing some electrons
from its crystal structure. As the quantity of electrons is raised or lowered,
the material undergoes a gradual transformation to one that, at certain temperatures,
conducts electricity utterly without resistance. Until now, all materials that
fit the bill could only be pushed toward superconductivity either by adding
or removing electrons—but not both.
However, the new material tested at the NIST Center for Neutron Research (NCNR)
is the first one ever found that exhibits properties of both of these regimes.
A team of researchers from Osaka University, the University of Virginia, the
Japanese Central Research Institute of Electric Power Industry, Tohoku University
and the NIST NCNR used neutron diffraction to explore the novel material, known
only by its chemical formula of YLBLCO.
The material can only be made to superconduct by removing electrons. But if
electrons are added, it also exhibits some properties only seen in those materials
that superconduct with an electron surplus—hinting that scientists may
now be able to study the relationship between the two ways of creating superconductors,
an opportunity that was unavailable before this “ambipolar” material
The results are described in detail in a “News and Views” article
in the August, 2010, issue of Nature Physics, “Doped Mott insulators:
Breaking through to the other side.”**
* K. Segawa , M. Kofu, S.-H. Lee, I. Tsukada. H. Hiraka, M. Fujita, S. Chang,
K. Yamada and Y. Ando. Zero-Doping State and Electron-Hole Asymmetry in an Ambipolar
Cuprate. Nature Physics, August 2010, pp. 579-583, DOI 10.1038/NPHYS1717.
** J. Orenstein and A. Vishwanath. Doped Mott insulators: Breaking through
to the other side. Nature Physics, V. 6, August, 2010. DOI:10.1038/nphys1751.