This visual representation of neutron data from ORNL’s Spallation Neutron Source shows the evolution of spin waves as a function of increasing energy for the iron chalcogenide FeTe. Experiments indicate high-temperature superconductivity in different materials may share a common magnetic origin. Credit: Oak Ridge National Laboratory
Neutron scattering analysis of two families
of iron-based materials suggests that the magnetic interactions thought
responsible for high-temperature superconductivity may lie “two doors
down”: The key magnetic exchange pairings occur in a next-nearest-neighbor
ordering of atoms, rather than adjacent atoms.
Researchers at the Department of Energy’s
Oak Ridge National Laboratory and the Univ.
of Tennessee, using the Spallation
Neutron Source’s ARCS
Spectrometer, performed spin-wave studies of magnetically ordered iron
chalcogenides. They based their conclusions on comparisons with previous
spin-wave data on magnetically ordered pnictides, another class of iron-based
“As we analyze the spectra, we find
that even though the nearest neighbor exchange couplings between chalcogenide
and pnictide atoms are different, the next nearest neighbor exchange couplings
are closely similar,” said Pengcheng Dai, who has a joint appointment with
ORNL’s Neutron Sciences Directorate and the Univ. of Tennessee.
Dai referred to theories that have suggested
second-nearest-neighbor couplings could be responsible for the widely acclaimed
but poorly understood properties of high-temperature superconductors.
“There are theories suggesting that
it’s the second nearest neighbor that drives the superconductivity,” he
said. “Our discovery of similar next-nearest-neighbor couplings in these
two iron-based systems suggests that superconductivity shares a common magnetic
Oliver Lipscombe of the Univ. of Tennessee, Dai and
ORNL’s Doug Abernathy used the ARCS time-of-flight instrument on the SNS to
study spin waves of the chalcogenide iron-tellurium superconductor and compared
these with iron pnictide superconductors. Scientists have been studying the
iron-based superconductors since their discovery in 2008 to see if the dynamics
behind their high-temperature superconducting properties—in which electricity
flows without resistance at temperatures well above absolute zero—could help
explain what was until recently thought to be exclusive to copper-oxide-based
“Finding commonalities is always a good
step when you’re looking for a very basic understanding of a phenomenon like
high-temperature superconductivity,” said Abernathy, who is lead
instrument scientist for the ARCS instrument.
The team’s neutron scattering analysis of
the materials was made possible by the high intensity of the neutron beams
provided by the SNS, which is the world’s most powerful pulsed neutron source.
Neutrons, which carry no electric charge but can act as subatomic magnets, are
well suited for studying atom-scale spin characteristics.
“Since the interactions in the
high-temperature superconductors are so strong, measurement of these materials’
spin waves requires beams of energetic neutrons that were unavailable to the
research community at this intensity before the SNS,” Abernathy said.
The work, which was funded by the DOE Office
of Science, is published in Physical