Model electron spin
maps of the iron-tellurium-sulfur material. The left-hand column, a-c,
shows three models of
electron spin correlations, with the red and green colors
of the peaks and
corresponding planar projections below each model representing
oppositely oriented
spins. The images on the right, d-f, show the resulting neutron
scattering patterns
for each case. Starting at a, which represents the dominant
correlations at high
temperature, notice how the spins form alternating squares
like a checkerboard
in the planar projection, and how the "square dance partners"
of the pattern change
to diagonals in (b), which occurs on cooling to low temperature,
and finally to
alternating stripes stipulated to exist in a good superconductor (c).
Changes in short-range, transient order in competing
liquid-like phases precede onset of superconductivity
(August 6, 2015) Despite
a quarter-century of research since the discovery of the first high-temperature
superconductors, scientists still don't have a clear picture of how these
materials are able to conduct electricity with no energy loss. Studies to date
have focused on finding long-range electronic and magnetic order in the
materials, such as patterns of electron spins, based on the belief that this
order underlies superconductivity. But a new study published online the week of
August 3, 2015, in the Proceedings of the National Academy of Sciences is
challenging this notion.
The study, conducted by researchers from the U.S. Department
of Energy's (DOE) Brookhaven National Laboratory and Oak Ridge National Laboratory
(ORNL), describes how an iron-telluride material related to a family of
high-temperature superconductors develops superconductivity with no long-range
electronic or magnetic order when "doped" with a small amount of
sulfur. In fact, the material displays a liquid-like magnetic state consisting
of two coexisting and competing disordered magnetic phases, which appears to
precede—and may be linked to—its superconducting behavior.
Left to right:
Brookhaven physicists Igor Zaliznyak, Alexei Tsvelik, and Cedomir Petrovic
with models
representing electron spin correlations in an iron-based superconductor.
"Our results challenge a number of widely accepted
paradigms into how unconventional superconductors work," said the study's
lead researcher, Brookhaven physicist Igor Zaliznyak. "I believe that we
have uncovered an important clue to the nature of magnetism and its connections
to superconductivity in the iron-based superconductors."
This advance could open up a new avenue for exploring the
emergence of a property with great potential for widespread use. Conventional
superconductors, which must be chilled to extremely low temperatures to
operate, already play a key role in many modern technologies, from medical magnetic
resonance imaging (MRI) to maglev trains. New clues about the function of
unconventional superconductors, which do not need to be super-cooled, could
lead to many more technologies, including, potentially, zero-energy-loss power
transmission lines and other important energy applications. Indeed, other
materials based upon a similar structure as the material studied here can
operate as superconductors at these "warmer" temperatures, so
understanding the physics of this close relative has many important
implications.