There’s a literal disturbance in the force that alters what physicists have long thought of as a characteristic of superconductivity, according to Rice University scientists.
Rice physicists Pengcheng Dai and Andriy Nevidomskyy and their colleagues used simulations and neutron scattering experiments that show the atomic structure of materials to reveal tiny distortions of the crystal lattice in a so-called iron pnictide compound of sodium, iron, nickel, and arsenic.
These local distortions were observed among the otherwise symmetrical atomic order in the material at ultracold temperatures near the point of optimal superconductivity. They indicate researchers may have some wiggle room as they work to increase the temperature at which iron pnictides become superconductors.
The discovery reported this week in Nature Communications is the result of nearly two years of work by the Rice team and collaborators in the U.S., Germany, and China.
Dai and Nevidomskyy, both members of the Rice Center for Quantum Materials (RCQM), are interested in the fundamental processes that give rise to novel collective phenomena like superconductivity, which allows materials to transmit electrical current with no resistance.
Scientists originally found superconductivity at ultracold temperatures that let atoms cooperate in ways that aren’t possible at room temperature. Even known “high-temperature” superconductors top out at 134 Kelvin at ambient pressure, equivalent to minus 218 degrees Fahrenheit.
So if there’s any hope for widespread practical use of superconductivity, scientists have to find loopholes in the basic physics of how atoms and their constituents behave under a variety of conditions.
That is what the Rice researchers have done with the iron pnictide, an “unconventional superconductor” of sodium, iron, and arsenic, especially when doped with nickel.
To make any material superconductive, it must be cooled. That sends it through three transitions: First, a structural phase transition that changes the lattice; second, a magnetic transition that appears to turn paramagnetic materials to antiferromagnets in which the atoms’ spins align in alternate directions; and third, the transition to superconductivity. Sometimes the first and second phases are nearly simultaneous, depending on the material.
thumbnail courtesy of phys.org