Image courtesy of Brookhaven National Laboratory
In an iron-based superconductor, model patterns of electron spins show two competing liquid-like magnetic phases. (Positive spins correspond with yellow and red, while negative spins are green and black.) From the planar projection (below each model), a checkerboard pattern (top) of spins represents the liquid-like magnetic correlations at high temperature. Upon cooling near the superconductivity transition point, two fluctuating liquid-like magnetic states coexist: the original checkboard pattern and a new diagonal pattern (bottom).
Although electric current flow without resistance, or superconductivity, was discovered decades ago, the phenomenon has not been completely explained. There is a consensus that magnetism plays a key role in iron-based superconductors, but the details are controversial. Helping to make sense of recent observations, two distinct, liquid-like magnetic phases were discovered to coexist near the superconducting transition. Experiments on a superconductor revealed changing patterns of magnetic moments that are similar to the patterns formed by square dancers on a dance floor.
This discovery provides important clues to the nature of magnetism and its relationship to the enigmatic unconventional superconductivity in iron chalcogenides (e.g., FeTe0.86S0.13). This work could aid in creating a more complete theory for high-temperature superconductivity.
There are two classes of high-temperature superconductors: cuprates discovered in 1986 and iron-based compounds in 2006. Although high-temperature superconductivity (electric current flow without resistance) was discovered almost 30 years ago, a complete theory for this phenomenon has been elusive, even with the intense experimental and theoretical research by the large, world-wide condensed matter scientific community. While there is a consensus that magnetism plays an important role in the emergence of superconductivity in iron-based superconductors, the nature of the magnetism and its interaction with electrons remain controversial. Recently, researchers from Brookhaven National Laboratory discovered an unusual form of magnetism in a high-temperature iron-based superconductor close to its transition temperature. The magnetism has dynamic correlations like those in a liquid (their positions fluctuate in time) and spatial correlations that change with temperature. Inelastic and quasielastic neutron scattering experiments at Oak Ridge National Laboratory on a compound (FeTe0.86S0.13) that becomes superconducting upon cooling revealed dynamical arrangements of magnetic moments similar to the patterns formed by square dancers on a dance floor. As the temperature is reduced toward the critical temperature of the compound, dynamic exchange of electrons occurs between two liquid-like magnetic phases, eventually leading to the superconducting state. These results provide significant insights on the nature of magnetism and its connection to superconductivity in iron-based high temperature superconductors and could help in the development of a complete theory for high-temperature superconductivity.
Brookhaven National Laboratory
Brookhaven National Laboratory
This work was supported by the U.S. Department of Energy’s Office of Science (Office of Basic Energy Sciences), including support of the Center for Emergent Superconductivity, an Energy Frontier Research Center, and of the High Flux Isotope Reactor and Spallation Neutron Source, DOE Office of Science User Facilities.
I. A. Zaliznyak, A. T. Savici, M. Lumsden, A. M. Tsvelik, R. Hu, and C. Petrovic, “Spin-liquid polymorphism in a correlated electron system on the threshold of superconductivity.” Proceedings of the National Academy of Sciences United States of America 12, 10316 (2015). [arXiv:1502.06051v1]
BES, MSE, EFRCs
DOE Laboratory, SC User Facilities, BES User Facilities, HFIR, SNS