Argonne, UChicago Scientists Open Doors to Emergent Magnetism

Quantum criticality in chromium is a stand-in for more complex systems

ARGONNE, Ill. (June 18, 2009) — Scientists at the U.S. Department of Energy's Argonne National Laboratory and the University of Chicago have reached a milestone in the study of emergent magnetism.

Funding for this research was provided by the National Science Foundation Division of Materials Research and the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

Studying simple metallic chromium, the joint UChicago-Argonne team discovered a pressure-driven quantum critical regime and achieved the first direct measurement of a "naked" quantum singularity in an elemental magnet. The team was led by University of Chicago scientist Rafael Jaramillo, working in the group of Thomas Rosenbaum, and Argonne scientist Yejun Feng of the Advanced Photon Source.

The sophisticated spin and charge order in chromium is often used as a stand-in for understanding similar phenomena in more complex materials, such as correlated oxides near a quantum critical point.

"Chromium is a simple metallic crystal that exhibits a sophisticated form of antiferromagnetism," said Jaramillo. "The goal was to find a simple system."

Quantum criticality describes a continuous phase transition that is driven by quantum mechanical fluctuations and is thought to underlie several enigmatic problems in condensed matter physics, including high-temperature superconductivity. However, achieving a continuous quantum phase transition in a simple magnet has proved challenging—the critical behavior in all systems studied to date has been obscured by competing phenomena. The discovery of a "naked" transition in simple chromium metal, therefore, paves the way for a more detailed understanding of magnetic quantum criticality

Like many elements, chromium has been extensively studied for decades, and a discovery of this magnitude in an element is particularly important.

"It's not often that you find out something new in an element," Feng said.

The pressure scale and experimental techniques required to measure quantum criticality in chromium necessitated extensive technical development at both Argonne and the University of Chicago. The resulting techniques for high-precision measurement of condensed matter systems at high pressure, developed for use at the Advanced Photon Source, now approach a level of precision and control comparable to more conventional techniques such as magnetic varying field and temperature.

This work was reported in the May 21 issue of the journal Nature.

Funding for this research was provided by the National Science Foundation Division of Materials Research and the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America 's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science.

Source: Argonne