Studying simple metallic chromium, the joint UC-Argonne team has discovered
a pressure-driven quantum critical regime and has 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
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 proximate to 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
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 to be a challenging goal, as 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
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 Sector 4 of 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 is 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.
Posted June 18th, 2009