Anomalous correlated electron phenomena in Yb 2 Fe 12 P 7 M. Brian Maple, University of California-San Diego, DMR 0802478 Temperature – magnetic field.

Anomalous correlated electron phenomena in Yb2Fe

12P

7

M. Brian Maple, University of California-San Diego, DMR 0802478

Temperature – magnetic field phase diagram where the ordering temperatures taken from measurements of specific heat (cyan circles) and electrical resistivity (red circles) are superimposed on a contour plot which quantifies the degree of deviation from Fermi liquid behavior (for which “n” = 2).

X-ray diffraction data for single crystals of Yb

2Fe

12P

7.

The crystals were grown by undergraduate students in our lab using a technique known as the flux growth method. By Using a low melting point material as a flux, the melting point of the constituents comprising the desired material is reduced, and single crystals form within the melt.

For regular metals, conduction electrons behave as though they are completely noninteracting. However, it has been shown that in some compounds (mostly cerium and uranium based), the electron interactions can be extremely strong, leading to profound deviations from conventional metal (“Fermi liquid”) behavior. For instance, strongly interacting electrons can behave as though their masses are 100-1000 times that of a free electron. In other instances, as for the cuprates and iron pnictides, high temperature superconductivity is observed.

A long standing challenge in this field is that there are few examples of ytterbium-based compounds which exhibit tunable correlated electron behavior, even though ytterbium is widely regarded as being analogous to cerium.

We recently made the first observation of several types of highly anomalous behavior in high quality single crystal specimens of the compound Yb

2Fe

12P

7 where we found:

(1) An ordered ground state (likely antiferromagnetic) for temperatures less than 0.9 K, which is suppressed towards zero temperature with an applied magnetic field.(2) A large electronic mass (1200 X free electron mass) which is suppressed with an applied magnetic field.(3) Magnetic field tuned deviations from Fermi liquid behavior which extend to unprecedentedly high values of magnetic field.

Taken together, our results reveal that Yb2Fe

12P

7 is distinctly

different from other compounds of this type, suggesting that these phenomena may open up a new category of correlated electron behavior.

Anomalous correlated electron phenomena in Yb2Fe

12P

7

M. Brian Maple, University of California-San Diego, DMR 0802478

Education

Individuals at different stages of their careers (an assistant professor, three postdocs, a graduate student, four undergraduates – including one who participated in the research experience for undergraduate [REU] program, and a Quantum Design Inc. research scientist) have been involved in this ongoing research. Ryan Baumbach and James Hamlin, continue to work on the project (currently performing investigation of the effects of Co doping), several of the undergraduate students are still with us in the lab. Pei-Chun Ho, currently an assistant professor at California State University, Fresno, is pursuing related research projects.

Outreach

Our lab has a strong commitment to increasing awareness and understanding of the importance of experimental physics to a variety of communities. We currently teach an advanced physics lab (Phys 133) at the University of California, San Diego, where students are required to plan and carry out a research project, and then present the results to their peers in the class. Additionally, each year we perform regularly scheduled demonstrations at nearby elementary schools displaying some of the interesting aspects of low temperature physics (including the behavior of different materials when they are cooled to 77 K with liquid nitrogen).

Top: Graduate student Colin McElroy discusses the magnetic properties of liquid oxygen with students from Sweetwater High School during an April 2009 open house. Bottom: Masters students Kevin Huang and Eileen Gonzales and postdoc Ryan Baumbach demonstrate the characteristics of liquid nitrogen to students at Del Mar Pines elementary school at Science Day 2008.