CAREER: New Materials in Condensed Matter PhysicsIan R. Fisher, Stanford University, DMR-0134613

Magnetic phase diagram of BaCuSi2O6, showing (in yellow) the ordered magnetic state. Inset shows a schematic diagram of the crystal structure, comprising well-separated vertical Cu dimers.

Nature 441, 617 (2006); PRB 73, 100407(R) (2006); PRB 72, 100404(R) (2005); PRB 71, 212405 (2005); Cond-mat/0606244; Cond-mat/0607465

The development of new materials with unconventional properties plays a central role in condensed matter physics. In this instance, we have studied the high field behavior of a very old material that is new to the world of physics – Han purple, or BaCuSi2O6. The material is a “spin dimer” compound (i.e. comprises pairs of magnetic ions). We find that that the magnetic properties show a remarkable “dimensional reduction” at the lowest temperatures. Our results have implications for materials beyond just this specific compound.

Fits to the phase boundary yield critical exponents characteristic of the BEC universality class. These exponents show a cross-over from 3D to 2D behavior on cooling below approximately 1 K.

The first step in studying a new material is one of synthesis – a particular specialty of our research group. A broader impact of our research is the availability of single crystals of new materials for collaborative projects with US National Laboratories and universities.

The photographs show single crystals of some of the complex oxides and intermetallics that we have developed as part of this CAREER award. In many cases these are new materials for which the magnetic and electronic properties were either unknown or poorly understood.

More information:http://www.stanford.edu/group/fisher

CAREER: New Materials in Condensed Matter PhysicsIan R. Fisher, Stanford University, DMR-0134613

BaCuB2O5

BaCuSi2O6

R-Mg-Cd Al-Pd-Re Tb6Mo4Al43

Ba2OsNaO6

Sr2Cu(BO3)2 Ba2Cu(BO3)2

BaCu2Si2O7