A useful pyramid scheme

Abstract

Viewpoint: A useful pyramid scheme Robert J. Cava, Department of Chemistry, Princeton University, NJ 08544, USA Published January 24, 2011 | Physics 4, 7 (2011) | DOI: 10.1103/Physics.4.7 Successful legwork to find a new insulator for spintronics applications sends a material running up the ladder of research and development. Demonstration of molecular beam epitaxy and a semiconducting band structure for I-Mn-V compounds T. Jungwirth, V. Novák, X. Martí, M. Cukr, F. Máca, A. B. Shick, J. Mašek, P. Horodyská, P. Němec, V. Holý, J. Zemek, P. Kužel, I. Němec, B. L. Gallagher, R. P. Campion, C. T. Foxon, and J. Wunderlich Phys. Rev. B 83, 035321 (2011) Published January 24, 2011 +Enlarge image Figure 1 Credit: Alan Stonebraker Figure 1 The principle of “derivative structures” in solid-state chemistry, with examples relevant to electronic materials. (Top) The familiar salt and diamond structures (the latter describing silicon) are themselves derived from the simpler face-centered cubic (fcc) structure. (Middle) The III-V crystal structure of GaAs derives from Si by placing different atoms in the fcc and tetrahedral positions, and the LiZnAs structure (describing several small-band-gap thermoelectrics) derives from NaCl by filling half of the tetrahedral voids. (Bottom) The CuInSe2 structure of semiconductors used in photovoltaic cells is derived from GaAs by replacing Ga with an ordered arrangement of Cu and In and the structure of MnCu2Sn (important for half metallic ferromagnets and superconductors) is derived from the LiZnAs structure by filling the remainder of the tetrahedral voids. Finally, LiMnAs (Jungwirth et al.) can be derived from either GaAs or LiZnAs. At every step in the derivative pathway, the added chemical degrees of freedom offer more means to tune the electronic properties. All our electronics technologies have, at their heart, critical materials that make their function possible. These can be “old” materials such as silicon, whose major materials development was achieved by previous generations, or “new” materials such as gallium-nitride, which has been developed by our contemporaries (Fig. 1). The impact of these two materials on society is, and will be, immeasurable, as are the contributions of many other materials in technologies that range from medical imaging to portable electronics. If the discovery and development of new materials comes to a stop, then the introduction and growth of new technologies will almost certainly come to a halt as well. Spintronics is an example of such a critical current technology, driving the creation of increased density, faster electronic memories through the electronic manipulation of magnetic moments. In a paper published in Physical Review B [1], Tomas Jungwirth and collaborators from the Institute of Physics of the Academy of Sciences of the Czech Republic, and collaborators from the Czech Republic and the United Kingdom, report the successful growth and characterization of LiMnAs, a new candidate material for spintronic applications.