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A New Theory on Crystal Symmetry May Lead to Advanced Applications

September 7, 2017

Angelo Mascarenhas and Brian Fluegel, scientists at the Energy Department’s National Renewable Energy Laboratory (NREL), have published a theory for crystal lattices with a tensor periodicity that may inspire a new generation of techniques for growing materials with properties that can be exploited for electronic, photonic, and optical energy-storage applications.

Their insights are published in "Ferroelastic modulation and the Bloch formalism," which appears in Science Advances. Lekhnath Bhusal, a former NREL post-doctoral researcher, was also an author.

To develop new advanced materials, it is essential to understand the relationship between the electronic structure of a material and its characteristic properties. This structure–property nexus has been used in epitaxial growth—depositing atomic layer upon atomic layer in an orderly manner—to design new electronic materials with desired properties. In fact, for almost half a century, advances in electronic and photonic technologies have relied on designing materials that incorporate such artificial scalar periodicities.

However, NREL scientists are studying synthetic crystal lattices that have "tensor" periodicity. "We have developed a new theory for electron and photon energy states in these lattices," Mascarenhas explains, "and a provocative aspect of our work is that it departs from Felix Bloch’s theory first developed in 1926 that laid the foundation for quantum mechanics applied to solid-state materials."

The NREL study reveals that these lattices can lead to spiral trajectories for conduction-band electrons, without external magnetic fields—an unusual feature that could be of interest for electronic applications. Furthermore, strongly localized and spiral states for photons can slow down the propagation of light. And to store light, a prism can be used to couple a laser beam into the lattice.

"This work actually started as part of my post-doctoral project many years ago, and I’m glad that we’ve been able to revisit this area of research and have finally developed and published this theory," Mascarenhas says.

The work was funded by DOE's Office of Science.

NREL is the U.S. Department of Energy's primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by The Alliance for Sustainable Energy, LLC.