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Physics treasure hidden in a wallpaper pattern

A newly identified insulating material using the symmetry principles behind wallpaper patterns may provide a basis for quantum computing, according to an international team of researchers. This strontium-lead sample (Sr2Pb3) has a fourfold Dirac cone surface state, a set of four, two-dimensional electronic surface states that go away from a point in momentum space in straight lines.

An international team of scientists has discovered a new, exotic form of insulating material with a metallic surface that could enable more efficient electronics or even quantum computing. The researchers developed a new method for analyzing existing chemical compounds that relies on the mathematical properties like symmetry that govern the repeating patterns seen in everyday wallpaper.

"The beauty of topology is that one can apply symmetry principles to find and categorize materials," said B. Andrei Bernevig, a professor of physics at Princeton.

The research, appearing July 20 in the journal Science, involved a collaboration among groups from Princeton University, the University of Pennsylvania (Penn), Sungkyunkwan University, Freie Universität Berlin and the Max Planck Institute of Microstructure Physics.

The discovery of this form of lead-strontium (Sr2Pb3) completes a decade-long search for an elusive three-dimensional material that combines the unique electronic properties of two-dimensional graphene and three-dimensional topological insulators, a phase of matter discovered in 2005 in independent works by Charles Kane at Penn and Bernevig at Princeton.

Some scientists have theorized that topological insulators, which insulate on their interior but conduct electricity on their surface, could serve as a foundation for super-fast quantum computing.

"You can think about a topological insulator like a Hershey's kiss," said Kane, a corresponding author on the paper. "The chocolate is the insulator and the foil is a conductor. We've been trying to identify new classes of materials in which crystal symmetries protect the conducting surface. What we've done here is to identify the simplest kind of topological crystalline insulator."