Prediction of Dirac Semimetal Arjun G. Yodh , University of Pennsylvania, DMR 1062638

1. Prediction of Dirac Semimetal Arjun G. Yodh, University of Pennsylvania, DMR 1062638 In two-dimensions (2D), graphene is a so-called topological insulator material which has been the focus of much recent research in physics. It is an insulator within its interior and a conductor on its perimeter. In the present research, we seek similar materials at the boundary between metals and insulators, but in 3D. A key feature of this new material is a Fermi surface with relativistic energy-momentum relationships for electron energy bands that come together at a single point, called the Dirac point, which is protected by symmetry. Our calculations suggest that the compound BiAl2O4,, formulated by substituting bismuth into the A site of the spinel crystal structure (MgAl2O4) has a band structure that contains a Dirac point (see Figure right). Prediction of a new 3D analog of graphene: Band structure of BiAl2O4.exhibits 4-fold linear band crossing at X. This Dirac point disperses linearly in all directions and should offer a material with high carrier mobility.

2. Prediction of Dirac Semimetal Arjun G. Yodh, University of Pennsylvania, DMR 1062638 We are proposing that crystalline solid, BiAl2O4, that we have identified should have electronic properties similar to graphene. It should be insulating in its bulk interior and conducting on its surface. Such a material is potentially interesting for electronics applications, perhaps even applications in quantum computing. This largely computational research takes a first step towards these applications. In order for this material to be used, however, we must first make it in the laboratory, which presents a new but clear challenge to experimentalists. Julia Steinberg is a rising junior in Physics at Penn who spent the summer working with Professor Andrew Rappe, Chemistry, as an REU student. She carried out the calculations that discovered the Dirac point in this class of material.