Education and Topological Electronics Donald Heiman, Northeastern University, DMR 0907007

1. Linear magnetoresistance in topological insulators:Quantum phase coherence effects at high temperaturesDonald Heiman, Northeastern University, DMR 0907007 Topological insulators (TIs) are semiconductors that can be insulating in the bulk, yet have metallic conducting surfaces. They have the remarkable property that the motion of electrons on these surfaces is tightly coupled to the direction of the electron spin. Novel Bi2Te2Se TI films have been fabricated on silicon substrates. In magnetoconductivity experiments we demonstrated that the quantum mechanical phase of moving electrons is retained even after many direction-changing collisions. This is manifest as a linear increase in the resistance for increasing magnetic field up to 14 tesla. We developed a model which shows that this phase coherence remains dominant up to temperatures approaching room temperature. Magnetoresistance of Bi2Te2Se for temperatures up to T=147 K. The solid curves are fits to our phase coherence model. Assaf, Cardinal, Wei, Katmis, Moodera and Heiman, Rev. Sci. Instrum. 83, 033904 (2012); Phys. Rev. B (submitted, 2012).

2. Education and Topological ElectronicsDonald Heiman, Northeastern University, DMR 0907007 The combination of spin-orbit coupling and time-reversal symmetry in Topological Insulators (TIs) leads to protected spin states on their surfaces and edges. Consequently, the surfaces have remarkable metallic conduction that is predicted to have many fascinating electronic properties. One of the extraordinary properties is that backscattering of electrons by nonmagnetic impurities is suppressed. TIs have many exceptional features that could have a decisive impact on future low-power electronics. The majority of the research on this project was carried out by a new graduate student, Badih A. Assaf. Through his hard work he is quickly becoming an expert in the field of topological insulators. An undergraduate, Tom Cardinal, made significant contributions to our understanding of the structure of these materials using X-ray diffraction.