We provide a perspective on the recent emergence of “topological spintronics,” which relies on the existence of helical Dirac electrons in condensed matter. Spin‐ and angle‐resolved photoemission spectroscopy shows how the spin texture of these electronic states can be engineered using quantum tunneling  or by breaking time‐reversal symmetry . In appropriately designed systems, broken time‐reversal symmetry transforms helical Dirac states into chiral edge states, a realization of Haldane’s Chern insulator phase of matter. This is characterized by a precisely quantized Hall conductance and dissipationless edge transport without a magnetic field. We show how these edge states can be quantitatively characterized by analyzing their giant anisotropic magnetoresistance . At miilikelvin temperatures, the interplay between Chern states and disordered magnetism  results in surprising behavior, perhaps consistent with quantum tunneling out of a ‘false vacuum’ . Finally, we show how these helical Dirac electrons provide a possible pathway toward a spin device technology that works at room temperature [6,7].
Nitin Samarth is Professor and Associate Head in the Physics Department at The Pennsylvania State University. He completed his undergraduate education in physics at the Indian Institute of Technology (Bombay) and received a Ph.D. in physics from Purdue University. He joined Penn State University after postdoctoral research at the University of Notre Dame. His research centers on the synthesis and study of semiconductor and magnetic quantum structures with a view towards applications in spintronics and quantum information. His group has particular interest in understanding the transport and dynamics of spins in semiconductor systems at length scales ranging from the nanoscale to the mesoscopic. Dr. Samarth is a Fellow of the American Physical Society and a recipient of the Faculty Scholar Medal in Physical Sciences at Penn State.
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