Topological Spintronics: From the Haldane Phase to Spin Devices
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 . Inappropriately 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].
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