Physics Colloquium: Nitin Samarth

September 25, 2018 @ 3:45 pm – 4:45 pm
1080 Physics Research Building (Smith Seminar Room)
191 W Woodruff Ave
Columbus, OH 43210
We provide a perspective on the recent emergence of “topological spintronics,” which relies on helical Dirac electrons on the surfaces of solids with strong spin-orbit coupling [1]..When timereversal symmetry is broken by ferromagnetic order, the helical Dirac states transition to chiral edge states [2]. This is a realization of Haldane’s Chern insulator phase of matter, characterized by a precisely quantized Hall conductance and ballistic edge transport without a magnetic field, even in systems with significant electronic and magnetic disorder [3,4]. The interplay between these edge states, dissipative channels and magnetic order appears to yield a condensed matter realization of quantum tunneling out of a ‘false vacuum’ [4]. Interesting opportunities are also emerging for patterning and manipulating the edge states using optical techniques [5]. On a more pragmatic note, the helical spin texture of the surface states also leads to efficient spincharge conversion at room temperature [6,7], allowing one to envision novel devices for universal memory and spin-based logic.
[1] M. Neupane, A. Richardella et al., Nature Communications 5, 3841 (2014).
[2] A. Kandala, A. Richardella, et al., Nature Communications 6, 7434 (2015).
[3] E. Lachman et al., Science Advances 1, e1500740 (2015).
[4] M. Liu et al., Science Advances 2, e1600167 (2016).
[5] A. L. Yeats et al. PNAS (online 12 September, 2017).
[6] A. Mellnik, J. S. Lee, A. Richardella et al., Nature 511, 449 (2014).
[7] H. Wang et al., Physical Review Letters 117, 076601 (2016).

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