Sunday, 14 May, 2017, 4:00-6:00 pm

Topological Spintronics

 

Prof. Nitin Samarth
Department of Physics
The Pennsylvania State University
University Park PA 16802 USA
nsamarth@psu.edu

 

Narrow band gap semiconductors such as the Bi- and Sb-chalcogenides are now known to support topologically protected, two dimensional (2D) helical Dirac fermion surface states characterized by a spin-texture in momentum space [1]. Originally predicted by first principles calculations [2], spin- and angle-resolved photoemission spectroscopy firmly demonstrated [3,4] the linear dispersion and the “spin-momentum locking” of the 2D surface states in these three dimensional (3D) “topological insulators.” More recently, the spin-momentum locking has also been measured using electrical transport measurements [5-8], albeit in devices where the chemical potential is not unambiguously in the bulk gap. The spin-momentum locking of 2D helical Dirac states lends itself naturally to spintronic device applications and is in particular expected to result in efficient spin-to-charge conversion. This tutorial will present an overview of concepts and experiments that explore the emergence of “topological spintronics,” a potential device technology that exploits the strong spin-orbit coupling in topological insulators for manipulating the magnetization of a vicinal ferromagnet [9,10].

We first discuss experiments that use spin- and angle-resolved photoemission spectroscopy to show how the helical Dirac spin texture of 3D topological insulators can be engineered using quantum tunneling between surfaces [4]. We then discuss electrically-gated spin transport devices that enable electrical measurements of the spin-momentum “locking” in surface states as a function of the chemical potential [10]. Finally, we discuss a variety of methodologies that allow one to both probe spin-charge conversion and spin transfer torque at room temperature in heterostructure devices that interface a 3D topological insulator with metallic or insulating ferromagnets [9,12-14].

 

I. REFERENCES
1. M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82, 3045(2010).
2. Haijun Zhang et al. Nature Physics 5, 438 (2009). 3. D. Hsieh et al., Nature 460, 1101 (2009).
4. M. Neupane, et al., Nat. Commun. 5, 3841 (2014).
5. C. H. Li et al., Nature Nanotechnology 9, 218 (2014).
6. Y. Ando et al., Nano Lett. 14, 6226 (2014).
7. A. Dankert, J. Geurs, M. V. Kamalakar, and S. P. Dash, Nano Lett. 15, 7976 (2015).
8. J. Tian, I. Miotkowski, S. Hong, and Y. P. Chen, Scientific Reports 5, 14293 (2015).
9. A. R. Mellnik et al., Nature 511, 449 (2014).
10. M. E. Flatte, AIP Advances 7, 055293 (2017).
11. J. S. Lee et al., Phys. Rev. B 92, 155312 (2015).
12. M. Jamali et al., Nano Lett. 15, (2015).
13. Hailong Wang et al., Phys. Rev. Lett. 117, 076601 (2016).
14. Y. Lv et al., arxiv:1701.06505